IoT & Hardware Hacking for Beginners – Learn Fundamenta… — Transcript

Welcome to the beginner's guide to IoT and hardware hacking on YouTube. If you are interested in learning about IoT and hardware hacking, then you are absolutely in the right place. We're going to get over to the course very shortly. But before we do, just a quick few items of note. First one is my name is Andrew Bolini. I also go as Digital Andrew and I am the creator of this course. I also have my own YouTube channel, Digital Andrew, that I will drop a link to down below where I'm going to be posting a lot of IoT and hardware hacking content and lessons in 2026. So check it out and if you are interested, make sure you are subscribed. The second thing is this is the YouTube version of the course which is in its entirety on TCM Security Academy. This YouTube version is going to cover the first approximately two-thirds of the course. So if you want to get access to the entire course and those last few sections, then go ahead and check out the TCM Security Academy. I will drop a link to it down below. You'll also get things like a certificate of completion when you complete the course as well. And then finally, we also have a certificate that goes along with this course called the Practical IoT Pentest Associate or PIPA for short. And if you are interested in challenging that or challenging yourself to take that, I will drop a link to all of the details about that down below. So, with that being said, let's actually hop over to the course now. I hope you enjoy it. Welcome everyone to the beginner's guide to IoT and hardware hacking. First off, thank you so much for choosing to take this course. I've got some really exciting material and I cannot wait to get started on it. Before we do, in this video, we're going to cover some of the standard course intro topics such as a brief introduction about myself, a little bit on the course curriculum, and then some of the course prerequisites. So, without further ado, let's get started with the intro. So to start just a little bit about me. My name is Andrew Bellini and my background is in electrical engineering. I have a bachelor's of engineering science focusing on electrical engineering and then more specifically specializing in wireless technology. I'm also a licensed professional engineer in Ontario, Canada. Throughout my career, I've worked as an electrical engineer working across many different industries including SCADA control systems and also embedded systems and electronics for the rail industry. I'm also a TCM student and I actually took the PH course many years ago when it was only available through Udemy and I actually now work as a cybersecurity technical trainer for a cybersecurity company where I train the employees. I generally go by Digital Andrew on my social media and that's how you'll see me in Discord. And the best way to get in touch with me if you want to reach out is through my LinkedIn which I've linked here. You can also reach me on Twitter and then I also have a website. Just a few quick non-technical details about me in case you're interested. I am a dad. I love to play guitar. I play in a band. So if you're any good at Osent, you can probably track me down there. And I also love the outdoors and fishing. Okay, so moving on. Let's take a look at the curriculum for the course. So we're going to begin with Electrical Engineering for Hackers 101. And this is going to be a mostly theoretical section of the course where we will learn about some of the most important fundamentals of electricity, electrical engineering, and electronics. In the second section of the course, we're going to take a hands-on look at PCBs, some of their characteristics and components, and then learn how to use multimeters. We'll then move on to the third section of the course which is a continuation of Electrical Engineering for Hackers where we will continue to learn about some of those fundamental theories of electricity, electrical engineering, and electronics. After that, we'll move on to a hands-on section where we learn about logic analyzers and how we can use those to measure and sniff out UART communication and in doing so learn about UART. We'll then move on to some hardware recon and OSINT where we'll take a look at the various recon we can perform on our hardware and then the additional information that we can find open source on the internet. After that we will hook up to the router with the UART shell that we found and we will actually do some live enumeration of our router. In the next section of the course, we're going to learn about SPI or Serial Peripheral Interface protocol and then we will actually use that protocol to extract the firmware off of the router and then we'll perform some analysis on that firmware. In section 8, we will then actually do some reverse engineering of that firmware and take a look at how we can start to look for vulnerabilities in it. We'll then do a quick course challenge and course wrap-up. Before we move on to the prerequisites of the course, I do just really want to quickly chat about why I've included some theory sections about electrical engineering and electronics in this course. So, one of the questions that I very frequently see asked about ethical hacking is, do I need to understand programming or learn how to program? And you know the answer to that or the one that I kind of think is the best answer is that you know you definitely don't need to fully understand programming or be a programmer to get into ethical hacking. However, you know the more you understand about programming, some of the fundamentals of it and actually, you know, being able to look at code and understand how that code functions, this is of course going to make you a much better ethical hacker and help a lot. So, of course, you know, if you're doing web penetration testing, then you don't need to know how to go and build out a website, you know, from the ground up and understand fully how to do that. However, you should be able to look at the code and have a good understanding of what it's doing. And this is the same for hardware hacking, or at least that's my belief. You don't need to be, you know, a full-fledged electrical engineer, fully understand electronics, or be able to design a circuit from the ground up. However, it's going to benefit you a lot if when you take a look at circuits, you get an idea of, you know, what is going on with that circuit and you're able to identify the different components. And that's why I have included the two theoretical sections on Electrical Engineering for Hackers. So if you are finding that these are too much, you know, like school, you just want to get to the hacking, then of course this course is yours to make what you want with it and you know, I would encourage you to then just move on to some of the hacking sections. But I do think that they will be really beneficial to you if you do want to in the future continue on with hardware hacking. With that being said, let's move on to the course prerequisites. So there aren't actually a lot of prerequisites for this actual course. I have listed it as a beginner's course and I do just want to quickly chat about that. What I mean by beginner is that this is a beginner's course to hardware and IoT hacking. Hardware and IoT hacking in itself is somewhat of a complex topic in that it covers a broad range of different underlying topics. So, you know, I would consider this to probably be like an intermediate level course if you're just looking at it, you know, from an outward lens. And then it's more of a beginner's hardware and IoT hacking course. So with that being said, I think it's going to be really beneficial for you if you have a general understanding of Linux because a lot of the IoT devices that we're going to be looking at and specifically the router that we're going to be working on this course are going to be running embedded Linux and then of course we're going to be...

shortly. But before we do, just a quick few items of note. First one is my name is Andrew Bolini. I also go as Digital Andrew and I am the creator of this course. I also have my own YouTube

channel, Digital Andrew, that I will drop a link to down below where I'm going to be posting a lot of IoT and hardware hacking content and lessons on in 2026. So check it out and if you are interested, make sure you are

subscribed. The second thing is this is the YouTube version of the course which is in its entirety on TCM Security Academy. This YouTube version is going to cover the first approximately twothirds of the course. So if you want

to get access to the entire course and those last few sections, then go ahead and check out the TCM Security Academy, I will drop a link to it down below.

You'll also get things like a certificate of completion when you complete the course as well. And then finally, we also have a certificate that goes along with this course called the practical IoT pentest associate or PIPA for short. And if you are interested in

challenging that or challenging yourself to take that, I will drop a link to all of the details about that down below.

So, with that being said, let's actually hop over to the course now. I hope you enjoy it.

Welcome everyone to the beginners's guide to IoT and hardware hacking. First off, thank you so much for choosing to take this course. I've got some really exciting material and I cannot wait to get started on it. Before we do, in this

video, we're going to cover some of the standard course intro topics such as a brief introduction about myself, a little bit on the course curriculum, and then some of the course prerequisites.

So, without further ado, let's get started with the intro. So to start just a little bit about me. My name is Andrew Bellini and my background is in electrical engineering. I have a bachelor's of engineering science focusing on electrical engineering and

then more specifically specializing in wireless technology. I'm also a licensed professional engineer in Ontario, Canada. Throughout my career, I've worked as an electrical engineer working across many different industries including SCADA control systems and also embedded systems and electronics for the

rail industry. I'm also a TCM student and I actually took the PH course many years ago when it was only available through Udemy and I actually now work as a cyber security technical trainer for a cyber security company where I train uh

the employees. I generally go by digital Andrew on my social media and that's how you'll see me in Discord. And the best way to get in touch with me if you want to reach out is through my LinkedIn

which I've linked here. You can also reach me on Twitter and then I also have a website. Just a few quick non-technical details about me in case you're interested. I am a dad. Uh I love to play guitar. I play in a band. So if

you're any good at Osent, you can probably uh track me down there. And I also love the outdoors and fishing.

Okay, so moving on. Let's take a look at the curriculum for the course. So we're going to begin with electrical engineering for hackers 101. And this is going to be a mostly theoretical section of the course where we will learn about

some of the most important fundamentals of electricity, electrical engineering, and electronics. In the second section of the course, we're going to take a hands-on look at PCBs, some of their characteristics and components, and then learn how to use multimeters. We'll then

move on to the third section of the course which is a continuation of electrical engineering for hackers where we will continue to learn about some of those fundamental theories of electricity, electrical engineering and electronics.

After that, we'll move on to a hands-on section where we learn about logic analyzers and how we can use those to measure and sniff out UART communication and in doing so learn about UART. We'll then move on to some hardware recon and

OSENT where we'll take a look at the various recon we can perform on our hardware and then the additional information that we can find open source on the internet.

After that we will hook up to the router with the UART shell that we found and we will actually do some live enumeration of our router.

In the next section of the course, we're going to learn about SPI or serial peripheral interface protocol and then we will actually use that protocol to extract the firmware off of the router and then we'll perform some analysis on

that firmware. In section 8, we will then actually do some reverse engineering of that firmware and take a look at how we can start to look for vulnerabilities in it.

We'll then do a quick course challenge and course wrap-up. Before we move on to the prerequisites of the course, I do just really want to quickly chat about why I've included some theory sections about electrical engineering and electronics in this course. So, one of

the questions that I very frequently see asked about ethical hacking is, do I need to understand programming or learn how to program? And you know the answer to that or the one that I kind of think is the best answer is that you know you

definitely don't need to fully understand programming or be a programmer to get into ethical hacking.

However, you know the more you understand about programming uh some of the fundamentals of it and actually you know being able to look at code and understand how that code functions this is of course going to make you a much

better ethical hacker and help a lot. So, of course, you know, if you're doing web penetration testing, then you don't need to know how to go and build out a uh website, you know, from the ground up and understand fully how to do that.

However, you should be able to uh look at the code and have a good understanding of what it's doing. And this is the same for hardware hacking, or at least that's my belief. You don't need to be, you know, a full-fledged

electrical engineer, fully understand electronics, or be able to design a circuit from the ground up. However, it's going to benefit you a lot if when you take a look at circuits, you get an idea of, you know, what is going on with

that circuit and you're able to identify the different components. And that's why I have included the two theoretical sections on electrical engineering for hackers. So if you are finding that these are too much, you know, like school, you just want to get to the

hacking, then of course this course is yours to make what you want with it and you know, I would encourage you to then just move on to some of the hacking sections. But I do think that they will

be really beneficial to you if you do want to in the future continue on with hardware hacking. With that being said, let's move on to the course prerequisites. So there aren't actually a lot of prerequisites for this actual

course. I have listed it as a beginners's course and I do just want to quickly chat about that. What I mean by beginners is that this is a beginners's course to hardware and IoT hacking.

Hardware and IoT hacking in itself is somewhat of a complex topic in that it covers a broad range of different underlying topics. So, you know, I would consider this to probably be like an intermediate level course if you're just

looking at it, you know, from an outward lens. and then it's more of a beginners's hardware and IoT hacking course. So with that being said, I think it's going to be really beneficial for you if you have a general understanding

of Linux because a lot of the IoT devices that we're going to be looking at and specifically the router that we're going to be working on this course are going to be running embedded Linux and then of course we're going to be

using uh Kali Linux as well as our attack machine. And then also you should have a basic understanding of penetration testing and some of those principles. So if you're not feeling brushed up on these topics enough then I

would suggest there's a very good uh Linux course in the TCM Academy that would go over everything that you would need to know. And then of course the practical ethical hacking course um by TCM Academy is also an excellent

precursor to this if you're not feeling brushed up on penetration testing. So then just the things that you do not need to know though is if you don't have any background uh in electrical engineering or knowledge of electricity

or electronics that's okay we'll cover all of that. You do not need to know how to use any of the tools that we're going to be using. So either software or physical. So things like the multimeter or the logic analyzer. We'll go over all

that. And then you do not need any specific knowledge on IoT devices. We will cover all of that. So that wraps up this video. I do have a couple of quick videos after this that go over some really important uh notices or topics.

So, I would really encourage you please watch those before moving on to the course. But that wraps up this video.

I'll see you over in the next one. Welcome everyone. So, this video I've just got a really quick notice to make about the TPLink router that we're going to be using uh in this course. So, if you're anything like me, you may have

gone ahead and bought these and you just want to open it up and check everything out. Uh, and that's all good to do, but I just want to quickly show you um one thing that I think most people will

throw away and we're going to try and keep uh in this course. So, this is not just your standard unboxing video. I just want to really quickly show you something. So, just going to open up the uh box here, actually.

And then, so inside of the box, there is. Let me just grab it. Should come with a power supply I've got here. And it's just in this baggie. So, I'll pull it out of the baggie.

Uh, and then you'll notice that the actual cable of the power supply, it's secured with this twist tie here. If I just hold up in front of the camera. Uh, yeah. So, this twist tie when you take this off. So, I'll just take it off

quickly right now. Just go ahead and, uh, hang hang on to this here. We're going to be using this later on in the course for kind of like a little bit of a hacky way to attach um, some of our

equipment if you don't want to do soldering. So, I suggest you hang on to this. I mean, if you throw it out, you can probably find these. They're easy to find, but just wanted to keep give you a

heads up. hang on to this. So that's all for this video. I'll see you over in the next one. Welcome everyone. In this video, we're just going to do a quick reminder about ethical hacking. So if you are familiar with ethical hacking

and this isn't your first fora or course, then this is something you're probably familiar with and this will just be a quick reminder for you. Uh and if you're not familiar with this, then definitely pay attention.

So, the first thing that I just want to go over or cover is that of course you should be following all of your local laws and regulations. And that, you know, nothing in this course is meant to violate any laws or regulations. Of

course, they do vary from region to region. So, make sure you're aware of your regional laws and regulations. And if you're in doubt about any of it, then those should take precedence over anything in this course. The second

point, this is a really important one, is that we should only be testing, practicing, and hacking on your own uh device. So, in this course, we're going to actually be focusing on IoT devices, and we're actually going to be working

on real physical IoT devices. We're going to be working on a router. And you should only target your own equipment or equipment that you have permission to test. And this is a really important one because with IoT devices, they are so

ubiquitous now. Um they're all over the place. A lot of times they can have uh weak security and you know gaps or things like that in them and it can be really tempting to even just poke around um on other people's IoT devices, either

your neighbors or things like that. And you know, you may think that you can easily get away with it, but the consequences for it are very real and they're very big. So it's not worth it.

only test and only work on and only practice on either your own device or one that you have specific permission to be testing on. So the next point I want to talk about is practicing responsible disclosure. So this course actually uses

a real world device for educational purposes. And because of that I'm not actually going to be showing any specific vulnerabilities on it. will just be using it for testing uh and showing techniques. But we're not going to be showing any vulnerabilities

because of course feel like if I were to show um any of those on this then they would need to then be reported and then patched and the firmware would be out of date already then by the time the course

starts. However, you know, if you are to uncover um any potential vulnerabilities either on the device that we're working on in this course or when you move on, you know, in your IoT and hardware hacking experiences and you work on

other devices, then I really encourage you to um practice responsible disclosure if you do come across any of those vulnerabilities. And if you're not sure how to do that, then just, you know, do a quick Google search. There's

lots of really good videos about how to properly do responsible disclosure. And then just as a final reminder and a catchall, you know, we should be responsible, ethical, and moral in all of our actions. And I think, you know,

those are just three really good things to follow. And, you know, if we follow those, then that's going to cover, you know, most of what we should be doing.

So, again, just a really quick reminder of how important these topics are and how important they are that you actually follow them throughout this course and in what you do. Thank you for watching this. That wraps up this video.

Welcome everyone to the first section of this course, electrical engineering for hackers 101. In this section of the course, we'll be taking a look at some of the key fundamental concepts of both electricity and electrical engineering.

We're starting out with these theorybased lessons to gain foundational knowledge that will be required to understand the topics and techniques we'll be covering in future lessons on hardware hacking. I've worked my best to condense these lessons into only the

most important and relevant topics that I learned during my electrical engineering degree along with the knowledge I needed on a day-to-day basis as an electrical engineer working with electronics.

The lessons in this section and the following 2011 section will get more practical as we progress and we'll have hands-on portions. Before you know it, we'll be directly applying the theory learned in actual hardware hacks. I'm excited to get started and we'll see you

over in the first lesson. Welcome everyone. Throughout this lesson, we're going to be working to answer the fundamental question, what is electricity? And what are the units that we use to measure and describe it?

In order to get started, we need to shrink things down all the way to the atomic level. And we're going to start our example by looking at a carbon atom.

At the center of the atom is the nucleus. And the nucleus is made up of two particles, protons and neutrons.

Protons are positively charged particles and neutrons are neutral. The protons and neutrons make up most of the mass of the atom and therefore stay close to the center in the nucleus. The amount of protons an atom has is a fixed number

and this number is actually what determines which element it is. For carbon, which has the elemental number of six, this means that it has six protons. Generally there will be the same amount of neutrons as protons.

However, this can differ. The third particle of the atom is the electron. Electrons have a negative charge and they are much much lighter than protons and neutrons. As such, they exist around the nucleus. And one way that we can describe how they move

around the nucleus is what we call orbits or shells. The negative charge on the electron is attracted to the positive charge of the proton and this is what keeps it in these shells.

This two-dimensional model of the atom with the electrons orbiting in shells is referred to as the Bore Rutherford diagram. I've put an asterisk here because I do want to note that this is not actually an entirely accurate model.

However, it is good enough for the understanding we need. So, these electrons, as we know, exist in these shells that orbit the nucleus. And each shell can hold a specific set amount of electrons. In the first shell, this is

two and in the second shell, this is eight. Unlike protons that are fixed to the atom, in some circumstances, electrons are able to move from atom to atom, either leaving an atom and joining another or in the opposite, an atom will

pull an electron from another atom. When this happens, the atom becomes what is called an ion. And an ion is a negatively or positively charged atoms.

It either has a surplus or deficit of electrons. In this example, we have what's called a cat ion because we have more electrons than protons and this gives the atom a negative charge.

The opposite of this is an annion. In this example, we have more protons than electrons and this gives the atom a positive charge.

This ability of electrons to flow from one atom to another and to also create positively and negatively charged atoms is the fundamental for electricity and how we are able to harness it. Let's take a look at how we can harness the

flow of these electrons for electricity. We'll start by looking at arguably one of the most common conductors and that is copper. You'll notice that copper only has one electron in its outer shell. This outer shell is called the

veence shell and the electrons in it are called the veence electrons. Copper's single veence electron is very loosely bonded to its nucleus and this makes it easy to travel from atom to atom. This makes it what we call an

excellent conductor. Atoms with this looser hold on their veence electrons allow them to move freely from one conducting atom to another.

If we add a second copper atom closely, we can see that the veence electron can easily move from one copper atom to the other. In fact, in a piece of copper that may have millions to billions of these copper atoms in them, this veence

electron just flows freely between all of the atoms. At this point, this does not constitute electricity though because we just have this random movement. In order to turn this into electricity, we need to be able to control the flow.

Let's now take a look at how we can harness this movement of electrons. If we take a look at the cross-section of a copper wire, which could be made up of millions to billions of atoms, we know that each of these atoms has veence

electrons that can fle freely flow from one to the next. If we are able to control this flow and have it move through the wire in a specific direction, then we can have a flow of electricity or an electrical

current. And this electrical current is a stream of charged particles, generally electrons, moving through a conductor.

And we measure this in amps. Now, you'll notice that I have the arrow for the electric current pointing in the opposite direction of the flow of electrons. This is not a mistake, and we'll chat more on this later. Of

course, at rest, we will not have this electrical current or flow of electrons in any meaningful direction. The movement of the electrons will be random. Let's now take a look at how we can control this flow of electrons.

In order to move the electrons, we need a force to push them. One great example is a battery. A battery creates a chemical imbalance in electric charges.

The fundamental rule of nature that opposites attract will cause the negatively charged surplus electrons to want to flow to the positive side of the battery. If we connect a conductor such as a copper wire between these that will

facilitate this, this negative charge will push the electrons through the wire. This imbalance of charges is what we call electrical potential difference.

And this is the difference in electrical potential between points and we refer to this as voltage. Commonly this is a buildup of charge and we measure this in volts. Now that we understand how we can control this flow of electrons, how can

we harness it for power? The movement of an electric charge causes energy to be transferred. If, for example, we just connected this battery with a copper wire, then most, if not all of this energy will just turn into

heat. This is actually a bad example in real life, and you'll most likely just cause a fire. This is what's called a short circuit. However, if we put an electrical component in the way like a light bulb, then this electrical charge

will be transferred into other useful forms of energy. In our example, light. We can describe this flow of charge through the circuit's ability to transfer into other meaningful forms of energy as electric power. The electric power is proportional to both the flow

of electrons and the charge imbalance that is pushing them through. As such the electric power is proportional to the voltage and current. So to calculate power we just multiply the voltage by the current. Now power is not to be

confused with energy which is a measurement of the amount of power delivered over time.

You remember previously I was chatting about how I had the arrow drawn backwards and that is because the conventional flow of electricity or how we refer to it is actually opposite to the flow of electrons. The convention for the flow of electricity is from

positive to negative charges. This may be a little confusing at the start and the reasoning for this is actually because when electricity was first being discovered it was thought that electrons flowed from the positive to negative charge and as such the convention of

drawing circuits with the electrical flow flowing from the positive charge to the negative charge was set as this direction. Later on it was discovered that electrons flowed in the opposite direction. However, this original convention was kept. In reality, it

doesn't actually matter that much as long as everyone agrees to use the same notation.

Of course, way back when we were discovering the atom, we could have just decided that protons would be a negative charge and the electrons would be a positive charge. It is all really relative. The last fundamental concept that we'll discuss now is that of

electrical resistance. So we know that the voltage pushes the electrons through a conductor which causes an electric current. But how much electric current does this voltage create? Of course, we do know that as we increase the voltage, the electrical current increases. The

amount of current that flows for a specific voltage is proportional to the resistance of the material that it is flowing through. In copper, we have an excellent conductor and there is very little resistance. Our light bulb though for example has much much more

resistance than copper and as such resists the flow of electricity. This resistance of the flow of electricity is what causes most of the voltage to be transferred over the light bulb and as such most of the power is transferred

into the light bulb as opposed to just being lost as heat in the wire. We call this electrical resistance. And the electrical resistance is the measure of an object's opposition to the flow of electric current. It's the opposite of

conductivity and we measure this in ohms. That wraps up this part of the lesson on our discussion about what electricity is, its fundamental properties, and the units that we use to describe it. We'll pick up in the next lesson talking about

what electricity is, and using a popular analogy comparing electrical flow to water. I'll see you in the next lesson.

Welcome everyone. In this first of three videos on electrical engineering fundamentals, we're going to take a look at how we can represent circuits with schematics. What resistors and voltage sources look like in these schematics and in real life. And then we'll wrap up

with the very first fundamental law of electrical engineering, ohms law. As a very quick recap from our last lesson, some of the key points that we learned about were voltage, which is caused by an imbalance of charge and

creates a pushing force for electrons through a circuit. This flow of electrons through the circuit is what we call electrical current. And as this electrical current passes over a resistance, it causes a voltage drop, which is turned into power. The power

can be calculated as the current multiplied by the voltage. This pictographic representation of the circuit that we have is not a very efficient one. So let's take a look at how circuits are commonly drawn.

Throughout the rest of this lesson, we're going to be drawing our circuits as schematics. Schematics are a visual representation of circuits. A few things to keep in mind about schematics. The wires in schematics are represented by the black lines.

These wires are what we call ideal conductors. This means that there is no resistance in them and therefore the length of these wires does not matter.

In fact, schematics are not to scale at all and they do not actually represent how the circuit is physically laid out.

We use many other symbols in schematics to represent different electrical components and throughout this lesson we're going to be looking at a couple of them. Let's start with how we are representing our voltage. You'll see here how we have V1 representing the

voltage drawn as a symbol with a circle and then a positive and a negative representing the polarity of each side.

A real life example of this would be a power adapter that plugs into the wall.

Here I have pictured the one that comes with our TPLink router. If you look at it closely, you'll notice that there is an output label and the output is for 9 volts. And then we have this symbol here

which represents direct current, something that we're going to talk about later. And then we have an amperage rating of 0.6 amps. What this output rating tells us is that this adapter operates at 9 volt. So its output is 9

volt. And then the current we see is not actually the current that's always supplied. This is just a maximum rating.

So the maximum current that can be supplied. Now that we know the voltage is 9 vol, let's work at trying to actually figure out the current. The first thing that we need to take a look at in order to do so

is actually the resistance. A resistor is represented in a schematic by the squiggly line that's drawn here.

In real life on a circuit, they may look something similar to the picture here.

However, they come in multiple packages. Resistors are one of the most common electrical components in circuits as they are essential to how we control the flow of electricity and can divide voltages.

For our example here, let's say that our resistor has a resistance of 100 ohms.

In order to calculate the current, we'll look at the first fundamental electrical engineering law that we're going to introduce in this lesson, which is Ohm's law. Now, Ohm's law states that the voltage is equal to the current time the

resistance. In this case though, we would like to calculate the current. Using a little bit of simple algebra, we can rework the formula so that it is I= V / R or current is equal to the voltage / the

resistance. If we plug in our numbers from the circuit, then we get that the current is equal to 9 V / 100 ohms.

Plugging this into our calculator, we'll get that the current is equal to 0.09 amps or another very common way to write this is as 90 milliamps. Resistors will commonly have a power rating that specifies how much power can safely be

dissipated across the resistor. If we surpass this power rating, then the resistor may catch fire. Let's look at how we can calculate the power that is dissipated across this resistor.

You'll recall that the power is equal to the current * the voltage. So in our case, this is equal to 90 milliamps * 9 vol, which is equal to 0.81 W.

Welcome everyone. In this second video of electrical engineering fundamentals, we're going to take a look at the second fundamental electrical engineering law, Kaw's voltage law. And then we'll take a look at series circuits. Before we move on to looking at the second fundamental

electrical engineering law, a quick reminder on conservation of energy. So because of conservation of energy, this means that we can't actually lose any electrons. So what that means is that the current is equal throughout an entire closed loop. In our circuit here,

I've drawn the flow of the current with red. And you'll notice that throughout the whole closed loop, this current is equal throughout the whole thing. the electrons have nowhere to go as they must remain in the conductor and as such

the flow is equal from one point to another throughout the entire circuit. With this in mind, let's take a look at our second fundamental law of electrical engineering. And that law is Kirchaw's voltage law. Now, Kirchaw's voltage law

says that the sum of all voltages across a closed loop circuit is equal to zero.

And in order to better demonstrate that, I'd like to talk about another schematic element. And that is the idea of circuit nodes. So a circuit node is a point or region on a circuit between two circuit elements. And I'll put one up here on

our schematic. So on our schematic, we actually have two nodes. The first one being right here as we have a joining connection between the positive end of our voltage supply and our resistor. and then the second one being the joining end of the

negative side of our voltage supply and the resistor. So what Kirchaw's voltage law means for this sum of all voltages across the closed loop circuit is zero is that if we go around this circuit, so you'll notice how I've drawn it here,

all of the voltages across this have to equal zero. So if we were to measure the voltage across this 100 ohm resistor, we know of course that it's going to equal 9 vol. Now you may be wondering how does

9 vol 9 vol equals 0. Well in this case using the convention of a current flowing from positive to negative when we have a current that flows through a voltage source. So from this positive to negative that means that this voltage is

an additive voltage. So we are adding 9 vol. Since the resistor is not actually supplying power rather consuming it, you'll notice that we have the polarity swapped. So this is from positive to negative. As the current flows from a

positive to negative, we actually have a voltage drop. So one way to write this would actually be as - 9 volt. Now commonly in circuits you won't actually see these voltages as positive and negative and instead you will see the

voltage source generally labeled as negative to positive and then elements that consume power it's just inferred that it's going to be this positive to negative. So one way that we could actually write this or look at it as

this is as + 9 vol and then this is as - 9 volt and it equals to zero which satisfies Kaw's voltage law. The next concept we'll chat about is that of a series circuit. So in a series circuit

components are connected end to end one after another in such a way that they create a single path for current to flow. So you'll notice in our circuit here that we have added an additional resistor but our resistance still is

equal to 100 ohms and this is because resistances in series can be added together and as such our current is still equal. However, our voltage will be divided amongst these two. Using Ohm's law, we can calculate that the

first voltage will be equal to 2.7 volt. And then we could either use Kirchaw's voltage law or Ohm's law to calculate that the next voltage will be 6.3 volt.

Of course, our 2.7 volts in 6.3 volt adds up to our 9 volt to satisfy Kaw's voltage law.

What happens in our series circuit if we add two voltage sources in series with each other? If we look at Kraw's voltage law, of course, we know that this is going to be 18 volts.

As our current travels through the circuit in our loop again, when it goes from this minus to positive and this minus to positive, we're going to add 9 volts twice. So, we get 18 volts again.

Of course, since we've doubled our voltage and our resistance has remained constant, then we know due to Ohm's law that our current will also have doubled.

Hello everyone and welcome to the third and final video on electrical engineering fundamentals. In this video, we're going to take a look at parallel circuits and Kov's current law.

We'll begin the lesson by looking at parallel circuits. Parallel circuits are opposite to a series circuit in that components are connected to each other in such a way that current has more than one path to flow. If we look at our

example circuit here, we can see that we have added an additional 100 ohm resistor in parallel. The current that leaves from our voltage source once it reaches the node here will be able to be split between the two resistors with one

path flowing through this loop and the other path flowing through the outer loop. Kchaw's voltage law still applies to both of these loops and as such the voltage drop across the outer resistor will still be 9 volt. If we take a look

at the inner resistor, we'll see that the voltage drop is the same as well.

For series circuits, you may recall that the current remained the same through both resistors in series while the voltage was split in proportion to the resistance. For parallel circuits, it is the opposite. The voltage remains constant across both circuits in

parallel. However, the current is split in proportion to the resistance. In our example, the resistances are the same.

So, the current will be split evenly. As our initial current leaving our voltage source splits at this node, this means that we now actually have three currents. I1, which is the one leaving our voltage source. I2, which is the

current that travels across the first resistor, and then I3, which is the second current that travels across the outer resistor. The split of these currents brings us to our third and final of the fundamental electrical engineering laws which is Kirchov's

current law. And Kirchov's current law states that the sum of all currents entering and exiting a node must equal to zero. So in our case that means that I1 is equal to I2 + 3. Since I1 is entering this node and I2 and I3 are

leaving, we can determine that I1 will have a positive and I2 and I3 will both be negative. Instead of adding resistors in parallel, what happens if we add two voltage sources in parallel? You'll see that we now have I1 and I2 entering the

node and I3 exiting it. This means that I1 + I2 equal I3. Of course, using both Ohm's law and Kirchaw's voltage law, we can calculate that I3 equals 90 milliamps. As the voltage sources pushing I1 and I2 are both identical,

and we have no components for voltage drops between the nodes, we know that I1 and I2 must be identical. This allows us to calculate I1 and I2 as 45 milliamps.

If you didn't follow all the math on this one, that's all right. I just wanted to show here how adding two voltage sources in parallel does not actually increase the voltage. However, it splits the current demand on each

voltage source. This is important to remember especially when using batteries as we can add multiple batteries in parallel and this will extend the life of the battery as each one of them has a lower current draw. Now that we have an

understanding of Ohm's law, Kirchaw's voltage law, and Kirchaw's current law, let's take a look at how we can use all three of them in combination to solve out the currents inside of this example circuit. This is a fairly common

practice when designing circuits as we can choose both voltage sources and resistors from the market or offtheshelf that fit our needs. However, depending on the voltage sources and resistance we choose and how we configure them in the circuit, of course, this will change the

amount of current. The first step to take when solving our circuit is to label all of our currents in the direction they're flowing in. Of course, we have our main current I1 that is leaving our voltage source. And this

current is split into three separate currents across our parallel resistors. We have I2 traveling over the 100 ohm resistor. I3 traveling over the 30 ohm resistor. And then I4 that is traveling over a 30 ohm and 10 ohm resistor in

series. The next step we'll take in solving the circuit is to label out our voltage nodes.

What these voltage nodes represent is the voltage difference between the top node and the bottom node.

With our currents and voltage nodes labeled, we can start to write out the formulas that will allow us to solve for the currents in the circuit.

First, we'll use Kirchov's current law to define that I1 is equal to I2 + I3 + I4. As we know that the current entering the first node must be split into three separate currents and that they will all

equal the current entering the node. Using Ohm's law, we can calculate that each of the currents I2, I3, and I4 will be equal to the voltage drop over the resistor divided by the resistors. With that in mind, we can add those into our

first equation. We've substituted I2 for V1 / 100 ohms, I3 for V2 / 30 ohms, and then I4 for V3 / 40 ohms. Notice how we have combined the 30 ohm and 10 ohm resistor in series to equal 40 ohms. Next, we can use

Kirchaw's voltage law to solve for our voltage nodes. If we draw our first loop throughout this current, then we can determine that the voltage across this resistor is equal to 9 volt. Another way to look at this is that if we actually

just cross out this 9 volts and we look at this minus end as being zero and then this top end as being 9 volts. This 9 volts actually represents the difference between the two. We then can also write that our

node up here is 9 volts. And since we know that this node is connected to the negative end zero volts as the current travels in a circle through. So when we travel here from positive to negative we go from 0 to 9.

So plus 9 volt and then as we travel from this node down to here we go from 9 to 0. So we go through - 9 volt.

As such we can say that V1 - 9 volt equals 0. And of course if we were rearrange that we can get V1 equals 9 volts.

In our scenario here these top three nodes we can think of as identical. We know that the wire in between are actually ideal wires. So there's no voltage drop between V_sub_1 or V2. And as such each of these have to equal 9 V.

Again, if we think of the additional loops, this also satisfies Kirchaw's voltage law. Because of this, we can set V_sub_1 equal to V2 equal to V3.

With all the values for our unknown variables accounted for, solving for I1 is as easy as plugging the numbers into our calculator.

We can calculate I1 as equal to 9 vol / 100 ohms + 9 vol / 30 ohms + 9 vol / 40 ohms. If we plug these all in, we'll get that I2 = 90 milliamps, I3 = 300 milliamps, and I4 = 225

milliamps. If we add these all together, we'll get I1 equal to 615 milliamps, which is actually 0.615 amp.

For those of you keeping score from our initial look at the voltage source, if this were that same voltage source, then we have actually surpassed the amperage rating or the current rating. So, something to keep in mind when we're

calculating and designing our circuits. You may have noticed that even for this quite simple and basic circuit, the algebra and math starts to add up.

Fortunately for us, there are many great circuit simulation tools that can take care of all these calculations for us.

And this is rarely done by hand. However, it is really important to understand the fundamentals of these three basic laws and how they work in order for us to set these simulations up.

This wraps up our three-part series on electrical engineering fundamentals. I'll see you in the next lesson.

Hey everyone. So, we left off at the end of the last lesson chatting about how there's lots of great circuit simulators that can actually do most of these simulations for calculating currents and voltage nodes. And honestly, there's a

lot more that they can calculate. And in the past, these simulation softwares were pretty expensive, and realistically, you could only get access to them if you work for a company that was going to buy a license. But now,

there is a few good ones that you can get for free. And this Circuit Lab is one that I just wanted to show everyone quickly. It's pretty cool and it runs right in a browser. Um, so you can get

to it from circlab.com. And if you want to watch their intro video or get started, feel free to take a look at that. And then if you uh scroll down, there's some great examples and lessons and things like that.

However, I'm just going to jump right in and show you how we can do a quick simulation. And then maybe if you want to take over and play around, that would be awesome. So, at the time of recording

this, you don't even need a login or anything like that. You can just go right into Launch Circuit Lab, and it's going to open up their simulator right in the browser. And you can just copy everything here. I'm just going to drag

and drop, and we'll just delete it all. Uh, and I'm going to quickly lay out that last circuit that we were looking at in the previous lesson. So, we'll start by grabbing our voltage source that we had. And if we just double click

here, we can edit the voltage here. And we'll make it 9 volts. And I'm just going to make it I'm just going to call it VC source for the voltage source.

All right. And then we'll add in our resistors. So we had our 100 ohm resistor here. And then we had a 30 ohm resistor here.

And then we had a 30 ohm and a 10 ohm here. So you just double click on them. You can edit 30 and then 10.

So now we just need to add our wires in to close this up. You just grab a wire here and you just draw the wire by dragging and clicking, which is awesome.

You just drag and click. Let's bring these all together. And then the one thing you're always going to have to add for the circuit simulations is we still need a ground um because it all works off of reference

voltages. So we haven't really talked too much about grounds yet and we will um in upcoming videos, but we need to tie all of our returns to a ground. And this just lets the circuit simulation know that, you know, this negative

polarity here that all this is tied to um a zero reference voltage as opposed to um it being a floating voltage and it's going to need that in order to solve it. So if you run a simulation without this ground, it's going to fail.

So the last thing we can do is just add some node names so that it makes it a little bit easier for us to um know what voltages it's talking about when it's solving. So, I'm going to drop in some

node names. And we had called this one V1 before. And we'll add one here for V2.

And then we'll add a final one here for V3. You'll see if I hover them already, it's telling me what voltage it is. So, that is pretty cool. Um, just like we suspected. So, we have because of KVL,

we know that it's going to be 9 volts for all of these reference points. And you may have noticed that actually as soon as I added the ground to the circuit, it satisfied all the conditions for it to run the simulation and it

automatically actually populated all of the currents and powers and voltages. So, if we just hover over the nodes, we can actually see all of those details.

If we hover over here for example, of course the voltage is 9 volts and we can see that then we're 90 milliamps. And if we hover over here, um just to give an idea of that voltage drop that I was

talking about, we can actually see the 0 volts now as we have that full current drop, but the current remains the same.

Uh and then of course we can also see the power which is kind of cool. If we go through to the other nodes, of course we have 9 volts again and we can see that second current as 300 milliamps. uh

over here if we look at these resistors of course we have this 225 milliamps and then we can also see uh the voltage drop across each of these resistors.

Uh and then if we go down over here we can see the source at 650 milliamps.

This is just a really really basic example and honestly it just scratches the surface of what this software is capable of and it's pretty cool that we're able to get free access to it. So, I'd highly recommend checking it out,

hopping in here, creating a few circuits yourself, uh, playing around with it, running some simulations, and experimenting.

Hope you enjoyed this quick demo. I will see you over in the next lesson.

Welcome everyone to the first lesson on reading schematics. We will pick up again on this topic later on in the course. In this lesson, we're going to be taking a look at the difference between how a circuit may be represented

in a schematic versus actually physically laid out. We will also take a look at a couple of practical schematic drawings and how they differ from the theoretical schematics that we've been using so far. I've modified the schematic that we were previously using

to add a few new components. So you'll see here that we have replaced our 9volt power supply with the symbol which represents a battery and the longer line is the positive end and the shorter one is the negative. We've also added in two

LEDs or light emmitting diodes, a red one and a green one. And we've also added in a switch. This symbol here is a switch and when it's in this position it represents open and when it's like this it represents closed.

You may recall in one of the previous lectures that I mentioned how a schematic does not actually represent the physical layout of a circuit. And to demonstrate that, we're going to take a look at what is called a wiring diagram.

And a wiring diagram is a pictographic representation of how a circuit is actually physically laid out or wired up. So you'll see in our wiring diagram here of course we have our 9volt battery and we have this connector to it which

has a positive and negative leads. Um and our red wire actually represents the positive wire and you know usually wiring diagrams will give like wire lengths and wire colors so that someone can actually build the circuit. The first thing that I'd like to draw your

attention to is how we do have this split of parallel circuits that splits here. However, instead of here first going to the um red as our inner circle, we actually, you know, split up to our switch and go to the green. And that's

on the inside. And what I wanted to show by this is that the, you know, the ordering of the components or where they actually are in relation to each other on the schematic doesn't necessarily represent where they are physically laid

out. Of course, the electrical connections still matter and when, you know, we have them connected by this node. The second thing I'd like to point out is just the length of the wires. So you see here we have some long longer

wires. And this may be because if this is fitting uh you know this whole wiring wire up is fitting inside some mechanical case or something. We actually need these wires to be longer so they can route to where they need to

go on a schematic. Of course this does not matter. The other way that we can actually physically lay out circuits is on what's called a PCB or printed circuit board. and we'll be taking a deeper look at that in the hands-on

section once we open up the router. I've switched back our schematic to our voltage source that we are more familiar with because I want to show a couple of other different items that will happen when we are practically reading a

schematic. So the way that we have it drawn here, this is a valid way to draw a schematic. And when you're learning about circuits or electronics and especially electricity, you'll see the schematic drawn how it is here. Like if

you were looking in a textbook, this is a very common way to lay out a circuit when we're teaching. And the reason for that is because when we're talking about those loop currents that we were um with Kaw's voltage law and Kaw's currents

law, it's very easy to visualize the flow of the circuit. However, when we're actually drawing these schematics out on paper, it starts to take up too much room to show all these return loops and connect, you know, all these wires. So,

a very common way that you'll see schematics laid out is something like this, where we're representing our 9 volts with this line here. Um, and this isn't actually like a wire or anything.

It just represents that this is starting at 9 volts. And of course, this is the um exact same circuit here.

The other thing that I'd like to call out is this notion of ground, which is something that we have not talked about too much yet. And what ground means in these electronic style circuits like this is that this is all 0 volts. So,

this is just a reference at 0 volts. And we could add a ground here in this schematic and this would be totally valid stating that this is all zero volts. And the reason that you frequently won't see it in this style of

representation is as we were saying before generally this negative end of the voltage source represents 0 volts and ground also represents 0 volts. So by us having you know all of these tied together even without the ground it

represents that they are at 0 volts. The last thing on ground here is we can think of all of these grounds. So in a bigger circuit, you will start to see more and more grounds added on. They're all the same point. So it's the same as

if we took a wire and connected these together and then add one ground in order to reduce space and make the schematic a little bit less cluttered.

We just connect them all to their own ground as needed. You may also see a schematic like the one on the right laid out like this where we represent 9 volts with this pin style here or you might

see it like this. So all those are valid representations. The last thing that we'll take a look at in this first part of reading schematics is what happens when our schematics start to expand bigger and take up more

space. See that we start to have wires that need to run over each other. And there's a few ways that this is handled in schematics. The first one is where if we just consider anytime the wires touch like this that that actually represents

an electrical conductivity and as such we cannot cross wires like we did here. So we would use these kind of loop styles to demonstrate that this is not electrical connection and in fact this wire is going over. The other style

that's much more common in CAD style drawings is you will see anywhere there's actually an electrical connection or interconnection will have this circuit node style connection that you're used to drawing and then the wire will actually just go straight through

the other one. And this is this does not mean an electrical connection. Lastly, unfortunately there is not a set specific standard for all schematics. So you will see things differ between schematics. The one important thing when drawing them and also reading them to

keep in mind is that they should be uniform or standardized throughout the schematic. So this one is a bad example here where we're using um two different methods to show interconnection and jumping over wires.

Again, we'll pick up more on reading schematics in the next section, but this should give you enough information to get started on the course challenge.

I'll see you over there next. Hey everyone, we are nearing the end of the first section of the course and I just wanted to say great job on making it this far. We've covered topics that include math, science, and engineering

and I know that these are topics that you generally wouldn't find at the start of a hacking course. So, great job on persevering and making it through this section. If everything didn't click the first time on these videos, you had to

rewatch them a couple times, or even there's still some things that you're not fully understanding, that's okay.

These are topics and concepts that took me a while to figure out. And we did cover a lot of the topics and core fundamentals that would be covered in first year electrical engineering courses. And we did those pretty

quickly. If you're interested in these topics and you want to learn more, I'd highly encourage you to seek out some other resources on the internet, I really just scratched the surface of these topics because, well, of course, this is a

hacking course and I didn't want to take up all of our time with electrical engineering.

I've designed a fun course challenge that takes some of the theory that we've learned and applies it in a practical setting. So, let's dive right into the challenge briefing right now and take a look at that challenge.

Okay, welcome to the first challenge of the course. Red team needs your help. Let's take a quick look at the design briefing together.

It reads, "Ooperator, we require your immediate assistance. We're performing a covert red team operation tomorrow on a sensitive target. One of our field operatives discovered during initial recon that a back door at the site is locked using a smart lock and took some

pictures of the model. Luckily, we were able to procure some of the locks for testing in our lab. Our hardware team uncovered a transmission output on the board.

They were able to capture multiple transmissions and sent them over to our software team for analysis and decoding.

They discovered that at startup, the devices bootloader outputs to the transmit pin, followed by the results of some initialization scripts. One of those outputs contains a hashed version of the locks pin combination. Luckily, the lock is using an outdated hashing

algorithm that is easily brute forced. This is where we need your help. The software team wrote a script that handles reading output from the PIN and brute forcing the hash. They loaded onto a Raspberry Pi, so our field operative

only has to open the smart lock and connect one wire from the Pi. He was running through a dry run today on our test locks and uncovered a problem. The Raspberry Pi input output pins can only handle 3.3 volts and the smart lock

transmits at 5 volts. The hardware team has already left for the day. We need a simple solution to shift the voltage level down from 5 volts to 3.3 volts. Our lab is stocked with pretty much any commercially available standard resistor. Oh, and one

other thing. The lock has an anti-tamper setting built in that will stop it from being able to open if it detects any output current from its microcontroller pins above 1 milliamp. Make sure your design won't trip this. The Raspberry Pi

IO has an input resistance of 50 koohms. On the next slide, I'm going to give a starter circuit for the solution and a few tips. So, if you want to go in and solve this completely on your own, then

close the video now and you can check your solution in the next video. However, if you'd like a little bit of a starter circuit and some tips to get started, I'll see you in the next slide.

Okay, so here is a starter circuit for us to put our solution in. We have the lock transmit pin. So, TX usually stands for transmit. And then we have the Raspberry Pi receiving pin. And we know that the lock transmits from 0 to 5

volts. And then we need to drop that down to 0 to 3.3 volt. One thing I want to show here is this notation that you will very frequently see where instead of writing 3.3 volt um we'll actually use the symbol for the units instead of

the decimal here. And that's just because it makes it less errorprone to reading if you miss the decimal for example especially in things like resistors. Uh so we will put the unit in the decimal and you will commonly see it

written like this. Um and then also for resistors you'll just see it as you know this K. So 50K means 50 kiloohms.

When you're solving for this circuit I wouldn't really worry too much about this section right here. Um just focus on what's here and then focus on getting you know your output that we would be able to pull off this at 3.3 volts. And

one last tip for you, don't worry about treating this challenge like it would be a high school or university exam where you're just going to have to sit down with a pen and paper and solve it. I'd encourage you to use whatever resources

you would like. So use Google. If you want to use chat GPT, give that a shot.

If you want to use Circuit Lab, then that would be definitely be a valid way to solve this. And also since we're going for a reall life solution using real life components, you won't need to get your solution to be exactly 3.3

volts output. Shoot to get it within 5 to 10% of that. The closer you can, the better, but as long as you're within that 5 to 10%, that's great. Good luck with the challenge. I'll see you over in

the next video where I'll show you my solution. Hey everyone, hope you had fun with this little challenge. So, we're going to go through a solution. Now, the first thing that I usually do when I get a problem

like this where we had a lot of wording is I'm just going to take out the key design components that are required and I've written them down. So, our key design criteria of course is that our voltage in where we're at the lock

transmission is 5 volts. Our voltage out has to be 3.3 volts. And then our current out of our transmission pin has to be less than 1 milliamp. And then finally, we have this limitation that we can only use standard resistors. And

we'll chat a little bit more about that later in the solution. So I'm going to be showing how I would approach and solve this. But as long as your solution fits this design criteria, then that is okay. You may have recalled from our

previous lecture on series circuits and kaw's voltage law that when we have two resistors in series then we actually are able to split that voltage across the two of them or as some may call it divide that voltage and this is a very

common circuit called a voltage divider. So if we're not familiar with those though what I would suggest and what I would do is I would just go hop over to Google and look that up. So let's hop over to the browser.

Just going to hop over to trusty Google here. The first thing I'm going to look up is just a voltage divider.

And we'll take a look at trusty Wikipedia here. Perfect. So, we're already seeing we got a voltage divider. And if we want to read um a little bit about it, we can do so. And then we can also see the

mathematical proof here for it if you're interested in seeing that. But we moved on to the engineering solution. So I'm just going to take a straight look at the engineering solution. Um, and I see this little circuit here. This looks

exactly like what we need. We have a voltage in. We are just using resistors.

And then we have a V out. And if we look over here at the formula, we even get this handy dandy formula here that just says V out over Vin= R2 over R1 + R2.

And we already know V out and Vin. So we can just grab this and steal it and solve for R2 and R1 and we'll be able to finish our circuit. So we saw from that Wikipedia page the layout of that

voltage divider will fit exactly as we need. Uh so I'm just going to grab it and steal it.

What we've done here is very common, you know, taking a specific circuit element or a few portions of a circuit in kind of like a block format and then using that in our own designs. And this is very common in circuit design. It's

something to keep in mind when you're either building a circuit or reading a circuit is that we don't necessarily have to reinvent the wheel. There is lots of various circuits that perform a specific small function that we can then

add together, you know, as building blocks to a bigger circuit to accomplish a bigger overall goal. If you're familiar with programming at all, this is kind of similar in that we would use, you know, libraries and pre-built functions and we would combine all of

these together. And our job as the programmer is not to reinvent the wheel and rewrite all these libraries and functions. we just kind of have to do the in between code that links all of them together. And that's the same in

circuits. With that being said, we've taken our voltage divider here and dropped it in. And we know the voltages.

We just have to solve for R1 and R2. So, what I would do first is add our current to this circuit. And I'm calling it IM for IMAX. And that's the max current that we are able to have coming out of

our microcontroller pin from the door lock. And you may recall that that was set at 1 milliamp.

Now what I'm going to do is I'll say that yes, it needs to be less than 1 milliamp. But because this is a real life engineering solution, I'm going to set it to 0.75 milliamps. And we'll give ourselves, you know, that 25% headroom

there in case we have any extra voltage or anything, a little voltage spike. we don't actually get close to um that 1 milliamp. And this is very common when designing circuits is that you don't want to go right close to the maximum

because spikes or things can happen. If we put in our equation that we grabbed from Wikipedia, of course, we have V out over Vin= R2 over R1 + R2.

Since we know the current to simplify that equation, we can use Ohm's law to actually calculate what R1 and R2 are together. So of course using Ohm's law reminder that it is V= IIR. In our case that's going to be 5 V = 0.7 milliamps *

R1 + R2. If we rearrange that a little bit we'll get R1 + R2 = 5 V over and you'll see here I have written it as 0.0075 amps. So, I'm just converting from milliamps to amps because if you're

actually doing this in your calculator, these are the actual numbers you would need to punch in if you want to get your resistance in ohms.

So, we get that R1 + R2 = 6.7 kiloohms. And now we can drop that back into our initial voltage divider equation.

So, I'll just clear the screen quickly here and we can drop that in. Reminder that the initial formula was V out over Vin = R2 / R1 + R2. We can start plugging some numbers in here. So we have 3.3 vol / 5 volals R2 / 6.7

kiloohms. We're substituting there the R1 + R2 with the 6.7 kiloohms that we calculated.

That gives us 0.66 66 = R2 / 6.7 kiloohms. And if we rearrange that formula, we can solve R2 = 6.7 kiloohms * 0.66, which is actually equal to 4.4 kiloohms.

All right. And we know that R1 + R2 is 6.7 kiloohms. Just a reminder from our calculation before. We can rearrange that. So R1 = 6.7 koohms - 4.4 4 koohms, which gives us an R1 of 2.3 koh.

Perfect. So that gets us very close. These calculations will give us a nice output voltage of 3.3 volt. However, unfortunately, we can't just buy or get whatever resistor values we want very easily. We are limited generally to what's called a list of standard

resistors, which are the ones that are actually commonly commercially produced. In order to get a little bit more information on that, let's hop back over to Google. So, just a quick tip on these components that come in different values

like resistors. You can get tables from the manufacturer. So, I'm just going to look up standard resistor table.

And if we scroll down here, this one here, um, they've already looked at it is from Vich, which are a manufacturer of a lot of electronic components. So, we're going to take a look at their table.

And the way that these tables work is they are a logarithmic scale. And the values listed here are in these plus or minus what we call tolerances. So if you um you know look at the values under plus 1% that means that they're

guaranteed that the resistor will be plus or minus 1% of that value. And then the values in here they can be either in plus or minus 0.5. 0.25 or even 0.1. So you can specify, you know, how exact or

precise you need it to be. Of course, the more preciseness you are purchasing, then the more expensive those resistors are going to be. And we see all these values. Like you'll see, oh, we only have like 10 ohm, 10.1 ohm. Like how do

we get resistors of different values? If we scroll down to the bottom here, it actually gives us a little bit of a reading about how that does. And it says standard resistance values are obtained from the decade table by multiplying by

powers of 10. As an example, 133 13.3 can represent 13.3 ohms, 133 ohms, 1.33 kiloohms, 13.3 kiloohms, 133 kiloohms, all the way up to 1.33 megga ohms. So the way that works is we can multiply it by 1 and that just gives us the ohms

value and then we can multiply it by 10. can multiply it by 100 um a th00and and so on. So what we're going to look for then is our first resistance value we calculated as needing uh 2.3 kiloohms.

So if we scroll down this table here, perfect. The closest one we can get to is 23.2 here. This 23.2.

And if we multiply that by 100. So, if I just open up a calculator quickly and just to show you how this works, if we go 23.2* 100, get 2320, which is equivalent to 2.32 kiloohms. So, pretty close.

We can do the same for the other one we were looking for was that 4.4 kiloohms.

So, we scroll down this one here. Perfect. We've got one that's 44.2. Um, and that's the closest we can get. And if we multiply that by 100, we're going to get 4.42 kiloohms.

So, you may be wondering that these are a little bit off of our calculations in resistance values. And that is okay.

Just like we designed some tolerance into our max current calculation, it's generally safe to assume that other circuit designers are going to add a little bit of tolerance into their circuits as well. So, for the Raspberry Pi, this means that our voltage is going

to just be off by a little bit, but that will be okay. Now that we found our standard resistor values, let's hop back over and just make sure that these still work. Okay, so I filled in our resistance values.

And just a very quick reminder on our notation here where we have filled in this 2K 32 and 4K 42. This K here is representing the point and we can think of moving it over here. So this is

actually 2.32 kiloohms and this is 4.42 kiloohms. So if we just want to really quickly do the math, of course our current is going to change just a little bit because we have changed those resistances and using Ohm's law of

course we can divide we can take 5 volts and divide it by the total resistance and that's going to give us 0.74 milliamps which we are pretty close to original one. So we know our voltages are going to be pretty good. Of course,

our V out is going to be the voltage in minus the voltage drop over that first resistor. And of course, we can use Ohm's law again. And that gives us, if we wanted to punch into our calculator, this 5 volts minus, of course, again, we

have switched back from the milliamps to the amps. If you want a quick way to do this and the way that I actually like think of it in my head is if the the decimal was here and we're going from

milliamps to amps. So millie means 1,000. Then I literally just I I draw the things. I move the decimal over three points. And that's how I do it and think about it in my head. So we punch in this calculation. We're going to get

V out is equal to 3.28 volt which is close enough to 3.3 that will be perfectly fine for our operation. So the last bit that I want to touch on just in case anyone's wondering is you know I

didn't even really touch this portion of the circuit in our solution and when I was doing the calculations and this is a tip I gave you I said just kind of ignore um this part of the circuit for

now and we'll just work on dividing our voltage here. Now, the reasoning for that is if you actually crunch the numbers here, you know that, you know, we're supposed to be 3.3 volts all across here. And if you

punch that in for the circuitry, you're going to get a magnitude of, I believe, 0.06 milliamps. So, we're talking much, much smaller um than the current that we're working with here. And this is by design on these receiving pins for devices

because, of course, we want to use as little current as possible. We're not powering anything. We're just reading the voltage. So, as little current as we can get away with, we will use. And that's how these are designed with this

really high, it's what's called input impedance or resistance. Now, if you did actually go back and, you know, solve this whole circuit out, taking into account when we hook up across this input pin, of course, that will change this current just a little

bit. Um, you know, we'll have an extra little bit of current draw by adding these two resistors in parallel. Even though we're adding a 50 koohm resistor um in parallel, it's actually going to make the combined resistance of these

two circuits smaller. So if you take the total between these two, it's actually going to be a little bit smaller than this. And of course, that's going to increase our max current just a bit. But luckily, we left a lot of headroom in

our calculation, giving ourselves that extra 25%. And that's going to be okay. So just to really quickly show how that would affect the circuit if we do take into account that input resistance I've added it here and just to show another

very valid way of solving this problem I've quickly sketched up our circuit in circuit lab and I did drop in those resistance values that we were using. So we check this node we have 5 volts as expected and our total current has gone

up to 783.6 micro amps which in milliamps would be 0.78. So, we're definitely still below our 1 milliamp. Of course, cuz we've increased that current, we're going to have a little bit more voltage drop over this resistor. If we look at the voltage

down here, we can see that it is 3.18 volts. And that is a little bit below our desired 3.3 volts. So, if you did take this into account and you were able to find standard resistors that functioned a little bit better in this

scenario, then good for you. However, that 3.18 volts is well within the threshold that we would need for a logic shifter. Uh, and we're going to talk a lot more about digital communications in further lessons, and it'll make sense

why we can be off by that um, you know,.12 volts. We're only off by about 4%. Which is okay. Finally, one other point here. If you use resistance values that are much greater than this, that's okay. And honestly, it may even be a

better solution because we're going to reduce our overall current draw, which of course is going to lower the amount of power that we're pulling um from the smart lock. So, that actually may be a better design. I just went with the

lowest number that was underneath our max current. That gave us a little bit of threshold, but you know, you could even increase these even more as long as you use standard resistance values if you wanted. Um, as long as you're

getting that 3.3 bolts here, then that would be a valid design solution. If you got the solution, great job. That's it for this first section of the course and I'll see you over in the next section where we're going to start with some

hands-on. I hope you're enjoying the course so far. A really quick reminder to make sure you are subscribed to my YouTube channel which is linked down below. And also make sure you are subscribed to the TCM YouTube channel where you're

watching this right now. We're almost at 1 million subscribers as I'm recording this. It would be great to hit that mark. So if you are enjoying this video and you've watched to this point, it would really help us if you could

subscribe. Hello everyone and welcome to the second section of the course where we're going to be doing some hands-on testing and a little bit of hands-on lab work with some of our equipment and the router that we're going to be targeting.

Before we dive into these hands-on portions though, I want to do a very quick and very important lesson on electrical lab safety and some of the dangers of working with electricity. As I'm sure everyone watching this is aware

that electricity is can be very dangerous and can also be deadly. However, the things that we're going to be working on in this lab and the testing that we're going to be doing can all be done extremely safely. And in

order to do that, we just have to follow a few very simple rules. So the first rule and if you're only going to listen to one or follow one is this is the most very important one and that is that we're only going to work on

low voltage. So what does that mean by low voltage? Well, a good rule of thumb is generally to stick below 30 volts DC.

That's a pretty common standard for what's considered to be the threshold of low voltage and safe voltage to work at without further proper training on how to handle high voltage. So that means that we're not going to be working on

anything with the wiring or the outlets or anything like that from our household. In North America, our household voltage is 120 volts. And depending on where you are in the world, that may differ. You might even be up to

240 volts or 220 volts. So all of that is outside of that safe range. So we're not going to be touching any of this stuff. We're going to leave that to the electricians. uh all the wiring behind it and that also includes anything that

we plug into it. So in our lab we're going to be using the power supply that comes with our router and of course when we plug it in at this end it's 120 volts and then it gets stepped down to 9 volts

for us that we're going to work with. But since this whole thing plugs into the wall, that's all we're going to do with it. We're just going to plug it into the wall and into the router. We're not going to open this up. We're not

going to do any testing on it. We're not going to modify it. We're not going to alter it. Also, if we do come across a power supply that we're using, it has been modified or altered or we see that

it's damaged, we shouldn't use that. And in addition to that, we should only be using the power supplies that are rated for the equipment that we're using. And the best bet to make sure you're doing this is to use the power supply that was

included with the equipment. So, just a really quick demonstration of why it's so important for us to leave these higher voltages to the pros. I just want to go over a chart here that shows some of the effects of electrical

current on the body. And when we see this current, so this is not um like the supply current that the circuit can actually supply. This is, you know, if we were to uh shock ourselves, this is the actual current that would run

through our body. So you'll see even at 1 milliamp, which is a fairly small current level, we'll start to be able to notice a slight tingle. Even at 10 to 20 milliamps, this is where we'll lose the um our ability to let go. So if you

know, you were to grab a wire or something like that and you're getting electric shock, uh the current is actually strong enough that it will cause the muscles to contract and we can't let go, which can actually be

quite dangerous if we aren't able to let go. We'll be continue to receiving that shock. um at 30 milliamps breathing can become difficulty and we start getting you know the increased possibility of death and then once we get to even 100

milliamps so this 100 to 300 milliamps is when ventricular fibrillation happens. So this is when um the electrical signal through our body actually is able to shut off our heart.

So like very dangerous and um likely fatal. And then above these levels you're going to get into like really severe burns and lots of nasty stuff. So as I mentioned before this current though is the actual current through the

body. Now we know from our previous lectures of course that the current is dependent on two things. The voltage and then the resistance. So in our case we can control the voltage. That's why we're only going to be working on these

low voltage levels. Um and then the other thing that we do have working in our advantage is especially at lower voltage levels um the body has a very high resistance level. So, just to demonstrate that, I want to show like a

really bad stick drawing I have here um of our little demo person. We'll call him Bob. And Bob has was working and he was working overhead. Um so maybe he made contact with his hand to a live wire that he was working on overhead and

then he had his other hand touching maybe a ladder um or a railing or something metal. So he's created a path for the electricity to travel through his body and to ground.

Now we'll say in this scenario Bob has you know dry clean hands without any sores or anything like that on his hands and under that scenario the resistance of the human body and the skin particular is very high. So 100 kiloohms

is a pretty good estimate for dry undamaged skin. And if we do the really quick math for this using Ohm's law of course the current is equal to the voltage divided by the resistance. So, we get 9 volts over 100,000 ohms, which

we get 0.09 milliamps. So, Bob wouldn't even feel this one. And that's because we're working with a low voltage level.

And also, we have this dry, clean hands. However, if we just change this up a little bit. So, a more likely scenario, if he's working at his home or something like that, we have now 120 volts. So, also we'll say that his hands are sweaty

because it's been hot and he's been working. And under these conditions, the resistance of the skin is actually much much lower. And we'll estimate for this case that it's down to 1 kiloohm, but it can even get lower than this. So if we

recrunch these numbers now, under this circumstances, we can see that we're actually already up to 120 milliamps. So we're well within this fatal zone. And that's why it's so so so incredibly important for us to leave these higher

voltages to the pros and only work on the lower voltages. In this course, we're just going to be working generally around 9 volts, which is the what comes out of our power supply. Um, we're not going to be working with that power

supply at all. We will plug the power supply into the wall and then we'll plug the power supply into the router and we will be working only on the router. The second rule that is just a really really

good habit to get into is that we're only going to power on circuits when required. So if we need to test them, then we'll power them on and then we'll power them off. And if we don't need to

actually, you know, be doing any testing that requires a circuit to be on or any work that requires a circuit to be on, then we'll just power the circuit off.

So at some points in this course, we're going to have to connect things. is we're going to be visually inspecting the board. And at those points, there's no reason for us to have the board on or the router powered on. So, we will power

it off. And the best way to make sure that you actually have it powered off is we will just physically unplug the power source. So, in our case, it is this brick power supply. We're going to unplug that right from the router. Our

router doesn't have an onoff switch, but some devices do. Um, even when they do have an onoff switch, my in my opinion, best practice is just to remove the power supply and then you know there's no chance of uh accidentally having any

electricity coming through to what you're working on. This is just a really really good habit to get into when working with any type of electricity. It can prevent you from getting a shock and also can prevent you from damaging the

board. So I always get in the habit I'm done working with it, turn it off. If I don't need it turned on, I don't even turn it on.

Okay, the third rule, a really quick one, is that we're going to remove any jewelry. Uh we were talking about how the resistance of the human body is quite high. So that helps to us to prevent from getting these damaging

electric shocks because we keep the current low due to that high resistance. Of course, metallic jewelry is a very good conductor generally. So it can actually carry quite a bit of current.

And what can happen if you make contact with any jewelry even at lower voltages?

uh it doesn't increase our chance of a shock because that resistance is still high on our skin. But the jewelry can heat up quite hot and you could burn yourself. Um or you can make a spark or something that is a distraction to you

and causes you to do something else that would be dangerous like swing your hand away and hit it on something. So good rule of thumb really when you're working on anything but especially electronics we should remove any jewelry.

Okay. Okay. And then the last rule that I want to chat about which is not as applicable for this course but just in case you're going to go um and take what you learned in this course and work on

other electronics and that rule is to be mindful of capacitors. So we haven't chatted too much about capacitors yet and we will talk about them much more in detail in the 2011 section of electrical engineering for hackers. But just a

quick rundown on capacitors. They are able to store an electric charge on a circuit kind of in a similar short-term way that a battery would do. Um, and they're actually able to build up a much more powerful charge over time. Um, and

then dissipate that very quickly. And with larger capacitors like some of the ones that are shown here, they can actually be at a much higher voltage than the rest of the circuit operates at, and they can pack a pretty good

punch. So, if you're not careful with these guys, you can get a good shock and actually at levels that could possibly dangerous. The other last really important thing to keep in mind with capacitors is that they are able to

store charges. And some of these capacitors can actually hold onto a charge for a pretty decent amount of time. So this means that even if you're, you know, following rule number two and we've powered the circuit off completely, you've removed the power

supply, the capacitors can still hold a charge for a pretty good amount of time.

Um, good circuit designs will have ways to dissipate this uh over time. However, you don't want to trust that someone has put this in. So we always want to be mindful of discharging these capacitors.

How to do that is a little bit outside of the scope of this course since we're not actually going to be working with any capacitors that are at that dangerous level. So, if you do encounter these large capacitors when you're

working on something, you know, even in TVs or power supplies for computers or things like that, be very careful of them and maybe do a little bit more further research or learning before you actually dig into using them. Again, in

this course on the router that we're using, there's not going to be any that are at that high dangerous level. Um, but I just wanted to make sure everyone was aware of that. So, that wraps up this quick lesson on safety. I will see

you over in the next lesson where we're actually going to start getting our hands dirty and do some hands-on.

Hey everyone, welcome to this first handson lesson of the course. If you've just unbox your router, one really quick reminder to hang on to the uh plastic twist tie here that I have. It's what holds the power supply together. And

we're going to be using this guy later on in the course for a little bit of a hack to get a connector connected without soldering. So, make sure to hang on to this. Just set it off to the side

and hang on to it. So, in this lesson, we're going to be taking a look at our TPLink router.

That's going to be the target that we are hacking on and doing testing on throughout the course. Now, the one that I'm working with and the model that we're going to be using throughout this, if you just want to double check, it is

a TLWR841N. And I've chosen this model to be our target for a couple reasons. Um, one of the main ones is it's very cheap at about $20. And it also has a lot of what some people will call features. other

people would call um security misconfigurations that can help us to learn about hardware hacking and some of the things that we can take advantage of.

Now, in order for us to get access to most of these hardware hacks or any of the testing, we're actually going to have to open this device up. So, we're going to be in this video taking a look

at how we can do that. In order to do so, we are going to need a couple of tools. So, one of them is going to be a Phillips screwdriver. I've just got a set here of small um screwdrivers, which

includes a Phillips screwdriver. And then we're also going to need something to uh pry this open. So, I've got two here, what are called spudging tools, and they are used to pry open uh electronic devices like this. Now,

you'll see this in many electronic devices where it uses what's called uh a pressure fit to snap together. So, this one's got a couple screws in the back, and I'll just flip it over to show you that right now. So, we've got two screws

here in the back. And once we take out these screws, though, it's still not going to come apart. It's actually going to be uh held together pretty tightly.

And the reason for that is most of new electronic devices these days use this pressure fit. So, even things like your phone, if you've ever had to take that apart uh to get your battery out, or laptops, they use this pressure fit.

And these spudging tools are specifically designed to open that. Um the nice thing about them is they are also not conductive. So we don't have to worry about um any type of shock discharging into our components or shorting anything.

Picked these ones off off up off Amazon for pretty cheap. Um but if you don't have any or don't have access to them, you can use a small flathead screwdriver. So I've got one right here.

The only thing with these is to keep in mind they are metal. So, we don't want to make sure we're not shorting um any of the circuits. So, try and be careful when we are using them um not to insert

them too far into the router themselves. Okay, with that out of the way, let's take a look at how we can open up this router. So, the first thing to do is just to pop these screws out. So, I'm

going to do that right now. if you haven't done so already. Also, these antennas just fold down. It's much easier to work with them if you fold them criss-cross like I have here. And we'll just take these screws out.

So, even with these screws taken out, you'll see um the router is still actually together pretty strong. Even though I'm pulling on it with my hands, I can't quite get it open. So, this is where that spudger tool comes in handy.

On this router specifically, I find it's easiest to, if I just move these antennas out of the way for a second, it's easiest to get started. We can uh kind of slide in here with your tool and pry open. So, that's where I am going to

start on mine. And if you just get the tool in and just give it a little pry, you can see mine has popped right open.

And I still have it. It's a little bit stuck on the ends. Um, here I'll I'll flip it up so you guys can see. Still stuck here on the end. So, this is where this tool comes in handy. Can just try

and pry along. If I just use my hands a little bit. We can just work it along the edges.

I'm going to come back to this side here. There we go. Okay. So, the one thing you will notice when you're doing this, and you may have heard it there on camera, um, is we do get some kind of snapping, and it does

sound like it is breaking a little bit. That is to be, um, expected when you are working on these pressure fits. That snapping is okay. Uh, you'll notice like nothing on here actually broke. I've got no broken plastic. And if I wanted to, I

could just snap this back together by just pushing it uh back together. Just going to set this out of the way here.

All right. So, we now have our router open and we can start taking a look at working on the internals. I'm going to pause this video here and we'll pick up in the next one where we start taking a

look uh at the internals and we'll also chat about how to safely handle electronics and make sure that we don't have any electrostatic discharge. That wraps up this video. I will see you over in the next one.

Welcome everyone. So before we start actually touching and handling and testing our router and the internals of it, I do just want to chat a little bit about electrostatic discharge and how we can safely handle the electronics and

the PCB. So I'm sure that everyone watching this video has at some point in their life walked across a carpet or some other surface and then touched a doorork knob or another metal object and received an electric shock. And while these shocks

are not harmful at all to humans, while they may be a little jolting or surprising, they're not actually harmful to us, they can actually be very harmful to electronics and in particular the kind of very small electronics that we

see on these circuit boards. Now, the reason for that is with an electric shock, you can actually get up to easily 5,000 volts or more. The reason they're not dangerous to humans is, of course, it's for a very, very, very short amount

of time. So, the amount of energy dissipated is extremely low. The reason this isn't harmful to humans is that it's for such a short period of time, and our large bodies are easily able to just dissipate any of the charge that

would come from that. However, for small components, if I just grab my pointer, um like some of the ones on this board here, like the chips or the other, um it's even really hard to see small componentry on here. They're so tiny

that this large uh charge across them can actually do quite a bit of damage.

The one really concerning thing with electrostatic discharge or shocking these components is that a lot of times the damage won't be noticeable right at the start and everything will function as is. However, we've weakened that component um to the point where it's

going to fail later on. And this can be a nightmare from a quality assurance standpoint, especially if we're working in a production environment or we're doing testing on a board for a potential customer or something like that. We want

to make sure that we're not accidentally introducing this damage to the board because then we're not entirely sure if it's something that we did legitimately with our testing or if it's from this electrostatic discharge.

So, if you're working in a professional setting, depending on where you're working, there's going to be a set of measures that you're probably going to have to follow for electrostatic discharge and to make sure that that doesn't happen. And I just want to go

over some of those so that everyone is aware. And then when you're working at home, you can kind of make your own risk assessment about which ones you're going to follow. You know, one of the nice things in this course is the router that

we're working on is relatively cheap. It's only $20. So if we do damage it, then it is easy to replace. And you know, in this scenario, we're not actually um working on a customer's component. So ultimately, it is up to you to decide

how many ESD precautions you want to take. These are not like a safety precaution for ourselves or injuring ourselves. they are to stop us from uh damaging the board and our equipment.

All right, so the first thing that I'm doing here is I'm actually working on this um ESD mat. So the way that this works is it's very insulating. It's made of rubber and it has an extremely high surface resistance. Um so that's going

to help stop dissipate any electric shock because of course it's going to be hard for there to be a path to ground.

Another thing that we can do before we start working is we can make sure to dissipate any charge on our body. So, what I have done is near me I have a doorork knob that's just off camera that

I touched before I start working. So, if you have anything similar near you, a doorork knob or like maybe a metal bed frame or anything like that, you can make sure that you've dissipated any of your charge.

The other thing that we can do that is free is make sure that when we're handling the board, we're not actually touching any of the components unless we absolutely need to. So, if I were going to pick up this board, then I would do

so from the edges and just touching the edges like so. Um, I wouldn't like actually go and directly touch any of the components because that can relate to a shock going straight into the component. It's why like when I need to

point out to them, I am using um this tool that is nonconductive so that there is no chance of dissipating shock.

Okay. So, the other things that I'm going to show here are stuff that's going to cost money. And I'm not going to be using them all cuz I personally feel like it's a little bit overkill for this, but I just wanted to um

demonstrate in case you are ever in a professional environment, you'll probably need to use those. So the first one is something that you've probably seen and that is these ESD bags. So these bags are non-conductive. They're highly resistant and when we're

transferring or moving electronics then we should put them in these bags because it stops uh any electric shocks from dissipating throughout them. So these are great for that. You've probably seen them if you've ever bought like any electronic components. They come in

these bags. The other thing that you will commonly see in a professional setting is a way to actually keep yourself grounded. And I'm just going to show you one way that you can do that.

So, I have a power bar that's mounted that I'm using for power. Um it's just right here. And on this power bar, of course, um this little pin here, this is just a straight connection to ground. Um so that's generally done for safety

reasons. If we have a short circuit or anything like that, um all the power will go straight to ground. And this plug that I have here, it's only got one prong and it only just fits into the ground. Um, so I'm going to plug that

guy in here and then it's going to give us access here. I got it plugged in and I'll just set that here. It's going to give us access to two ground connections. So, what I have here is a wristband and this is a metallic

like it's got metallic conductive material in here. Um, and it's got this alligator clip here that I can pull off.

So, this plugs into one of these guys. And then I can just put this wrist strap on.

All right. So, you just wear it on your wrist like that. And then this, what this does is this makes sure that I'm not actually going to be able to build up any charge because I am constantly grounded. So, there's almost like a zero

resistance path for any charge to go. And it's going to take the path of least resistance. So instead of, you know, shocking anything, it's going to go through to ground. All right. So I'm just going to take this off cuz it's a

little hard to film with and I'm not going to be using this because I think it's a little overkill for this lesson.

But if you're in a professional setting, like when I used to work on electronics in a professional setting, I would wear one of these.

All right. And then the last thing that you can do um is that we actually can ground the work area that we're working on as well. So I've got another one of these clips right here. And we've got this that

plugs in on the one end and then it's got this alligator clip here. Um, so I'm just going to clip it onto the side of this mat.

And then even though this is set to be like a really bad conductor, um, and it's very very highly resistive, just in case, we can also ground this to make sure that there's no chance of any, uh, electrical charge dissipating. It will

go straight to ground. Um, okay. So I just plugged that in. Again, I'll show you into my power bar that's here. So now if I'm wearing this, I'll just put this back on again quickly.

All right. So if I'm wearing this now, we can see that um you know, I'm grounded and the area that we're working on is grounded. So it's it's almost impossible for us to have um any sort of electrostatic discharge.

The last thing that you'll see um in a professional environment and is something that I have had in working areas as well is there will also be special flooring that is very very conductive so that it makes a good path

to ground and you'll wear special shoes that are ESD protective shoes and they will also um make sure to ground you. So we're then have three points of grounding and it's very unlikely that we're going to have any sort of ESD.

Now these last three things where we're using, you know, the grounding of the mat and the grounding of the um wrist strap, and obviously no one's going to have this at their home, but the grounding through the shoes are great

for production environments and we want to be absolutely sure we're not going to do any damage. Um, however, for the home stuff, I would just suggest to, um, sticking with the, you know, touching only the PCB by the edges and trying to

avoid actually physically touching any of the components themselves. And I also do just ground myself on something metal because it's very easy to do um, before I work with it. That being said, if I was working on something like my

personal laptop or maybe my phone or something that was worth a lot more money, then maybe it's good practice to follow these. So, I will leave that up to you as the viewer um to choose which options you're going to use for PSD

protection. With that being said, we can now move on to our first testing and taking a look at the PCB. So, we'll wrap that up for this lesson and I'll see you over the next one.

Welcome everyone to this lesson on PCBs. So, if you're not already aware, PCB stands for printed circuit board. And in the internals of our router that is this green board here.

Now you hear PCB used interchangeably to reference both just the bare board. So that is just this green portion of the board and then also what is called the PCB assembly which is actually the bare board. Then with all of the components

that are soldered and attached to the board. So, generally when people are talking about PCB, they'll use it interchangeably and they'll just call it the board or PCB. Um, and most frequently that will refer to the actual whole board itself, including all of the

components on it. I'm going to move our target router to the side here and show you an example of just a bare board so that we can look at some of the features of it.

So, this is called a helping hand. It's just good for holding electronics in place. I'm going to use it just to hold this board a little bit closer to the camera. All right. So, the PCB has two main functions. The first one is that it

holds all of the components in place. And it does that by we have these um items here. So, here and here and here.

And there's many of them on the board. And these are called pads. And the components like the resistors and the chips all get soldered to these pads and that helps hold them in place. So on this PCB we actually have two different

types of pads. The first one are is example is right here and these are called through hole and the reason for that is these are actually uh a hole on the board that have a metal ring of conductive material and the components

actually go through this hole and then are soldered in place. So you can see I don't know you can see I can actually poke the can actually poke through it here. The second type of pad that we have are these example right here. So we

have many of these ones as well. And there's no hole here. We just have a metal rectangle of conductive material.

And the components don't have any leads. They just get soldered directly onto these pads. And that's called a surface mount pad because the components are directly surface mounted on there. So I'll just flash up on the screen here

quickly to show you an example. On the left here, I have an example of a through hole resistor. These metal wires on the sides of it here are called the leads. And you can see here an example of it on the board. So the leads will

actually fold. These would be holes that they would slot through. So you can see some examples of those holes right here.

You push the leads through the holes and then they get soldered in place. That's why it's called through hole. And then on the right hand side, this is an example of a surface mount resistor.

Instead of leads, we just have these metal edges that are on the sides of it.

You can see here on the board, they actually just fit onto those pads that we were showing, and they get soldered into place that way. And there's no holes or anything. In commercial boards these days, you're going to be much more

likely to see mostly surface mount components. And there's many reasons for that. One, they can be made much, much, much smaller. You will see that on the actual router board. And then second, it's much easier to automate the process

of creating these boards. We can have machines much more easily drop these into place instead of having to bend the leads and push them through the holes.

And we'll take a closer look on our target PCB of the router as well at how those look. The second function of the PCB is that it actually electrically connects all of the components together to form the actual circuit. And the way

that it does that is with these green lines that you can see uh drawn on here.

So these are what are called traces and they are electrically conductive and they perform the function of wires on the PCB. For us as hardware hackers, this is quite important because we can actually start to visually inspect the

PCB and try and figure out what the circuit is doing and where the signals are routing on the actual PCB. One thing that does make this tricky though is that modern TCBs now have many layers to them. So of course with these traces for

example like these ones we're not actually able to uh route through them. So if we wanted to cross through here for example we cannot route through these traces. So what we have done in modern PCBs is we actually make them

multi-layer and that way we can have traces buried in the middle of the PCB and we can also have traces and components on the back. So I'm just going to quickly flip this one over to show you how that looks.

Okay, so looking at the back of this PCB, you can see that we actually have some traces that are just visible on the back that are connecting um some of our pads. And we also, for example, here this F1, this is a fuse. So we can see

that it actually uh is only on the back as well. And then the last thing that I want to show here that is really important and unfortunately makes our lives kind of tricky as reverse engineers is we can see that we have

this D1 here. So, diode one. And you can just make out the traces here, but they don't seem to go anywhere. They just go to these very tiny metal holes that are not actually uh through hole pads. And

if I just flip the flip the PCB back over. So, if you just keep in mind where this is on the PCB. So, when I flip it over, can see now this is where that was. And there's no traces or signs of anything.

And we only just have these two metal holes here. So what these are called is they're called VAS. And VAS we can think of as traces that go between the layers.

So they actually um take the trace and then they transport that electrical signal. So these have conductivity and then they go to layers. So on this PCB that diode's traces, they actually go up and only into the middle layer of this

which we're not able to see. So that does make it a little bit more challenging for us to reverse engineer.

However, there are ways that we can get away from this. So just to demonstrate what the VAS look like, I'm going to pop up on the screen here a quick image and chat about them briefly so you can see

uh in 3D what they look like. On the left here, I have a sample PCB where we can see in the top we've got the assembly. And then on the bottom, just to show what it would look like

without the components soldered on, we can see just the bare board with the pads. Now, on this board, we have some VAS as well. So, we got a few VAS here, and you can see what those look like on

the bare board. So, what this would look like if we just do a break apart of this into kind of a 3D look, I've done a drawing. These aren't actually like all of the traces that you'd see on this

PCB, but just to give you an idea, the VAS run down between the traces. So, there's an actual like metal connection, like metal pipe, you can also almost think of it, and it brings those connections from one layer down to the

other. And then we can route these circuits. So, this one I've drawn with three, but we can get many, many more layers in actual production PCBs.

Okay, so we're back here with the target router PCB and I'm just going to lift it out of this bottom part of the enclosure. So, it can just lift right out. There's nothing that's actually holding it in. It's just resting on a

couple of pegs here. All right. So, I'm just going to lift it out. And then the only thing that's actually uh attaching it is these wires which go to the antennas. So, if we're just gentle, we can lift it out though to work on it.

And what I'm going to do is I'm just going to quickly put it on the helping hand so that we can get a closer look at the PCB itself.

So, unfortunately, our target PCB is a little bit more complex than the one we were just looking at. But in case you're getting intimidated by taking a look at this, do not worry. We don't actually need to know everything about this or

how it works, there's just a few key points that we're going to start taking a look at and learning to identify that are going to help us along our journey with hardware hacking. Now, the couple things I just wanted to show here are

we're on this board. we are mostly surface mount components and they are so tiny on this board that it is actually very hard to even see some of them uh even on this 1080p camera it's hard to get them in focus of course so we've got

our chips here and they are surface mount they just rest on top and then they're very hard to see but all of these little items here are actually components so we've got capacitors uh resistors all tucked in there in their

little surface mount packages Here's a couple that are bigger. And it's really really hard to show these cuz they're they're so small. I'll just put my finger in for reference so you can see like I could fit almost all them on the

tip of my finger here. Now, we do have a couple throughhole components. So, we've got um these LEDs here that are through hole and then our capacitor that's through hole. And generally things like, you know, your push buttons and these

Ethernet ports are also throughhole. And the reason for that is one of the advantages of through hole components is they actually hold things in place much better. So for bigger items that might be able to get bumped or we're going to

be plugging them in and out, you'll usually see through hole used. And I'll just quickly flip the board over so you can see what that looks like on the back.

So you can see on the back of this, this is actually where these components, their leads stick through and they are actually soldered through those through holes.

That wraps up this first look at PCBs. I'll see you over in the next lesson where we're going to break out our multimeter and start doing some testing on our PCB.

Welcome everyone to this video where we're going to be chatting about digital multimeters. I've got the one here that we're going to be using in the course and in this video we're going to be taking a look at it. So digital

multimeters are arguably one of the most important tools in both an electrical engineer and hardware hacker's toolkit.

And the reason for that is they are kind of like a Swiss Army knife. They're called a multimeter because they actually perform the function of what used to be multiple meters. So in order to measure voltage in the past we used

to use what was called a voltmeter. And to measure current or amps we use what was called an ampmeter. And then to measure resistance or ohms, we would use what's called an ometer. So these digital multimeters are able to combine

all of those measurements plus a couple other functions that we're going to chat about in this video.

So this meter that we're using in this course, I've selected because it is relatively inexpensive while still being quite accurate and having some great features to it. And it has all the features that we're going to need for

this course. The one thing that it doesn't have, which you will start to see on more expensive meters, is what's called either auto ranging or autoscaling. So, what that means in that we don't have this auto ranging or autoscaling is that

we actually have to pick the scale that we want to measure on. Um, so I'm just going to pick this up to show an example of it. All right. So, if we take a look for example here, um, we can see how we

can make the ammeter measurements. So, this a symbol stands for the ammeter. And then we already know that this symbol here is for direct current. And if we want to make a measurement, for example, that is in the 0ero to 2,00

micro amp range, then we can use this one. And then if we're going above that 2,000 micro amps, and we're at this 20 milliamps or below, so between this 2,000 micro amps and 20 milliamps, then we would use this measurement. And then

so on all the way up to the 10 amps. So same thing down here, we have the ohm symbol. So this is where we can use it in the ometer mode to measure resistance. And we can measure the

resistance all the way from you know 1 ohm up to 200 ohms here from 200 ohms to 2 kiloohms and then all the way up to the 200 megga ohms. Okay. So for voltage we are up here and this is the symbol

for volts DC. Again same idea with those ranges. And then finally I'll just show you here the symbol in these two measurements. So these are for measuring um volts and alternating current. And we're not going to be touching those in

this lesson, so no need to use it. So to make measurements with our multimeter, we are of course going to need probes. And these are what are called the probes or sometimes people call them leads. And the way that these

work is we're able to press these metal leads onto the components or wherever doing our testing and we can make a measurement. And then of course the other end of them. So these ends actually plug into our meter.

The first one that plugs in, and you guys can do this if you're following along, is the black one, goes into this one, which is labeled comm. And that comm stands for common ground. So this is where the ground goes. And of course

our black is going to be that. So I'll just plug it in right now.

All right. And now you will see that we do have two areas where we can plug in the red one.

And if we look at the first one, it says here volts, ohms, milliamps, and then this squiggly line, which is for our function generator, which is another feature that this multimeter has. And that's where we're going to be using it

for this course. However, just so you're aware of why we then have one here that says it's for measuring 10 amp max.

The reason for that is we see here it says fused. So internally on this multimeter, there is what is called a fuse. And what the fuse does is it protects the internal circuitry from if we uh measure a current or something

that's going to put a current too high through the internal circuitry and it would damage that. Instead, we have the fuse in line and when that current that's too high goes through the fuse, it will burn out the fuse and stop the

current from flowing. And the fuses are really cheap. It's easy to replace them so we don't actually break um our internal circuit or burn it out. Now the fuse for this one is fused to allow the um milliamps. So we can see here if you

take a look closely this one is fused at 500 volts max or 500 milliamps. Uh so for everything in this course that's going to be perfectly fine for us. However, if you were you know doing this 10 amp current reading

here on the ampmeter section you would need to unplug from here and plug into this one. And then we get access to that bigger fuse that's going to allow that measurement. Again, we're not going to be working with anything that high in

this course, so we don't need to do that. We can just plug it into this one.

I'm going to do that right now. Plug the red one. All right. And then you can just leave it in these two for the rest of the course. That's all we'll need.

Two other features that I want to show on the front of this. So, we do have a light here. Now, if I just turn it on here, and then if we push this, then we get a light that lights up. The other

thing that we have is this button, which is a hold. So, if you're taking a measurement um and you just want to not have to write that down or remember it for a second, if you push this hold

button, then instead of measuring anymore, it's just going to lock what's on the screen. So, you have that saved.

Last thing I'll show is on the back, it actually does open up. So, internally of this, there's a 9volt battery and that's what used to power this. If it does die or it stops working, that's where you replace this. And also, the fuses are

internal in here. So, if you ever blow out a fuse, you can replace it from in here. All right. Finally, one last thing. So, you might hear the digital multimeter referred to as DMM, that abbreviation for it. And I might say

that a few times as well, cuz it's pretty common to hear that. So, just want to make sure you're aware of that.

That wraps up this video and I'll see you over in the next one. Welcome everyone. In this video, we're going to be taking our first measurements with our multimeter on the TPLink router board. However, before we get started with those measurements, I

just really want to quickly show you something important uh and another very important tool, and that is our notebook. So, in this course, I'm going to be taking notes in a paper notebook.

And this is what I usually do when I'm working on electronics because I may not always have my computer handy. And sometimes I find it very useful to just have a paper notebook because you can also draw circuits or other just quick

memos in it. Now, I apologize for my very bad handwriting. Uh, but I want to just quickly show you what I have started with writing for notes for so far what we're testing with this TPLink router. All right. So, I've put the

target here and I've got the router model number and the name of the manufacturer here. So, we have this TPLink TLWR841N.

And then also very importantly, I have the serial number here. And this is important because if we're testing multiple routers or multiple targets of the same one, then we need to identify what the actual one that we are testing

on in case we do any damage to it or something happens, we can actually trace back with our testing and see which model and which actual serial number to trace back to that physical piece of equipment. I've also included dates. So,

I'll be adding these dates in as well so we know when we're doing certain things.

And I have the first action wrote down here. So, the first thing that we've done is open up the router case with the spudger and visually inspected the PCB.

And now, as we do more testing, I'm going to be adding these actions and taking notes in here. So, feel free to take notes however you would like. If you prefer to take it, you know, in Oneote or Cherry Tree or some other type

of digital note-taking app, then go ahead. That's totally acceptable. My preference is just to take these paper notes when I'm doing the measurements.

All right. So, we'll be coming back to this throughout the course. And then we'll also be visiting these notes when we write up our final report. Just going to put this out of the way and then grab the things that we're going to need for

taking our first voltage measurements. Okay, so to take our measurements, we are going to need, of course, the router with it opened up cuz we're going to actually need to be probing internally on the board. We're going to need the

router plugged in for this. So, we will need the power supply. And then we're also going to, of course, need our multimeter. A quick reminder on safety that we're just going to be plugging in the power supply when we need to and

then we'll unplug it when we don't need it. Just to quickly show you where we're going to be measuring. A lot of times on these boards, if we're measuring the throughhole components, which is what we're going to be starting with, it's

actually easier to probe them on the bottom. So, I'm just going to flip this over. It just lifts out like this. And then we can flip it over.

And if we look at the back, we can see again like we identified before, these through hole components. And that's where we're going to be doing the testing. Now, I'm going to be using what's called a third hand to hold this

up. And it's just a little bit easier to film. You don't need to use one if you don't have one. You can just rest it on the router case like this and do the probing as well. So, I'm just going to

quickly set up that third hand. And then we'll jump over to testing. I've got everything set up now. And just to show you before we plug it in, the first measurement we're going to be taking is to verify the input voltage. And this is

something that is always good to test before we do any further testing. Now on the router here, we know we have this input jack right here. So right here and this is where the power supply plugs in.

And then it is a through hole component. And these are the two pins that come through and are soldered. So we can test the voltage by measuring the drop across these two pins. And on this router, I already know this is the positive one

and this is the negative one. So we'll put the red lead here and then the black lead here. And that's how we can test.

and I'll show you how we can how we could figure that out. All right, so I'm going to get the meter set up first. All right, so since we know that we are at looking around 9 volts, I'm going to set it to this 20

volt DC setting that I have uh here and we can use that for measurement. And I think now that we know where we're probing and we have our meter set up, we can plug it in.

Okay, so just a little bit out of the shot here, but I can see the lights are starting to light up. Perfect. So I know that we have the power on and we're ready to take our measurement.

Move this here so it's a little bit more visible. And red lead goes to the top one and black lead goes to the bottom one. And we just press it there.

All right. And we see it stabilized there at around 9.25 9.26 volts. All right. So if we had them backwards and we So we just want to identify what it would look like if it's backwards. Um, if I do put the positive

or the red one on this the wrong lead, then we'll see that we actually get a negative measurement. So, that's how we can tell which one is the positive and which one is the negative. And that's important because on this circuit, all

of our return current is going through this negative end. And we can think of that as being the ground. So, we'll come back to that later.

So to take these voltage measurements, what we did there is we actually connected the digital multimeter in parallel to make these measurements. And just to make that a little bit more easier to read, I'm going to move this

uh third hand out of the way and I'll show a quick drawing of the circuit.

All right, so I've got a drawing here just to quickly illustrate how we're taking that measurement. Now, I've got right here a bad drawing of that input jack. We've got the positive and negative leads of it and then it flows

through and into the rest of the circuit. Now, what this is called or how I'm representing this is a blackbox equivalent. So, we don't care necessarily about what's in that circuit at all. I'm just showing that, you know,

the power or the current flows through out of this jack and then it goes through to that whole rest of the circuit, which we don't care about. Now in order for us to take the voltage measurement in parallel what we did is

we attached these the probes to if we can think of it sorry this way these ends and took that measurement and now if I just set these down to kind of illustrate what we've done when we do that test is

the power is able to split that's why it's in parallel so our current comes out of the positive end and it can split at this node of course and go through our meter And then also most or if not

almost all of the current goes to the router circuit. And that's how we take that measurement in parallel for measuring voltage.

When we are measuring voltage with the multimeter, it has what is called a very very high input resistance. So the resistance internally that's making this measurement is very very high. And what that does is that it allows us to not

affect the rest of the circuit while we're taking that measurement because we barely take any current to measure that voltage.

For voltages, which is what we're going to be probably measuring the most on circuits, it's very easy to do. All we need to do is just find the two leads of the component we want to measure the voltage drop over, and we just touch the

red to the positive and the black to the negative, and we'll get our voltage reading. I'm going to take this drawing away and put the router board back on the third hand. And I'll give you a quick challenge to take a measurement on

your own. Okay. So, at the very top of this board beside this orange flashing LED, there is a green one that is on constantly. And if you just power it on your board, it does take a few seconds

for it to come on constant like that. But what my challenge is or what you can pause this video now and do is try to take a voltage measurement of this and make sure you get it to be a positive

reading. Uh just a hint that of course the leads that come through this is a through hole component. So the leads are on the back you can measure it on the back or if you want you can actually

measure it on the front. So pause the video here and find out what the voltage drop over that LED is.

All right did you get it? Let's take a quick measurement and see what I get for the reading of that voltage. Again, I've got mine set still on this 20 volts, which is going to be okay for reading

this measurement. And I'm just going to touch the two leads here. All right. And I am getting mine at 1.94 volts, which seems about right for this green LED. Again, if you flip these and put it the other way, then you're going

to see the same reading or similar reading but negative. There are a few other areas on this board where you can measure voltages.

One of them, a good one to check is the capacitor. Um, so I'm going to stop this video here, but if you want to practice a little bit more, then I think it's a good idea to go through and check some

of the voltages across other components. can start with the capacitor which the leads are right here.

That wraps up this video and I will see you in the next one. Welcome everyone to this video on using our digital multimeter to measure resistances or use it as what is called an ohm meter. So on our multimeter we

are able to measure resistances in the range of all the way from 0 ohms at the 0 to 200 ohms all the way up until this 200 megga ohms. So, we can actually measure a pretty wide range of

resistors. Now, on our board, unfortunately, the resistors, they're just too small to be able to accurately um get in and take a resistance measurement with these probes. They're too big, these hand probes, to actually measure those very small surface components. And I will

show later in the course one way that we can take measurements on these small surface mount components. But, we're going to need uh some different equipment. for this lesson just to demonstrate I do have two bags of resistors here that I will show on how

we can measure. All right, so the first one I've got here is we have a 680 ohm bag of resistors and you see they have one quarter watt rating and they're guaranteed to be within this 5%. So we

can double check and make sure they are actually at 680 ohms or within that 5%.

All righty. So, I'm going to set the multimeter to the 200. They will go up to the 2,00 ohm setting, and that should give us a good reading.

All right. And on these leads, um, you can see there's actually a little ledge in the resistor. Leads just fit nicely into that little ledge. Um, so I'm just going to fit mine in here. All right.

And if I move my hand out of the way, so we can see that this resistor is measuring at 672 ohms. So we are about 8 ohms off of what the baggie is saying, but that's okay cuz we're within that

5%. All right. And I've got another bag here that I'm just going to pop open.

Okay. And this one, actually, I'll just show first. So this one's at 6.2 kiloohms. Again, 1/4 watt and 5% tolerance.

So same thing. I'm just going to put it into the ledge here that is on these leads.

And we can just hold it in place. All right. And you'll notice when I do this one, so on our um so on our multimeter, we are just reading one. And the reason for that is this is a 6.2

koohm resistor and we're just in this up to 2,000 range. So we're over that range. Um, so what I'm going to do is I'm just going to switch it to this 20k range. And then we should be able to

take our measurement. All right. And if we hold it here, just going to make sure I'm holding it tight to get a good reading.

Okay. So, we can see that this one's actually off by quite a bit. Um, so we're at 6 point, you know, hovering around 6.03 kiloohms when it's supposed to be a 6.2 koohm resistor. So, we're still within that 5%, but just wanted to

show how these can vary off by a little bit. Okay. So, if you don't have any of these resistors at home, that's okay. I don't expect you to. Um, but if you do want to make a measurement with your digital

multimeter to check some resistances, then one thing we can do is we can actually measure the resistance between our hands through our body. We were chatting about in the safety lesson how our bodies actually have quite a high

resistance. And I just want to show you how you can make that measurement. So I'm not entirely sure what mine are, but I'm expecting I have dry hands and I do have some calluses on my fingers. So I'm

going to start at the highest reading at 200 megga ohms and if we have to, we can move down from there. Um, so I'm just going to switch mine to this 200 megga ohms.

What I'm going to do is I'm just going to grab the probes pretty tightly here and we'll see what it goes to. All right, so mine is going to this 1.3 and we know that's in mega ohms. So that's

1.3 megga ohms. Um, so that's the resistance through my body right now, which is pretty cool that we can measure it as that 1.3 megga ohms.

I'm just going to lick my fingers here and see how that changes the resistance.

Okay, so I just licked my fingers to get them a little bit wet. And we can see that even already that's bringing um down the resistance value a bit. And if we if I got them even wetter, then we

would be able to bring that resistance down even more. So, kind of cool to see that on our board. Unfortunately, as I mentioned before, it was hard. It is too hard to measure the resistance values with these probes. There is some value

to taking resistance measurements on the board. Sometimes, if we're trying to do reverse engineering and figure out what value resistors are, or if we're trying to match a schematic to a board that doesn't have good markings on it, we can

kind of identify um the areas of the board by looking at the resistance. If you are making resistance measurements on a board and you actually the resistors are big enough you can probe it, it's best practice to take

resistance measurements with the board powered off because that way the current that's running through the circuit will not throw off your resistance measurements. Of course, the way that this guy takes resistance measurements is it actually uses a low voltage itself

and then based on the amount of current that's able to flow, it's able to tell the resistance. So, we don't want to throw that off by having the board have its own current going through it. And also just good safety practice to have

it off. That wraps up this lesson on using the multimeter as an ohm meter or to measure resistance. I'll see you over in the next video.

Welcome everyone. In this video, we're going to be taking a look at another one of the very important features of our multimeter, and that is to take a continuity test. So, if I just bring this up closer to the camera to use the

continuity feature, we actually move this rotary dial to this little symbol right here. And you can see that it's got this marking that looks like it's making a sound. And that's because a lot of people also refer to a continuity

test as beep testing. And we'll see why in just a second. So, I'm going to switch my row. So, I'm going to switch my meter over to the continuity test setting. And we have it here. And what the continuity test means or tests for

is that we have electrical continuity between the two points in this probe. So of course if we are able to just touch these together, we'll see that it starts to give us this nice beeping and that indicates to us that there is a path for

electricity from this probe to this probe, which is something that's very important to be able to test on circuits. Just to give you another idea of what I mean by that, of course, we've got I've got this alligator clip here,

which is essentially just a straight wire. And if I connect it to this red probe, and then as soon as I touch it to this probe, we get the beeping again because electrical signal or an electrical current is able to flow

between these two. Now, this is maybe honestly the most important tool and what I use my multimeter for the most when I'm hardware hacking. And this is because this allows us to be able to tell where signals or currents are flowing on the

boards, especially if we don't have a schematic. We can do what's called beeping it out. So we can, you know, touch from different pins on things like chips to output pins and determine where those are going on the circuit. And we

can also trace through VAS. So you remember when we were looking at the board, we have those VAS that go down to different layers. So if we're trying to figure out, you know, our signal disappears down a via, then we can go

and probe the other VAS and trace where that signal is coming through. So now that we have a little bit of an idea about how this beep testing works, I'm just going to move this to the side, bring the board back, and show a few

areas that we can beep out or start testing on the board. I've got my board upside down here because I do want to make a connection from this ground that we already identified when we were measuring the voltage because one of the first things

that I'm going to beep out or check is see if I can identify any other grounds on the board. And you don't necessarily need one of these alligator clips or this third hand to do this. Um, I could

do it without it, but it's kind of hard to show on the camera or film. So, what I'm going to do is I'm actually going to connect this alligator clip to here. And then I don't have to try and reach under

the board. Uh, and I'll just leave that connected. And I'm just going to flip this board over now.

All right. So, I've got the board flipped over, and again, I have connected this green jack to the underside of the negative pin on this input voltage jack here. And you can do it by just putting the probe underneath

here. It's just kind of a pain to film. So, that's why I have this alligator clip. The other thing that I just want to quickly call out in case you didn't notice is we don't have any power supply

to the board. I have it completely unplugged. And when we're doing these beep tests, we don't want any power. We just want to be checking for the continuity or the electrical signal that comes from our multimeter. So, we'll

leave the board powered off. I'm going to connect the black end to this here so that it's connected to ground. And when I was visually inspecting the board, and this is something that you'll get used to, I did

identify this interesting top piece of bare metal pad here. And you generally won't see these bare metal pads left on a board like this unless they're connected to ground. One of the reasons for that is they just can become an

antenna and add noise or interference. So when I saw this, it stood out to me that I thought that this was ground and I just want to verify that now with the continuity tester. So when we touch to

this, see that I immediately get a beep and that does confirm for us that that is ground. So, what I'm going to leave as a challenge now for everyone. So, if you want to pause the video after this,

is to just go through the board and probe out and see if you can find um any other grounds on the board. There's one that's actually labeled. So, you know that there's an easy one, but there's a couple other grounds on here. So, I'll

just pause it now and see if you can beep out and find some of the grounds.

All right. Did you find any? I'm just going to show a few of them. So I know for example that there is one over here I believe.

Yeah. So we know that we have a ground point over here. And then of course we've got one labeled over here that is a ground as well. And we're going to be coming uh back to these guys later because they are going

to be quite important later on. So, that just goes to show how we can start to test beeping out and checking for continuity. We're going to be using this a bit more throughout the course and helping us to identify where

different pins and different connections travel on the board itself. That wraps up this lesson and I will see you over in the next video.

Welcome everyone. In this video, we're going to be chatting about taking a current measurement with our multimeter or using it in the ammeter setting.

Now, as hardware hackers, it's not as important to be able to take a current measurement. And unfortunately, it is actually pretty difficult to do on a circuit board. And the reason for that is that opposed to how we measured the

voltage in parallel by measuring you know just across the leads or the pins of the component in order to measure current we actually have to insert our meter in series in such a way that all of the current is going to actually

travel through the meter. So we take a look back at our original drawing that we did before where I was showing how to measure the voltage in parallel. I've put a break in that circuit here. And if we wanted to measure current, so we'll

set it to this, I don't know, 200 milliamp reading here. Then we would actually have to put our positive lead here and our negative lead here. And then all of the current, it has nowhere to go. So if I just kind of rest these

down, you think of them connecting to those points. Then all of the current is going to flow into the positive lead.

It's going to go all the way through our meter, back out the black one, and then travel through the circuit, and then back to ground.

So opposite to our input resistance being really really high when we're measuring voltage because we don't want any current to come through and alter the circuit. It is the opposite when we're taking a current measurement. And our input impedance is very very low.

It's generally in the single uh digits of ohms. And the better your meter is actually, the lower that resistance is cuz we don't want to be having any voltage drop over it and affecting the rest of the circuit by putting something

in series. So, this is the reason that I'm chatting about this even though it's not something we're going to be taking any measurements with because this is how it's the easiest to actually damage the meter or blow a fuse. Now, the

reason for that again is the input impedance or input resistance of this is extremely low. So, if we were to close this circuit, so we just draw this closed circuit and we were going to, I don't know, try and

measure the current that's coming straight out of that jack. And we're just curious about it. Um, and we set, you know, this to our 200 milliamps cuz we know that it's we think it's going to be around that. And we were to just then

touch our leads here. So, positive and negative. Then I'll just draw out what's going to happen on this circuit. I already took a measurement and I think in the manual if you read this, it's going to tell you what the input

impedance or the input resistance is. Um, and when I measured it, it was just around 4 ohms. All right. So, I'll just draw out the circuit. We'll say that this is the probe and it's coming down.

Um, and this resistor will signify our actual multimeter in that current reading setting. and it was 4 ohms.

I can tell you right now the impedance of the circuit is going to be much much greater. So what's going to happen is when we get our current flow here, it's almost all of it is going to go

through this top route and it's going to come down our through our meter. Now, if you just do the quick math on this, 9 volts 4 ohms, that is going to give us a current of 2.25 amps, which we already know is much greater

than our meter is fused for. So, we're just going to blow that fuse immediately. And it's really easy to blow these fuses taking the current measurements if we're not doing them properly and we are doing them in parallel. So, I just really wanted to

quickly call that out. Now again, so the reason that this is really challenging to take these measurements on the board is we actually need to break the electrical path or the signal path um that that current is taking. And there's

no really good way for us to do that on a circuit board without actually damaging it. So if we wanted to, for example, interrupt the trace, then we would have to actually, you know, we could take a knife and cut that trace.

Um or we could, you know, cut off the end of a component and lift it up and then try and connect between that. So, there isn't really a good way to take a non-damaging measurement, and that's why we're not going to be taking any.

As hardware hackers, this isn't super important. Um, and just a quick reminder, of course, of Ohms law, and that we can usually calculate the currents as needed quickly mathematically. So, I did want to just really quickly demonstrate, you know,

how you can use the multimeter uh to take a current measurement and just how to do it properly without just using this picture. So, what I'm going to do is I'm going to bring over a quick little very basic circuit and show how

we can actually take a measurement. Okay. So, what I've got here, this is called a breadboard, and it's used for prototyping circuits. Um, so the way that it works is that on these lines that run uh perpendicular to the length

of it, these are all electrically interconnected. Um, so I have the power coming and it travels through this whole top line. And then I have the ground on this battery and it travels through this whole line right here. So what I've done

is I have the LED, the positive end of it comes out to this line here and then the resistor is in another hole. So that means there's a connection here. And then when I tuck this into the ground,

you can see that the LED lights up. So very very basic circuit. Now, if we want to measure the current from this, what we can do is I can again break this connection.

And we're just going to grab a couple alligator clips and I'll show you how we can put this meter in series.

Okay. So, what I've done is I've just broken that connectivity in that circuit and I've connected the alligator clips to each end. So, if I touch these together, we should see this light up.

Yep, perfectly. It lights up. All right. So, if I put the positive end of our ampmeter in through here and then if I connect through here, this means we have it in series. And we're looking at about 11

milliamps flowing through this. So, that's how we take that. Again, we if this were on a circuit board, it would be really hard for us to do this because we would actually have to, you know, either desolder these leads and pull

them out or maybe cut them and then use some sort of jumper. So, there isn't really a good non-destructive way to do it. Before I wrap up this video, just a really quick reminder to be careful when you're taking current measurements. Make

sure you're sure you have it in series because it is the easiest way for us to blow a fuse or damage our equipment. So, that actually wraps up this section and wraps up electrical engineering for hackers 101. So, great job on making it

this far. I will see you over in the next video where we will start over in the electrical engineering for hackers 2011 section and we're going to expand on some of these fundamentals and look more in depth at some of the principles

that we'll need to know for our hardware hacking. Thanks a lot. See you in the next video.

Welcome everyone to the first video of electrical engineering for hackers 2011. In this video we're going to be talking about alternating current and direct current. Now, in the first 101 section of this course, we actually already have been talking about direct current and

all of the circuits and everything that we've been looking at. All the formulas have been in reference to direct current. In this lesson, we're going to be adding in alternating current and talking about the difference that this has between direct current and some of

its important properties. Now, I think using current to describe these is a little bit confusing. And the reason for that is when we're getting power from a power supply, the voltage being supplied is set by that supply and

then the current is actually proportional to that voltage. And we know that the current is going to be proportional to the voltage and the resistance in the circuit. So I think it's a little bit easier to think of

this as direct current actually meaning a fixed voltage and then alternating current. What that means is that we actually have a fluctuating voltage. And just to give a little bit of a representation of what I mean by that,

we're going to go back to this very first image or pictographic representation of a circuit where we have this voltage and the voltage creates a current that goes through our circuit and through our light bulb. And if we look at this as a direct current,

so in our example, that would be a fixed voltage. One way to actually represent this voltage that will make more sense with these alternating current is in a graph. And on this graph, we would have voltage being the yaxis. So how much

voltage we have and then on our x-axis is over time. Now with a fixed voltage or a direct current, we can see that this just makes a horizontal line. So in this example, the voltage stays the same. It's just a fixed voltage. And as

we go through time, that voltage level is the same. Now we know due to Ohm's law that the current is actually going to be proportional to that voltage and it's also going to be a fixed level.

Of course the value that this current is going to be is proportional to this resistance. However, we know that it's going to be set unless the resistance change is going to be the same current level. If we change this though for an

alternating current. So we'll say that this is an alternating current. And I'm just going to bring up a marker here to draw on the graph what that might look like. So one example of alternating current that everyone is probably

familiar with is the voltage that comes to our house. And the way that this voltage changes over time can be represented with a sine wave. So the voltage comes up to its peak voltage and then it comes down to here. And of

course, if we represented the current at this point, it would come up to here and come down. And of course, this current again is going to be proportional to this resistance. But we know that as far as the graphs go, they're going to

follow the same shape. Now, what happens when we get to this point on this? So, once we actually start, you know, going the voltage into the negative, then the current is actually going to go into the negative. And we see at that point that

our voltage actually flips and then the direction of our current changes. So this is kind of where that alternating current terminology comes in because our current is now flowing the opposite direction. So of course if we finish this drawing,

it's going to look something like this. And our current is going to follow And in the sections where our voltage flips into this negative, of course, our polarity is going to swap here and our current is going to start actually

flowing in the opposite direction. So, one example of alternating current that everyone is probably familiar with is the power that comes into our house.

Now, in North America, this operates at 120 volts AC at 60 Hz. And we'll talk about what that means a little bit later in this lesson. Now, you may be wondering why I'm talking about alternating current if we actually are

not supposed to be touching anything with our household power or the power from our sockets in our house. And that is absolutely correct. Again, shouldn't be working on that. However, we do use this alternating current or fluctuating voltage for a lot of other very

important things in electronics. So, just to represent that, I'll show this graph here that represents a fluctuating voltage over time. So this waveform here that we have where it goes from this 0 to 5 volts is a good representation of

something we could see in an IoT device. Many sensors are very good at changing the voltage that they supply based on how they read something. An example of this could be a temperature sensor where as the temperature changes the voltage

that is output by that sensor would change. So we could see a change in a fluctuating value like this. So, I just want to bring up a second wave here that's going to help bring this point home for why these alternating currents

are important in our IoT devices and electronics. All right, so I brought up a square wave here and these are very important for how we do digital communications where we will have a high voltage represent a one and a lower

voltage represent a zero. And even though these are more what we call a square wave, they are still a type of alternating current. And as such they behave differently than if we just have a fixed voltage. So that is why it's

really important for us to learn a little bit of the fundamentals about how alternating current functions and changes things in our circuit. I'm going to go back to just a plain standard sine wave here so we can talk about some of

the important ways that we actually describe and measure alternating current. The very first one is what is called amplitude. So the amplitude is the distance between um the zero or the midle if it is going from positive to

negative to the top of the wave. So this would be the amplitude for this sine wave. The second one we'll talk about is the peak voltage. So this is the um highest voltage that's represented and it's actually the same as the amplitude

but sometimes you will hear it um called the peak voltage. So generally when we have a sine wave that is not fixed amplitude like the one we saw in the last the peak voltage will be the highest one. So the highest that it can

get. All right. The next one that we'll talk about is the peakto peak voltage which is VPP and that is the measurement of the top peak to the bottom peak. So it will be um double the amplitude.

The next measurement or calculation here that I'm going to show is not actually important for this course, but I just really wanted to show it out of curiosity. In case you're wondering, for example, at our household voltage, that's 120 volts AC. Um, which voltage

is that? Is that this peak voltage or this peakto peak voltage? Well, the answer is that it's actually neither of those. That 120 volts AC is actually what we call the root mean square voltage or RMS. And I'm going to quickly

show here how to do the RMS voltage calculation for a sine wave. Now, there is a bit of math behind this that I'm not going to show cuz it's outside of the scope of this course. So, just keep

in mind this is for a sine wave like we use in the North American household voltages. So to calculate RMS it is equal to the peak voltage divided by the square<unk> of 2. And we can actually approximate the square<unk> of 2 as

1.41. So the peak voltage for North America is actually 170 volt if you were to measure this actual top peak voltage.

And of course if we do 170 divided by 1.41 and this gives us just around 120 volt AC.

Now the reason we use this RMS voltage is because if you were to compare its equivalency in DC. So if we think back to our circuit where we have our light bulb uh and if we want to kind of think

about the brightness of the light bulb or the actual power delivered to that circuit the equivalent AC to DC would be the RMS voltage. So if you have 120 volts DC um then you want to compare this to AC then it would be equivalent

to that RMS voltage. So that's why we use um this RMS when we're talking about it. And if you ever see, you know, voltage for our household at 120 volts AC, you can know that that's actually in this RMS calculation. Again, we don't

need to know this for the course. I just thought some people might be curious about that. Okay, so I've brought up a square wave cuz there are a couple specific things we should talk about with regards to square wave. Now, the

frequency and period and amplitude that we talked about in sine waves, those are all going to be the same for square waves. However, since we do have this wave changed a little bit and how it's formed, there are some different

characteristics that we use to describe it. Now, the first one is the pulse width and this describes just how long um this like if we think of this as the on portion of the square wave where we're actually applying a voltage, the

pulse width is how long that pulse goes on for. So we see in this example of this first portion of the square wave, the pulse width is 0.1 seconds. And in this first section of the square wave, we have uniform between how long it's

off. So it's off for 0.1 seconds and on for 0.1 seconds. Um, and this whole section right here would be one period.

And then we would know that the frequency for this would actually be 1 over 0.2 two because our period is 02 seconds. So we would have a five Hz frequency.

Now what happens if we don't have this uniform square wave? So I'll just bring it up here. What happens if we actually um have like a longer resting period than we actually have our on period. Now the way that we describe this is with

what's called the duty cycle. And the duty cycle explains the ratio of the pulse width or the on duration to the actual resting period in that period. So it is a proportion. In our first example where we have this pulse width that is

equal to this resting period then we have a duty cycle of 50%. So the duty cycle which is represented generally with a uppercase D is calculated by the pulse width over the period duration. So for example in this one we have 0.1. So

the pulse width is 0.1 seconds divided by this whole period which is 0.2 2 seconds, which gives us 50%.

In most of the waves that we're going to be looking at for digital communications, we're just going to be working with a duty cycle of 50% and we're going to have that fixed pulse width. However, I just wanted to show

these terminologies because you may hear them come up and they're important to how we describe these square waves. That wraps up this lesson. I'll see you over in the next one. Welcome everyone. In this video, we're going to be taking a

look at capacitors and talking a little bit more about them. Now, we have already chatted a bit about capacitors in the safety lesson and then also when we opened up a router for the first time and we're looking at the PCB, there were

many capacitors that we would have seen on that board. And we haven't chatted about them fully in depth yet because we needed to have an understanding of alternating currents before all of their functions make sense. So now that we

understand about alternating currents, let's take a look at cow capacitors function. Okay. So I've got up on the screen here the actual schematic representation of a capacitor. And you'll notice that it is two what we see as like conductors or almost wires that

are parallel to each other. And we just have some air in between it. So it kind of almost looks like an open circuit.

And then we've got our leads connected to it. And the reason for that is this actually mimics the construction of an actual capacitor. So if we take a look here at a cross-section of a certain type of capacitor, which we call a

ceramic disc capacitor or just a ceramic capacitor, you'll notice that on the inside we have what's called the electrode. And it's just a large metal plate with a big surface area. See, we tried to make it as thin as possible and

make the surface area as big as we can. And this is connected to the actual leads here. And if we looked on the other side coming to this lead, there would be an identical plate to this one.

And then it's actually uh sandwiched in between we have this ceramic disc. And the ceramic material is what we call a dialectric. And what this means is that it is does not actually conduct any electricity. So, it doesn't allow any

electrons to flow through it, but it's very good at holding these electric charges on the outside of its material.

And this is super important for how the capacitor functions. To better understand and see this in action, let's take a look at it in a circuit. I've got a very basic DC circuit here with just a 9V DC power

supply and a switch that's closed and a capacitor in series with that. So what's going to happen in this circuit when we throw this switch closed is that we will initially get some current that travels through and in this DC circuit what's

going to happen with those electrons is they're actually going to pile up on those electrodes or plates. And because we have this dialectric in between here, they're not actually going to be able to flow through to this wire. So we will

get an imbalance of those charges piled up on these plates here. And when we get that steady state and the capacitor is what we call the charge state, then we'll get the matching voltage across this. So if we were to measure the

voltage over this capacitor, we know of course because of Kaw's voltage law, it's actually going to be that 9 volts.

And at that steady state, we'll actually get no current through here. Now, of course, in a real life scenario, we wouldn't just hook a capacitor up like this because it really has no function.

It's basically just creating an open circuit for us. So to give a better representation of what they're actually used for, let's take a look at a more real life applicable scenario.

So I've added into our circuit here this 350 ohm resistor and an LED that we're going to be lighting up. And let's say in this circuit um the switch is open and it has been open for a very long

time. So there's actually no charge left in this capacitor. So if we were to measure the voltage here, it would be 0 volts. we have 0 volts over this capacitor and our light would be off.

When we throw this switch closed, let's see what happens when we throw this switch closed. We're actually going to start to get some current coming through um and it won't actually go through this capacitor. But what's going to happen is

over time the capacitor is going to charge up and it's actually going to happen fairly quickly. This is going to be um you know almost instantaneous but as it charges we will get some current and the current is not actually

traveling through the capacitor. What's going to happen though is we're just going to induce a current because we're going to have um you know if we look at it at this time for example right here then we don't have a fully 9 volt charge

here. We're going to have an imbalance of that voltage and that's going to induce some current. However, once we actually reach this steady state here and we get to that 9 volts, we're not going to have any current here. And our

circuit's just going to function as it would normally with that series circuit of our resistance and our LED. Our LED will be lighting up and we will be all happy because that's what our circuit is designed to do. Okay. So what happens

though if we throw open this switch and we do that to simulate maybe we have um a little dip in our voltage supply or the the power cuts for a second. What would happen in that scenario?

All right. So immediately what's going to happen then is we have this 9 volts here and it actually will function kind of similar to a battery. So we'll see here we actually start having our current being induced because we can

think of the polarity of this. So we have a minus and a plus here and we can treat it kind of like a battery and it's actually going to power our LED and our circuit for a brief period of time. So

if we take a look again at the graph for that, it's going to look something similar to this. Now this dotted line here represents when we throw open the switch. So in our steady state, um the voltage here is just happy at 9 volts

and we're going along in that straight DC. And then when we flip open the switch, what's going to happen is our capacitor is then going to kick in and it's going to discharge very quickly. Um all of its charge and it will actually

be able to power the circuit for a brief period of time. See here that it actually dips pretty quickly and it follows this um then slowly discharging.

So, while this isn't a perfect power source for us or voltage source because of course our voltage actually um drops in time pretty quickly and with it so does the current that actually comes through the circuit. It will actually

help us with some quick dips in our voltage source. So maybe if we only came to here and then we came back on, we'll come right back up to that 9 volts quickly. And that's a lot better than us

just dropping off this peak. So this is why you'll generally see um these bigger size capacitors in the power supply because they really help to even out if we have any dips or drops in the voltage. Then they can keep our circuit

running as it should for a brief period of time until that voltage kicks back in, which is a really nice feature. Now the amount of charge that we actually hold is what's going to determine how quickly this capacitor discharges and

how long we can actually supply some voltage and current. And the property of a capacitor to actually hold onto this charge is what's called capacitance. So you'll see here it's capacitance and we usually denote that with the letter C

and it's measured in the unit farads. Now one thing to note with farads is this is actually a very large unit and an electronic circuit. So things like our IoT devices, we're generally going to be seeing things in the range of

microfarads or sometimes even nanoparads or poparads. So those are just very small fractions of the um SI unit which is farads. So this demonstrates how capacitors behave in a DC circuit. And the one really important takeaway for this is that in its steady state,

there's not going to actually be any current that is able to flow um through the capacitor if it's hooked up to a voltage source. So keep that in mind.

You can think of it at DC in its steady state that it's basically an infinite amount of resistance. This is not the case however though for alternating circuits. So we're going to take a look at that now. Okay. So I've just brought

up a very basic circuit here where I am showing what we have an alternating current voltage source. So this little squiggly line inside of the circle. This is what we actually use in our schematics to represent an alternating

current voltage source. And just for ease of calculation and what we're used to, I'm using our North American um voltage here. So 120 volts at 60 Hz.

Now, as I just mentioned, if this were a direct current voltage source, then what's going to happen in our steady state is the current's going to come.

We're going to build up those charges here, and then once we reach that steady voltage that matches our voltage source, then nothing's really going to happen in this circuit, we can kind of just think of this as being an open circuit, and we

will have no current coming across our resistive load here. For an alternating current, this is actually not the case.

the alternating current is actually able to interact with this capacitor and transfer its charges over through to it which is actually going to then um create a current on this side here. Now one thing that is important to note is

that we're not actually still passing electrons through this. This dialectric doesn't allow them. But the alternating voltage here that comes with our alternating current is actually going to um cause this charge to build up and then discharge. And that imbalance of

charges is going to allow us to transfer the current over to this side and we'll actually have some current through. Now, capacitors still do resist the flow of an alternating current. And the amount that they resist that flow of

alternating current is what we call reactants. And the calculation for reactants here, we are going to start to get into um a little bit more math. But the calculation for that is it's 1 / 2 pi.

And this f is frequency. this little f not farads and then c for capacitance.

Um so the most important takeaway here just to remember is that it is inversely proportional to the frequency and the size of the capacitor. So as we increase this frequency the higher it is then the less that this capacitor is going to

resist that alternating current and also the greater the size of the capacitor then the less it's going to actually resist this flow of current. So if we were to calculate it for this capacitor, of course we're 1 / 2 pi fc. So if we

plug in our numbers, we have 60 hertz and then this is 100 microfarads if we just convert it to farads and we're going to get 26.5 ohms. Now one important thing here is we can't actually just add this reactance with a

resistive with a purely resistive resistance. And unfortunately the math does start to get a little bit complex here about how this works and it requires some trigonometry and I'm just not going to go into that in this course. If you are curious about it then

I would encourage you to take a look more and study more in depth about it.

But I'm just going to show some of the formulas here for it and how it works and I'll tell you about the key takeaway. So we want to combine our purely resistive resistance with this reactance. What that's called is and you

probably heard me mention this a few times uh is called impedance. And we denote impedance with this zed here.

So for a series RC circuit, and this math only works for a series RC circuit, which is what we're mainly going to be working on. And this RC circuit means we just have a resistor and capacitor in series. We can calculate the impedance

as the square root of R2 + X^2. So this is our resistance here. And then this is our reactance.

So for our circuit that's going to be 350 squared, which is this measurement of the resistor. And then we already calculated the reactance as 26. So we'll do this 26^ squ. Um, and I'm just making dropping off that.5 here just to make

this calculation super simple. And we get this 351 ohm. So the big takeaway here and what I wanted to show is that this 100 microfarad capacitor is really only adding about 1 ohm of impedance to the current. So it's

really having very very little effect on how much current is actually flowing through the circuit. And if we increase this frequency or we increase this capacitance value then it's going to have even less effect on it. However, if

we decrease this frequency, so as we get closer and closer and closer down to our DC, which would be, you know, zero hertz, we're going to get more and more and more impedance till we basically reach what is considered an open circuit

or impedance so high that we're not going to allow any current to travel through the circuit. And this is the most important takeaway for this. So if you don't remember any of the math or what impedance or anything like that is

just to remember that capacitors at a higher frequency are going to offer very little resistance. And the higher the capacitor value we go is also going to offer very little resistance. Now this is super important for when we're

working on our IoT devices or really any circuit that's going to be working with alternating currents because what it allows us to do is we can create what are called filters. And what we can do with these filters is that we can

actually then block certain frequencies from going through to our circuit. And this is going to be really important for when we're working with all these communication signals and we have our square waves with different frequencies and we have interference. We're going to

need these capacitors to create these filters. And that's why if you recall when you're looking at the board for the router, it was filled with capacitors because this is trying to create a wireless signal. So, we're going to have

lots of different frequencies going all over on that board. And the capacitors are what actually allow us to filter out and keep only the ones we want. In the next video, we'll actually take a look at how we can create some of these

filters and simulate them in Circuit Lab. But before we hop over to that, I just want to loop back to our original look at the three capacitors we started this lesson with and just chat a little bit about some of their properties. So,

on the left here, we have what's called an electrolytic capacitor. And the reason it's called that is because if you were to bust this apart and take a look at the inside of it, instead of just having two simple plates, we

actually have a sheet, a very thin sheet of metal conductor here. And it's rolled around in a circuit like almost if you think of like one of those like Swiss logs or something like that, those baked goods. It kind of is similar to that.

And then on the inside where between what is rolled, instead of ceramic for a dialectric, we actually have um an electrolytic compound. like a gel and it's a very very good dialectric. It's better than ceramic and what that allows

us to do is we actually can make these capacitors much much bigger in capacitance. So if we need a um bigger capacitor or bigger capacitance then we have to use these electrolytic capacitors. Now the one really important thing with these is they actually care

about polarity. So which one gets hooked up to the negative and positive ends. Um, and the way that we can see that is this will usually almost have a piece of like marking tape or indicator that's the negative one. And then also the lead

on the negative one will be shorter and the positive lead will be longer. And this is true for a lot of components that have polarity. The the longer lead will be the positive one. And one way that I was taught to think about this

just to help you if you're ever going to forget that. So, if you think of like a positive symbol and you take like two lines for example and you cross them like this, well, if you uncross those, put them together like as a lead, then

it's going to be longer than if you just took a negative and put it as the lead.

So, that's how I always remember that the longer one is the positive one. All right, so the next one that we're going to take a look at is what we've already taken a peek at actually, and that is

the ceramic capacitor. So, we saw what was on the inside of this one. And these are great if we just need a fairly low capacitance because they are very cheap to make. And also, the other nice thing is we don't care about the polarity on

them. The last one here is a surface mount capacitor. So, we can make them in that surface mount package. And you'll see lots of those on our router board, for example. And this is actually a ceramic surface mount capacitor. So,

it's just got a piece of ceramic uh in between two little metal tiny metal plates here. All right. So, the last very important thing about these capacitors is you'll see on them they have two different markings. So, the

first one just tells us about the capacitance. On this one, it's 100 poparads. And then we'll see this 1,000 volts for example on this one. And this one's rated at 6.3 volts. So this voltage is kind of similar to when we

had the current for our power supply in that this is not actually the voltage that they operate at or anything like that. This is the maximum voltage they can withstand. So the voltage that the capacitor will be charged at is whatever

voltage we apply to it. But if we go over a certain voltage that is more than it's rated for then like these guys will actually blow up. You'll see them they'll go pop and they'll blow up. Um and these ones will just burn out. So,

we got to keep in mind to take a look at that voltage rating. That wraps up this lesson on capacitors.

I'll see you over in the next one where we're taking a look at circuit lab.

Welcome everyone. In this video, we're going to be picking up from the last lesson where we were chatting about capacitors and we're going to be doing a quick demo in Circuit Lab to show how we can use just capacitors and resistors to

create both a highpass and lowass filter. So, if you're following along or you want to follow along in your browser, you can get to Circuit Lab from www.circetlab.com.

And at the time of recording this, you don't need to create an account or log in. You can use it for free. However, you are limited to a set amount of time per day. So, just keep that in mind. Um,

I have created an account and purchase their membership. I think the one that I have is about $20 a year. Just wanted to be able to support them and also have that unlimited access. So, if you are enjoying their uh website, consider

buying that membership. However, you should have enough time and be able to follow along with everything that I'm doing uh with the free version without logging in. So, what I'm going to do is I'm actually just going to dig in here

and create um a common scenario that we have and what we could use a filter for.

So, I'm going to add in an alternating current uh voltage source here. So, that's this symbol here if you remember correctly. And I'm gonna make it um one volt amplitude, but I'm gonna make it 60 Hz. So, it's kind of like the voltage

that's coming from our house. And then I'm actually going to add in a DC voltage source here.

And I'm going to make this 9 volts, similar to the voltage source that we are using. And then what I'm going to do is I'm just going to add in a single resistor.

We'll just do a 1k resistor. Add in some grounds here. Going to connect these up with the wire.

Then I'm going to add these nodes here. So we'll call this one the voltage in.

And we'll say this is what we're measuring our voltage out over. All right. And for those of you following along at home, you will notice that in this scenario, I mean, these are the same nodes. So, of course, the voltages and

everything's going to be the same, but you'll see later why I have added those.

Now, if we use what we previously did to check the currents and voltages here, we can actually see um our 9 volts DC here and we actually have this 9 milliamps.

However, this is just purely the DC portion of the circuit. So, the part that comes from here. Um however this little bit of sign noise that we have here is actually going to um affect the circuit. In order to see how that

affects a circuit, we need to take a look at running a simulation for this because of course this voltage source it's going to alter over time and we want to take a look at how that plays out over time. So what we can do is run

a simulation. So, I'm going to click down here, simulate, and we're going to do a time domain simulation because what this is going to allow us to do is it's going to let us plot the voltages and the currents in graphs over time. That's

kind of similar to how I've been showing them in the whiteboard lessons that we've been doing. Going to set the start time at 0 seconds. That's just when the plotting is going to start. And I think 100 milliseconds is an okay duration to

run this. We'll be able to see enough periods of our wave in that. Um, and then this last one is the time step. So that's how frequently we are plotting the graph. So I'm just going to do 10

microsconds. That's going to give us lots of plots on the graph so that we can see uh nice smooth waveforms.

And then it's going to ask here for us to add expressions. And this is why I've added these V in and V out.

And we can just run a time domain simulation now. And we'll actually see that we have this V out which is the orange one. And then the V in if we just actually hide the V out one. See the V

in is the same as the V out which we were expecting. However, we'll see here we wanted a purely 9V DC signal. I mean if that was our goal and we have this one amplitude um of noise at 60 Hz. And

in actual circuit designs, if I just hide this, this is something that can happen with poor quality power supplies or if the power supply um itself doesn't take care of this with this 120 volt 60 Hz that comes from our wall. If we're

plugging, you know, our power supply into the wall and then it's supposed to transform this to DC and step it down to 9 volts. Sometimes what can happen is this signal is so strong that electromagnetically um we can still get interference and we

can get some of that signal into our power supply. Um or especially if we have like an antenna where we're trying to pick up a wireless signal or something like that. Um we can get a little bit of this 60 Hz signal um

induced onto our line and that's what I'm simulating here by doing that. So that's why we have that, you know, 1vt is actually a quite a bit of noise on top of our 9volt power supply. So what I

want to show here is how we can quickly start to get rid of that. So, if we actually I'm what I'm going to do is I'm going to go back to build here and I'm going to grab this resistor. Um, and

instead of putting it and instead of measuring the voltage out over the resistor, what I'm going to do is I'm just going to drop it in here.

And I'm going to grab a capacitor and drop this capacitor down into ground. I'm going to set this capacitor. We'll start with 10 microfarads.

I'm just going to rerun the simulation with these same parameters. All right. So, we can now see that our via out is actually um changing and we're getting closer to, you know, squashing it down to that pure 9V DC

signal that we want. Um but we still do have a little bit of jitter. We've cut it down to I don't know about here 9.37.

So, we've cut it down about 60%. But, we still can do better than this as far as just getting a straight line. So I'm going to hide this and then we can go back to the build.

So the way that I like to think about this or how this filter works is that we have this resistive load here of 1 kiloohm and then we've got our 10 microfarad capacitor and we know to our 60 Hz sine wave these higher frequencies

that um the impedance or like what we can think of as the resistance of this capacitor is very low. And so essentially what we're doing is we're just allowing the sign portion or the the alternating current portion to pass

over this with very little impedance. So what that means is that it's actually going to drop most of its voltage over this resistor because the impedance is much greater. And then for this 9V DC signal, of course, it can't even

actually travel over this because it sees this as an open circuit. Now if we want to improve our filter and get it closer to being that flat line, we have two options. So, we can either increase the resistance um or we can increase the

capacitance. So, I'm going to increase the capacitance here. Let's just do it another 10 times and bump this up to our 100 microfarads.

I'm just going to run the simulation again. And we can see now we're getting pretty close to that nice smoothed out straight line. We do still have a very bit of noise in here. We're looking at like 0.05 volts of noise. and our circuit's

probably going to be able to um handle that if it's looking for a DC at 9 volts. Uh but we can do better. So, let's just hide this and let's pump up our resistance again just to see how

that affects it. Um so, let's just double this guy to 2 koohm resistor and we'll run the simulation again.

You can see we're getting even closer and closer to what would be a straight line.

Now, of course, we can do the opposite here. So, I'm going to do is just click build here. And we can reverse these.

So, grab this. So, I'll just delete that. Grab this. Rotate it. And just fix up my circuit here.

Drop this in. 2k. So this circuit it the so the other circuit is what was called low pass filter in that we only were letting those low frequency or in our case just the DC frequency to go by. Um and now if

we reverse this then this is what's called a highp pass filter because we're only going to be allowing those high frequencies that we want to go by. Um this one is actually maybe even a little bit easier to visualize because of

course basically just creating um an open circuit here. So none of this DC voltage is going to be able to pass here to where we're reading this out. So if we just simulate this and we run our time domain simulation, we can see that

our Vout is basically just this one volt and we don't have any of this 9 volts that would have brought it up here and that 9volt DC interfering with it. So we've got a almost perfect filter here where we are bringing it down just to

the original alternating current sine wave. So hopefully this little demonstration just gives a little bit more details about capacitors and how we can use them as filters. Um we can start to get a lot more complex with what we do with the

capacitors and our filtering to make what are called band pass filters where we're only going to allow a specific frequency band. So instead of it just being anything over or under a set frequency, we can actually also create

them. So if we just want a set frequency range, so maybe from like 60 Hz to 120 Hz. So, what I will end on with capacitors is I've really just barely scratched the surface um of the theory that's behind capacitors and how they

affect signals. There's a lot more if we want to start talking about phase and leading and lagging currents and voltages, but I don't really think all that stuff is super important for us as hardware hackers. The main thing I

wanted to impass is just what they're usually used for in the circuits that we're going to be looking at and how they can play a role as filters. So, that wraps up this video here and I'll see you over in the next one. Welcome

everyone. In this video, we're going to be chatting about inductors. Now, when I was putting together the curriculum for this course, I wasn't entirely sure if I was going to include a video on inductors or not. And the reason for

that is they won't be as frequently seen in small electronics that we're likely to see in IoT devices. However, for both completeness and because some of the science behind why inductors work is important, I've left this video lesson

in. So, with that being said, let's dive into taking a look at inductors. I've got one on the screen here, and then I've also got the schematic symbol here.

Now before we chat about conductors, we need to look at another important electrical engineering law. And that law is Ampier's law. And what Ampiier's law says in like the most basic form is that when we pass current through a

conductor, so we look again at our very basic simple wire and we'll imagine that this one is actually connected to a voltage source. So that's how we're able to pass a current through it. And when we pass this current through the wire,

it's actually going to create a magnetic field around that wire. And I've got these blue rings here on the screen that represent the magnetic field. But just keep in mind this is a field. So it exists all around the wire. And as we

get further away from the wire, the magnetic field exists, but it weakens in strength. Now the direction or what we call polarity of that magnetic field is actually proportional to the direction of the current. So if we swap the

direction of the current, you'll notice here that the polarity or direction of that magnetic field reverses. So Ampear's law is super important actually for how we interact with and use electricity in our day-to-day lives. And one of the reasons for that is that the

opposite actually also holds true. And that is that magnetic fields actually are also able to induce currents. So you see here I have that same wire from before and I've just shown these rings kind of expanding out to demonstrate how

that field would propagate outwards. So keep in mind that as we get further and further away from the wire that the magnetic field is actually going to weaken in a strength. Now, if we put another wire inside of this magnetic

field, what's going to happen is that it's actually able to induce a current onto that wire, which is really, really important actually for a lot of our daily uses of electricity. So, this is kind of one of the fundamentals of how

we generate electricity. It's also how electric motors work and it's also how we transmit a lot of our wireless signals throughout the air.

Now the one really important thing to keep in note with how this magnetic field induces currents is that it's not just a magnetic field that induces the current. It's actually a change in magnetic field.

So when we first put this wire inside of that magnetic field, we're going to induce current for a short period of time. But then we kind once we reach that steady state and if neither of these wires are moving and this current

is not changing then we're going to lose this current that we're inducing because it's only the changing magnetic field.

So in order to induce a current if that's what we want we have a couple of options. First of course we can move this wire. So we can move it in and out of the magnetic field. And remembering

that the magnetic field changes in its strength as we get further from the wire. So this change is going to induce a current. Second is of course we can move this wire so that it makes this further. And then the last thing that is

really important is we can also use an alternating current. So if we flow an alternating current through this wire that's creating the magnetic field. Of course as we change that current, this magnetic field is going to change in its

intensity and also possibly its polarity if we have this current going back and forth. And what that's going to do is it's going to induce a current onto this other wire. So something super important to keep in mind.

With that in mind and a little bit of an understanding of Ampi's law, let's take a look at how we can use this to create inductors.

So I've got an example of an inductor here on the screen. And really in its most basic configuration or construction, an inductor is just a wire that is coiled up. So you see here in this illustration we have a wire and

it's coiled around itself many times and you know in this example it's not many coils um just kind of pictoraphically but in reality we're going to have you know up to thousands and thousands of times that this wire coils around

itself. And when we do this, these magnetic fields are going to form in such a way that they create uh a magnetic field in this kind of pattern where it's the strongest in the center. And what we can

do with this kind of magnetic field like this is we can actually store energy in it. So when we send a current through the inductor and it travels all the way through it even if it's just a DC

current when it travels through and it's you know at that instant of it changing it's going to create that magnetic field and then if we actually remove that current and as long as you know we still have a path for current to flow then the

magnetic field is actually going to recede and it's going to release all of its energy back into the wire. So, in the same way that capacitors were able to store their energy in that electric field, inductors are able to store their

energy in this magnetic field that can then be released to create current back into the wire. Another thing to keep in mind is that this magnetic field as it's being created or changing actually creates a resistance or impedance on the

current. So when we apply just a direct current to this wire at the very beginning when it's first being applied as this magnetic field is being created it's going to create some impedance for that current but then once it reaches

that steady state the magnetic field uh and the current are stable then it's not really going to apply much impedance at all. We can just think of it to that direct current or a very low frequency as almost just being a straight wire.

However, for an alternating current and especially one that is fluctuating at a very high frequency, then the change in current is going to constantly be trying to um change or fight against this magnetic field. And what that's going to

do is it's actually going to create quite a bit of impedance for that alternating current. So, we'll take a look at the next slide about how that impedance and reactance is calculated.

Okay, so I've got a very very basic circuit here. Again, similar to the capacitor and resistance circuit that we are looking at. Now, you'll notice that I have swapped out our voltage source here with a 10 kHz frequency. And that's

because inductors, they generally interact much more with these higher frequencies and impede the higher frequency. So, I have upped it to make it a little bit more realistic in the actual value of the inductor. So, similar to capacitors, inductors do have

a measurement for how much energy they can store. And we call this inductance. It's usually measured or denoted with an L. And the unit for it is Henry's.

Similar to capacitors, Henry is a pretty large unit. So, you're generally not going to see inductors having a measurement of a full Henry. A lot of times, you'll see it in millhenries or maybe even micro Henry's.

And again like capacitors the amount of resistance that they have to alternating currents is called the reactance. We generally denote this with an XL. And the calculation for it is 2 pi * the frequency times the value of the

inductor. So the amount of pen's and you'll notice that kind of opposite to capacitors our reactance is directly proportional to the frequency and the size of the inductor. So, as we increase the frequency or as we increase the

inductor, then we're going to get more reactants. In our example here, we can see if we just run the quick math, we're going to get around 6,283 ohms of reactance. And if we convert that into impedance following the

similar method that we did for capacitors, I won't go over all of the math again, but if we just really quickly run through this math, you'll see that we're going to be getting an impedance around 6,292 ohms. So adding this inductor in series

for this um somewhat high frequency is going to add a lot of impedance. And this honestly, this really isn't even that high of a frequency. So, you know, we can get up into the megahertz or gigahertz in signals. So, you can see

how um at these higher frequencies, these inductors are actually going to start to be almost like uh an open circuit or infinite impedance for these really high frequencies. Just to really quickly circle back to my initial comment from the start of the lesson on

how we won't see inductors as much in smaller electronics like we're going to see in IoT devices. Now the reason for that is twofold. The first is that inductors themselves are costly to make in comparison to capacitors. So if we

look at this example here, we've got an inductor um or even this one on the circuit board here, you can see how we actually have to take a wire and then either wrap it around itself or wrap it

around some other material. And this manufacturing process for this is more expensive. It just costs more to actually do this than a capacitor where we can just take two metal plates and slap them together over top of a ceramic

disc or some other material. It's a lot easier to make those capacitors. The other reason is if you look at this circuit board, this is kind of an old school circuit board, but just to really demonstrate it, I've got an inductor

here and then we've got some capacitors here. Now, these are much smaller um like in their ability to store energy.

And you do see we've got some big capacitors here, but overall inductors are going to be a lot bigger than capacitors and take up more space on the circuit board. And then also, we still have that u magnetic field that we have

to worry about that inductors create and they can actually be a source of noise on our circuit boards for us. So, if we're not careful about where we put them or if we're shielding them properly, then that magnetic field that

they create, it can actually bleed out into the rest of the lines on the circuit and it can be a source of noise for us. Now, we did see just in our previous example how inductors could be an excellent filter, especially for

these high frequency signals and blocking them. But keep in mind that we can actually use a capacitor to block high frequency signals as well. And we demonstrated that in the capacitors lesson where we were able to create what

we called a lowass filter that just let the low frequencies through and block those high frequencies. And then using that same capacitor and resistor and just switching the order of them in the circuit, we were able to do the

opposite. So for a lot of applications where we would use an inductor, we can actually use a capacitor instead. And since they're cheaper, smaller, and easier to produce, we just select to use a capacitor. Now, there are some

specific cases where inductors are better, and I'm not going to go into those, but you will sometimes see them on the board. So, it's something to keep in mind. That being said, inductors also play a really important role in lots of

other areas of electrical engineering. So if this is a topic that you are interested or you want to learn more about them, I've honestly have really just scratched the surface about both inductors and how Ampier's law functions. So definitely would encourage

you to dive deeper into that. With that being said, that does wrap up our video on inductors and I'll see you over in the next one.

Welcome everyone. In this lesson, we're going to be chatting about diodes. So, I've got the schematic symbol for a diode up here and then a picture of a very standard through hole style diode here. Now, they do come in many other

packages, but this is what the common through hole ones are going to look like. This is another circuit component where it really makes the most sense to take a look at it in an actual circuit.

So, let's take a look at a basic schematic that has a diode in it. And we're just going to revisit that really basic DC circuit that we were looking at before where we have our 9volt DC power supply and we've just got a resistor

here and we've dropped a diode in series with it. So just for the explanation of how this diode functions, I'm going to drop in two circuit nodes here and just to help label the polarity of the diode.

So this end of the diode is the positive one and this one is the negative one here. And you regularly won't see dodes represented like this in schematics. I'm just adding this here because it makes it a little bit easier to understand

what's going on. If we just bring that picture of the diode back just so you can see. Um, this end is the positive end. So it correlates to this end here.

And this end is the negative end, the one with the stripe on it. Or the way that I like to think about it is that this is just a negative symbol. And the positive end of a diode is called an

anode. and the negative end is called a cathode. It's not super important to remember those, but just so you know, that's how they work. The way that I remember it is since anode comes in, you know, alphabetically before a cathode,

it's the positive one. And the way that diodes function and why we needed to talk about this polarity is they they actually work similar to uh like a valve in water in that they control the flow. In our case, it'll be

the flow of electricity, so current, in such a way that they're going to allow it to only flow in one direction.

So if we hook this diode up in such a way like we have here where we have the positive end or the positive lead hooked up to the positive end of our voltage supply and then we also have the

negative end hooked up to the negative or to ground then this is going to allow current to flow as it would here and it's going to offer very very little resistance to this current.

If we flip this voltage supply around so you see here now I have flipped this.

So, you know, we've got this negative to positive, and we're going to actually have our current be trying to flow this direction around our circuit. And of course, we've got the negative end of the diode or the cathode hooked up to

the positive end of the voltage supply. And this is actually going to block any current from flowing. It's going to basically be like an open circuit. We do have a very, very small amount of current. That's called the leakage

current come through, but realistically, you can just think of this as being an open circuit. and it's going to block that current from coming through. The really nice thing about the schematic symbol or representation of diodes is that um you know it actually is just an

arrow that helps remind us what direction they go. So if the current's flowing in the same direction of the arrow, it's going to pass. Um and if it's coming into you know where we have this line that I kind of think of as

like the negative symbol or like a wall, it's going to block the current. So, this is really, really useful for helping us control the flow of electricity. And there's actually a lot of things that we use diodes for in

electronics. And I'm not going to go over all of them in this lesson, but just to get you kind of thinking about it. One really basic thing that we use diodes for is to protect our circuits from applying a backwards polarity or

backwards voltage to those circuits. So, we talked about, you know, different circuit elements like there's types of capacitors or even LEDs, which are actually a type of uh diode. They really don't like having the polarity swapped on them and putting voltage or current

the wrong way through them. And this is especially true also of lots of like digital components, which we haven't talked about yet, but things like processors or, you know, all the chips inside of our actual electronics, they really don't like having their polarity

swapped on them. And this can fry all of those components. And you've actually maybe done this before with like a remote or something else that has a battery where you put the battery um in backwards and you realize it was backwards, it didn't

work, but nothing bad happened. Switch the battery around and everything was okay. And one thing that may be happening in this circuit is that the designers added in some sort of reverse polarity protection and they used a diode to do so. So that if you, you

know, put the battery in backwards or you hook your voltage up the wrong way, what it's going to do is it's actually just going to block the current from flowing and it's just going to be like, uh, you know, an open circuit and no

damage will be done. So that is one way that we can use diodes. There's lots of science behind how do diodes work and we're not really going to get into that.

However, there are some specific characteristics about how they actually function uh, in the real world that we should take a look at. The way that we've been looking at them or talking about them in the last couple circuits

here is mostly as an ideal diode. And the next couple slides, we're going to take a look at how they actually function in real life.

All right. So, I've just rearranged the lettering on this schematic here just a bit. It's still the same circuit uh just to help identify this voltage here. So, the first characteristic that we're going to talk about is the forward bias

voltage. And what this means is, you know, previously we were talking about how if we hook the positive end of our diode up to the positive end of our voltage source, and of course the negative is connected to the negative or

ground, then we're going to be able to get some current. Now, in reality, this won't happen for all voltages. It's only going to happen if the voltage that we hook up is greater than what is called the forward bias voltage. And on most

standard diodes, this is going to be at about 0.6 volt. So once this voltage here, you know, we've got it at 9 volt, so that's not going to be a problem.

But, you know, if this were like 0.4 volts or 0.3 volt, then that's not going to be enough to, you know, the way I think about it is turn the diode on and go over that forward bias voltage and

actually allow current to flow. Now, in reality, it's, you know, it's not going to be exactly at 0.6. It's going to be, you know, kind of around there and there's going to be a kind of uh region in that where there's, you know, a bit

of current that can come through and as we get closer to 0.6 and go over it, it's going to um allow all that current to go through. But, you know, 0.6 is a pretty good threshold to think about.

And there are diodes where this is number is greater or smaller if we need them in our design. So, just keep that in mind. We're not going to look at those today, but you can get different diodes that have um different forward

bias voltages. The other thing to keep in mind with that forward bias voltage is that we're actually going to get uh you know a voltage drop over this diode when it's in that you know turned on state and that forward bias voltage is

actually going to be that voltage drop. So for example if we wanted to calculate the current that's going through this circuit this I1 then we would need to take that into account. Just some really quick math then if we wanted to

calculate that circuit we're going to have to go this 9 volts minus 0.6 6 V divided by the resistance. We're just using a little bit of Kaw's voltage law and Ohm's law here and we're going to get 8.4 milliamps. If you just do some

really quick top of the mind math for this, which is why I use the 1k resistor. If we didn't have this diode here, then we're going to have 9 volts over this resistor. And of course, we're going to have 9 milliamps. So, because

of this diode, we're actually going to have a small voltage drop a and a small little bit of less current than we would otherwise. Um, and depending on your circuit, maybe this really isn't going to matter at all. You know, if we're

operating at 9 volts, maybe that's not going to. Um, but for some electronics, especially where we're getting into logic levels at 3.3 volts, then you can start to see how this may be a consideration that you want to think

about. Okay, so the next important characteristic that we're going to talk about is if we flip this voltage supply and then we up the voltage. So we were talking previously about how if we put this voltage supply in backwards, we

have the polarity swapped and we have the positive end of the voltage supply hooked up to the negative end of the diode. We have current trying to flow backwards to the diode. It's going to block this current coming through. So in

a perfect world, it would just block this for all voltages. You know, in actual real life applications, the diodes, they can only withstand so much voltage before they're going to do what's called breakdown. And the voltage at which they do this is called the

reverse breakdown voltage. So, on a standard diode, looking at around minus50 volts. However, this one's, you know, not as standard as that forward um voltage drop or the forward bias voltage. So you really should be if you're concerned that you're going to be

getting to this level or you're designing um your circuit around this then it's really important to actually look at the data sheet for the diode and see what this is and what happens when we go over um that breakdown voltage. So

if our voltage in is you know in the backwards polarity and then it gets greater than that breakdown voltage we're going to have what's called the diode breakdown. And what's going to happen immediately is this diode is going to switch basically on and offer

almost no impedance um or resistance. So we're going to get the current rush right through it and then generally what's going to happen is it's going to fail. U it's kind of unpredictable about how it's going to fail but it's probably

going to like burn up and it may burn up into an open circuit or it may burn up into some kind of closed uh short circuit. It's really unpredictable. It's going to happen. But the important thing to remember is it's probably not going

to come back from this. It's going to be, you know, broken. It's going to be a burned out component.

So, we don't want to for most diodes be, you know, approaching or or going over that breakdown voltage. Now, there are some special types of diodes where we actually can um go into or over the breakdown region, and that's actually

their design of them. Um, but we're not going to talk about those today. But just something to keep in mind that there actually is diodes that can do this. However, most standard ones, you know, once we go into that breakdown

region, they're they're broken. They're going to burn out and be unusable. So, that kind of covers uh the basics of diodes in a DC circuit. We are going to take a look though at how they affect alternating current voltage sources. And

to do that, I think it's easiest to jump over into Circuit Lab. So, I'm going to hop over to Circuit Lab and I'll meet you over there. Now that we've popped over into Circuit Lab, let's take a look

at how diodes interact with alternating currents. So, we'll just start here with our alternating current voltage source.

I'm going to drop that in. And we'll leave it at 1 kHz sine wave. We'll just leave this all default at 1 volt for now.

Going to have a add a resistor. So, we've got a load that we can measure over. And then we will grab our PN junction diode. So, that's this one. And we don't need to worry about what that means, but we're just going to put it in

this direction with the polarity. And we'll connect these up with some wires here. Add in our grounds.

Then I'm just going to name these nodes so they make it a little bit easier for us. So, we'll call this one voltage in and we'll call this one voltage out or V out.

Okay. Now, same as before when we were working with the alternating currents, in order for us to see what's going on with these voltages, we're going to need to run a simulation. So, let's do that now. Put this back in the middle. All

right. We're going to do a time again and we'll set this actually since the waveform is much faster here. We're just going to do 10 milliseconds. And I'm still going to do a 10 microscond step time here. And we'll click on these

here to add our input and output voltages as expressions. And then let's run that time domain simulation. All right, perfect. So let's let's explain what's going on here. So this blue one again, this is our input voltage. So we

just have this perfect sine wave with a 1VT amplitude. And we'll see, interestingly enough, um, this is kind of the region where we're actually turning on the diode. And you can see that it's actually clipping quite a bit

of that signal because we have that for this diode, it's a between, you know, 0.6 and 0.7 volts that we're actually clipping off the top. And then once we go into this negative region, we don't get any because this is where the

diode's actually turned on. And then as we go back on again, we are still clipping. So I'm just going to hide this. This is kind of what we expected and shows how that diode needs that forward bias voltage and able to turn on

and how it doesn't let anything in reverse. Let's just hide this. And then let's jump this up just to get a better idea.

So I'm going to jump this up to 10 volts here. And then let's run the same simulation.

All right. And now we can see how our output voltage for the portions of the sine wave where it's in the positive region or the currents going in the positive direction, it's more or less unaffected. So we get that positive blip

and then we actually just get it turned off and we we cancel out the negative voltage portion of the wave or where the current would be trying to flow in the opposite direction. So for these periods here where it's negative I'll just hide

this. We would have the current trying to come back across this diode and it's not able to turn on. So what this is actually called really basic circuit this is called a halfwave rectifier because we have you know turned off or

rectified out half of that wave. Just want to show really quickly um just one thing for interest. If I go back to build here and if we grab a capacitor here actually and we put it in parallel, we'll just add a ground here.

And I'm going to put this up to 100 microfarad capacitor. So it's got a nice amount of ability to hold charge. And if we run this same simulation just really quickly using the same parameters, you can see now actually that we're, you

know, able to turn this what was a sine wave actually into getting close to being a DC signal here. And we're actually able, if we play around with the resistance values and the capacitance values to get this pretty

close to being a DC input. And so this is a halfwave rectifier with a capacitor filter in order to make this. Um, and this is actually somewhat of an inefficient way, but really cheap and easy way to turn alternating currents

into a DC signal. Uh, the reason it's inefficient is because we're just basically wasting all of the power in the second half or the second portion um of the period of the wave. But this is a really cheap and basic way that we can

create a DC signal. And you know, if you are interested in this or you want a little challenge for yourself, you can look up what's called a full- wave rectifier, which just takes a few more diodes in a capacitor. Uh, and it's a

much more efficient way. So, if you're curious about that, I would challenge you to, you know, Google the schematic for that and build it out in circuit lab and see how that works. However, for this lesson, hopefully that gives you an

idea of how diodes function and why they're so critical in circuits. I'm going to wrap up the video here and I'll see you over in the next one.

Welcome everyone. In this video, we're going to be chatting about transistors. So, this is actually the last electrical component that we're going to be talking about in the electrical engineering for hackers series, and we've arguably left the most important one for last. I've

heard a lot of people say or make the argument that transistors are the most important invention of the last century.

And to be honest, I would probably agree with them. More on that in a second. Up on the screen here, I've got the schematic representation or schematic symbol for one specific type of transistor that we're going to look at

in this lesson. And I've got two throughhole components of it right here. Uh this one is for larger power and current and it's got a heat sink. And then this is just a very very common throughhole transistor style that you

would see. And then of course these also come in a surface mount design. So in addition to those packages where we would actually be putting transistors into a circuit or onto a printed circuit board, we also use transistors to make

up the inside of, you know, processors. So inside, you know, your computers or your phones and the integrated circuits or processors in there, they are made up of millions to billions of transistors, which is actually kind of mind-boggling.

And to just kind of demonstrate how many they are, I've got a chart up here of Moore's law. Um, and Moore's law, it was it started out as kind of like a theory, but has turned into a law over time. And

it basically just says that every year, the maximum amount of transistors that we can fit on one of these IC's or a single wafer of silicone, the material that they're made out of, is going to double. And it became a law because over

time that actually did hold true. And you can see we've kind of got this linear progression over the years of the amount of transistors we can fit all the way up to this goes into 2018 and we're at about 50 billion here. Um and you

know now 5 years later I think we're actually close to 600 billion that we can fit which is pretty insane.

And the reason that these transistors are so important and allow us to make these computations uh in the CPUs or processors or these ICs that they're in is because one function of transistors is as a switch. And of course, switches

are very good way for us to electrically represent a one or a zero. They're either on or they're off. Now, this is an extremely complex subject chatting about the construction of processors um down to this level. And we're not

actually going to dig into that in this course. I just wanted to kind of show for interest and also my explanation of why transistors are so important. Just give you an idea of how they are used.

So we're actually just going to be looking at one specific type of transistor in this lesson and it is called an NPN bipolar junction transistor. You'll hear that referred to as BJT for short. And we'll chat more on

what NPN means in just a second. Now, one of the things you may have noticed with the transistor that's different from all of the different circuit components or electrical components that we have looked at so far is it's

actually got three leads or three inputs to it. But the other items like you know for example the resistors or the capacitors or even the diodes all of them just had the two leads and we inserted them in

our circuits so that you know they would have an input from one end and an output from the other and we'd have either a current or voltage come through them and they would you know change that in some

way uh and it would come out the other side. So at the most all we really needed to do was possibly label the polarity of our leads you know one positive one negative. So now that we've got three, this actually completely

changes um how this circuit componentry works. And in order to keep track of the different leads, we actually name them.

So in this layout, this NPN BJT, we have the top one is called the collector, the middle is called the base, and then the bottom is called the emitter.

So before we dig into what these specific pins do, I just want to give a quick overview of what the two basic functions of a transistor are. So the first main one that we already talked about is we can use it as a switch and

we can use it as an electric switch. So by varying the voltage that goes to the base. You know if we think of this as our switch or a valve, we can open it up all the way and allow a current to flow

through. And there's a lot of advantages to this that we'll talk about later. The other thing we can do is use it as an amplifier. So to use as an amplifier what we can do is we can open up if we

think of this as a valve open it up partially in such a way that if we apply a input signal to the base we can have that mirrored um to a greater voltage and current that is coming through the

collector and the emitter and and we'll chat about that more in depth in the coming slides.

We're not going to get fully into the nitty-gritty of how transistors work, but we are going to take a look at some circuits and talk more in depth about these two functions. So, if past this, you know, all of that isn't making

sense. The really the most important and two critical things that I want you to take away from this lesson is just that to remember these two basic functions of the transistor. And when you see them on circuits, you'll know that they're going

to be performing one of those two functions. Before we get into looking at some circuits and how these transistors actually work, just a quick note on some other schematic symbols that you might see. Um, so I chatted previously about

that last BJT transistor was in the NPN configuration. Well, we also have what's called the PNP and you'll see that we've flipped the emitter and collector and these function fairly similar to the NPN transistors. You know, a really

oversimplified way of saying it is that they just kind of work backwards to them. And then the symbol that we have over here, this is for what's called a field effect transistor. And we're not going to actually talk about those uh in

this lesson, but I just wanted in case you run across a symbol to understand what they are. Um, and they have their own different designations for the pins.

So the top one is a drain, middle one is called the gate, and then this bottom one here, S, is called the source. And you might hear these referred to as MOSFETs as well. And that MOSS, it just

stands for the uh how what they're manufactured of. Again, we're not going to talk about these any more in depth in this lesson. I just wanted to make sure you're aware of if you saw the symbols for them that these are what they are.

So, as long as you understand the core functions of a transistor and what they do, then you know that core functionality or or concepts, they're going to apply uh to these as well. And then it's just really the implementation

of them that's going to differ. One of the best ways that I find to describe transistors and to visualize how they work is to go back to this water analogy. And I've I've got our transistor up here on the screen just so

I can set up this analogy and we can see what the different parts of the transistor and circuit are with regards to our water analogy. So the first part is our voltage supply here. We've got this giant tank with the water held up

high. That's going to represent our voltage um that will allow this water to come down through this pipe. Second thing is we've got this other big uh container here. We'll think of this as our ground that can, you know, receive

an infinite supply of this water. At the top here, the pipe that's connected to the voltage supply is our collector. And at the bottom, this section of the pipe here is the emitter. And then we've got this valve in the middle that I'm going

to call the base. So, if you think of this as like if we turned it kind of like you would open your hose, um then that would allow this valve to slide open and let some water through. Now

that we've got the analogy set up, I just cleared the arrows away to make it a little bit easier to see. So if we were using this transistor in its switching format or as a switch, then what we would do is apply a voltage to

the base and we would apply that voltage in such a way that it's going to cause the base to fully open up its valve. So when we do that, of course, all of the water is going to rush through this pipe

and it's going to go down to the ground. So, if we compare that to our transistor here, we apply that voltage. And we'll chat about what that needs to be later.

Um, but when we apply the correct voltage, that's going to put it in what we call the active region and fully open. We can think of that as, you know, if this was our valve, it's going to fully open and instead of water, we're

going to get the theoretical maximum amount of current that's going to be pulled from our voltage source uh down to the ground. And of course, the amount of current is going to be dependent on how we design our circuit and any

resistors that we place in the way. So that's how we use it in the switching setup. So the other setup is that we can actually use it instead as an amplifier.

You'll see here I've changed the image so that you know we've cranked this open, but we've only cranked it open halfway. And this is how we use as an amplifier because there is a region of operation of the transistor that we're

going to chat about a little bit more where depending on the voltage that we apply here, it's only going to open this flow partially and that is going to be proportional to the voltage that we input. And that's how we use it as an

amplifier by kind of sliding open and close this valve to let a certain amount of that water or current come through um that is proportional to the input. but of course much bigger in scale. So with that water analogy out of the way, let's

take a look at kind of like a pseudo circuit of how we could, you know, use a transistor to do this. And I'm going to call this a pseudo circuit cuz we have no resistors yet in our circuit here,

which you would generally want to add some in because if you actually were to, you know, hook up your transistor like this, then it would actually uh just catch fire because there would be no current limiting. get infinite current

and it would just burn up our transistor. So, what I've done is I've hooked the top of our transistor to VCC. Um, and we haven't really chatted about what VCC means, but you'll see this on a lot of

electronics uh schematics. And what that means is it's like the nominal operating voltage of the circuit. For example, the power supply to our router is 9 volts.

So, the BCC for that or the standard operating voltage would be 9 volts. And then this VN, we're just, you know, this is just a signal that we're going to be taking into the base. Okay. So, I've added in a couple voltage nodes here

just to make it a little bit easier to understand how this transistor um functions. So, the first one here, this is the voltage at the base. And then we've got the voltage at the emitter here. And if we were to measure the

voltage in between these, it's called VBE. Now, when you look at this transistor, you may have noticed that this symbol, it kind of looks like a diode right here. And that's because for the operation of this transistor, we

actually can think of this as being a diode. And the way that transistors actually are created is is kind of similar to putting two diodes together um back to back. And then the voltage that we apply to the base of it, it will

actually change the function of this diode and allow current to come through. So you may recall from our previous discussion on diodes that there is this forward bias voltage that we need to surpass in order for that diode to open

up and and that's how we use the transistor as a switch. What we need to do is set up our circuit such that this VIN is going to cause the the voltage at the base to make this VBE be greater

than whatever that threshold is. So, you know, for most transistors and diodes, it's around that um.7 volts or 700 molts. And once we go past that region, it's going to fully open up this section of the circuit. And it's going to allow

our current, you know, that's being driven by this VCC voltage to flow through our circuit. So, for a switching circuit, what we were just talking about, the thing that we have to remember is that we designed the circuit

such that this VN uh it pushes the BBE into what we call the active region. And that active region of the transistor is when it is fully open. So for amplification, you know, the one thing that you may recall from our diodes

lesson is there's actually a region of operation of the diode where it's not actually fully open or fully closed. It is, you know, partially open. And in this region is called the saturation region. This is how we can do that

amplification that we talked about where varying this input voltage is going to vary the amount of current that we allow through this diode. And in order to do that, what we have to do is we have to design our circuit. So for an

amplification circuit such that this VBE fluctuates in the saturation region or in that region where the transistor is going to allow an amount of current to flow through that's proportional to the signal that we input. And the way that

we actually set up our circuit to to do that and to you know hold this VBE in that 7ish range is that we do what's called biasing the transistor. And we do that by tying uh the base up to the VCC

through a set of resistors. So if we need to divide the voltage or just straight through a resistor and we have some voltage drop over that resistor and we can then tie this VBE to that saturation region and then our voltage

signal can just ride on top of that and cause that fluctuation that allows us to have the amplification.

Now the design of circuits around transistors and biasing them and you know the different configurations of hooking them up it actually can get quite complex and I'm not going to specifically go into that uh in this course because you know as hardware

hackers I think it's really just important for us to understand kind of how these transistors are used and when we see them in the circuit we can understand that okay yeah this is being used as a switch or this is being used

as an amplifier. we don't actually specifically need to know how to design them. Now, if if you do want to learn this, then that's great and there are a lot of awesome resources on the internet for them. However, for

our example, I think, you know, taking it to this point uh is good enough. With that being said, what I am going to do now is I'm going to hop over into Circuit Lab and I will create two

circuits, you know, actual circuits with resistors and signals to demonstrate how we can actually build out an amplifier or a switch. So, I will hop over there now and I'll see you there.

Welcome everyone. So, that last video on transistors was getting too long to be one lesson. So, I split it into two videos. And in this video, we're going to take a look in Circuit Lab at some transistor circuits. So, without further

ado, we'll jump right over into Circuit Lab right now. Okay. So, this first circuit that we're going to take a look at here is just really a demonstration one to show how we can actually drive this transistor into the active region.

It's not really a good representation of how an actual circuit would work, but I think the outputs from it uh really help to understand how changing this input voltage can actually trigger or change the amount of current that we let

through. So, just to really quickly show what we've got going on here, we've got our voltage source up here at 24 volts.

Uh, and we've got a current limiting resistor here. And if we look at just that DC, we can see that we have uh 237.3 milliamps. So, the reason we don't have that full 240 milliamps is that because is that's because we actually do have a

small voltage drop. Um, what's from what's called the uh VCE or the collector to the emitter. And if we hover over the transistor, we can actually see that that is 265.1 molts. So that's where we lose that little bit of current from. Just keep in

mind, so theoretically our max current that we can have come through is that 237.3 milliamps. Now I've got a node here representing the base voltage. And we can see here I have applied um this signal voltage and it is a sine wave at

1 kHz. So I just click on it quickly so that we can see the properties of it.

You'll notice I have a 5V ampl amplitude, but I do have a DC offset of 5 volts. So just if you're following along, the reason I've done this is that way it's not actually going to bounce from minus 5 vol to 5 volts. I just want

this to actually um start at a positive value and only stay um in the positive range cuz it really helps to demonstrate how this transistor functions.

And what I want you to think about is, you know, this is not an actual um representation of what you would see in a real life circuit. And and don't really think about this as like a signal or anything we're trying to amplify. I

really just wanted an alternating current that shows what happens with our transistor and how we can use it in this switching region as the input voltage changes. So let's take a look with a quick simulation. So let's leave these

parameters here. These are the standard ones we've been using. And then what we're actually going to be plotting is I'm curious about the current that we can have come through here and then also this base voltage.

All right. So let's just run this time domain simulation here. Perfect. So this gives us actually a really great representation of how the voltage change is actually going to you know open up this transistor.

So we start here. Um you know because of that offset we're actually starting at 1.2 2 volt, but we can see at 1.2 volts here, we're at that theoretical max of the current that we are going to be

letting through. So that's at that 237 milliamp region. Uh, and of course, as our voltage increases over time, we're still over that um region that's going to open up the transistor. And as such, our current is all the way at that 237

milliamps. And then you'll notice here once we get right around this region um right here right around 700 that 700 molts or 7 volts we actually drop off we drop off very quickly. Um and once we get below that 7 volts our current is

all the way down at essentially zero. Uh and as the rest of this signal changes through here we are at zero. And it's not until we just kind of breach that 7 uh.7 volts or that 700 mill volts that we actually go

back up into that active region. And when we're in that active region, so we don't care now that we're above that active region what that voltage as high as it goes. We're all the way open already at 237

milliamps. So if I just hide this quickly then. So what that means is that you know we we have a lot of sensors and outputs from microcontrollers um where the voltage we can control how that changes and that's really great because

then we can design our circuits so that you know as that sensor changes or that voltage output from our microcontroller changes we can use that to drive this and then open it up as we like. I'll give a couple of real life examples here

just so it helps make sense why we would actually want to do the switching in the circuit. So the first one is if we take that example of a photo resistor where the resistance value changes based on the amount of light that's shining.

Well, we could make a light that turns on once that photo resistance value gets below a certain level. And this is how a lot of um light sensing circuits work.

And in that scenario then once the resistance value is changed enough by the light we would design our circuit so that it will fully open uh up the transistor and then it can power a light and turn on that light. Another example

is if we actually think about that uh smart lock that we were talking about in the very first section of this course.

You know if you enter in your pin through the smart lock and then it's going to unlock. There's likely going to be some sort of microcontroller, microprocessor that's going to have some logic um that outputs on a pin that

digital out as a high or a low. That means that the lock should unlock. And when we do that, the current and voltage that's going to come out of that microcontroller or microprocessor is not going to be powerful enough that it

could actually drive uh you know any kind of mechanical movement where we actually need to you know physically move something to unlock that door. So, one way that we could do that is with a transistor uh and have the transistor

and you know this VCC or whatever this voltage be set up so that the current and voltage that's supplied when it's in that fully switched on mode would be enough to drive that mechanical motor or whatever we need. And then we tie that

pin from the microcontroller down to the uh base of that transistor. And we design our circuit such that when the logic says that the correct pin is open, it will set the voltage to open up that switch. All the current will come

through and drive that mechanical motor. And that's how we do this actual switching. So again, you know, in this example, don't think of this as an input. Um, I just really wanted to show how that voltage changing over time can

impact the transistor and cause it to kind of open and close in that switching region. Going to just open up another circuit here and we'll take a look at a very basic amplifier.

Okay, so I've got another basic circuit opened up here and this is what we call a common emitter amplifier because we actually just have the uh emitter of this tied down to the common ground. And we're looking at this circuit and it can

be a little intimidating looking at it at first. So what we'll just quickly do is break it down into the few different regions. So what we've got here is this is uh actually this sign voltage is representing um an input voltage that we

would be measuring. So if we just take a quick look at it, you'll notice that I actually have the amplitude set at 5 molts. This is a very very um weak signal and maybe it would be something that would come from like a microphone

if we were um measuring sound through a microphone. You'll notice we have this capacitor here and we already talked about uh capacitors and the reason that we have this what's called a coupling capacitor here is because we want to set this VB

uh so we're in that saturation range and in order to do that we can't have any fluctuations in the voltage other than what is actually coming from this sine wave. Now in circuit lab this doesn't really matter because this is actually

like a a perfect sine wave. But in reality we might have some DC uh leakage coming in and we want this this capacitor is just going to block all that from coming. So the next section of the circuit we'll look at is this one

right here. So we're actually using 5 volts as our our VCC here. Um so what we're going to do is we're going to you know amplify this 5 molts with that 5V signal. And in order to get this VB so

that it's going to be sitting right around that 700 molt or.7 volt sweet spot, we're going to steal some of this voltage up here uh and tie it down here.

And that's where this RB or the the base resistor comes in. We also have this RC which is the collector resistor. And this is what's going to um set the amount of current that comes through here to amplify. And

if you want to learn more about how to calculate these to get it in this region, then you know there's lots of really good videos or resources uh about that. But this would turn into a really long lesson if we talked about that. So

I'm just going to leave it at that. You know, these values I've pre-calculated them using some formulas and some characteristics of this transistor. Uh and you know, if we really want to go into that, it would make this video way

too long. The last section of this circuit here is just this one where I'm simulating uh a load with this resistor. And I'm coupling again with a capacitor to remove the DC bias from the circuit so that that we're actually only getting um

you know the pure AC signal coming out. So if we run this simulation, let's just run a time simulation. And because we've got some capacitors, I I want to look at it in its steady state and, you know,

ignore um the initial power on of this circuit. So, I'm just going to start at 100 milliseconds and then go from 100 milliseconds to 110 milliseconds. And we will still use that 10 microcond step.

And we're going to take a look at the output voltage. Of course, we'll take a look at the input voltage. And then we will also take a look at the base voltage. So, let's run that time simulation. Um, and this one's just

going to take a little bit longer since we're starting at that 100 milliseconds. Okay, so this graph is actually a great representation of how our amplifier works. Now, the one thing that I should mention is that a common emitter

amplifier is actually what we call an inverting amplifier. And what that means is that our waveform is going to be flipped. Um, so here when we're at our peak of our input, you'll notice that we flipped it and we have a negative here.

And if this is going to be a problem for our circuit, you know, depending on our signal, some signals it is, some it isn't. Uh, what we can do is we can add another transistor that we can flip it

back again as needed. But for this one, just to keep it simplified, um, we'll just look at it in its inverting state.

So this orange signal right here, this is our input signal. we can see, you know, how weak of a signal that is. We just have that 5 m volts peak. Um, and it's honestly so weak we can barely even

see it on this graph. So, what I've done here with the transistor base voltage is we can see how by pulling it up into that, you know, 730ish molt region or that 7 volts is putting us right in that saturation sweet spot.

and we're just riding right around where we're able to partially open and close that transistor. And what that's doing is it's allowing uh you know a portion of that BCC voltage to come through. And you can see by doing that we've actually

amplified if we look at our peak voltage here you know right around that 5 volts.

That's about as close as I can probably get it. So we're going from almost 5 molts to about 710 molts. We're looking at about 100 almost 140 times amplification which is pretty good and I think right around the maximum of what

this transistor is capable to do. So this is how we can use these transistors to actually you know bump up weak uh input voltages from our sensors and we can actually then you know make them more useful to read them.

So hopefully this gives you a little bit of an idea about how transistors work.

Again, this is a very um complex subject and you could spend a lot of time, you know, hours and hours even learning about just the basics of this. So, if there's really just, you know, two things you take away from this lesson

and that's it, it would just be to remember the two basic functions of transistors in that we can use them uh as a switch. So, we can take a smaller input voltage into the bass and then have them to control a much higher

voltage and current or we can use them as an amplifier again to put a weak signal or lower voltage signal into the base and then have that open up partially open up and close the transistor in such a way that we can

create a amplified version of that signal passing through the transistor and use that to amplify weak signals. So that wraps up our lesson on transistors.

I will see you over in the next one. Welcome everyone. In this video, we're going to be talking about electronic communication and signals. So right now for you to be watching this video, there is dozens and dozens of different

electronic communication and signal paths taking place. Of course, the obvious one is that we've got the network traffic going over the internet and streaming this video data. However, also internally, if you're watching this on your computer um or a tablet or

something like that, on the motherboard of your device, there is all kinds of different communication signals that are taking place just internally between the different componentry uh on your device and then also out to your monitor for example. So, we can split up electronic

communication and signals into two main categories. And the first one is as analog signals. and we're not really going to focus a lot on them, but I just want to make you aware that this is one way that we can actually do

communication. So, here's an example of one of the analog signals that we were talking about previously. And we'll just say that it varies in voltage and also frequency to represent a sound signal.

And the way that this works is with a microphone, the vibrations that sound make can actually then be translated into a varying voltage. uh and the amplitude and frequency of that signal changes with respect to the sound and

then we can actually play that back through a speaker which is just actually a microphone in reverse and it will play that sound and we can transmit this signal over a wire and have someone play it back to themselves. So this is like

one of the very earliest uh types of analog communication when we first invented the phone and it was as basic as that. We may have some components in between to either amplify the signal like transistors that we were looking at

or other amplification devices and maybe some capacitors or other things to do filtering. But the signal is continuous and there's you know there's no designation of anything like bits or anything like that. We just have a continuous voltage signal. So for this

course we're not really going to be working much with analog signals. we're going to be more concerned about those signals that are actually internal to our devices and going between the different componentry and those will generally be digital signals. And we've

looked at this already. Instead of, you know, having this continuous sine wave that represents some sort of signal, we use a square wave or an on andoff pattern to toggle the voltage between some low value and a high value. So,

generally that would be like 0 volts and then 5 volts. Um, and if we're reading on that line, then we read a 5 volts, we know that that is a one. And if we read the low, then we know that's a zero. And

this is really the, you know, the basis for all digital communication. Even if, you know, we start thinking of like these higher up, more advanced protocols. If we peel them, you know, all the way back down to at their very

very most basic level, you know, even if you're thinking of, for example, the OSI model, if you're familiar with that at layer 1, then this is really just, you know, voltages on a line or voltages on a wire. And this is one of the important

things that I want to drill home for hardware hacking and we're kind of getting into this hardware mentality is that when we boil these protocols, you know, right down to the very basic like there's still they're a voltage signal

and you know, even though it's not analog in the terms of, you know, we have this fluctuating sine wave, this is still a square wave of alternating current and it still behaves as such.

So, if we're crafty enough as hardware hackers, then, you know, there's some things that we can do just at the hardware level without even thinking about software, knowing that this communication is actually really just voltages being applied to a wire. So, to

make sure that we all have a baseline of how these digital communications work and that we can build up on, I want to just introduce and maybe we can try and come up with our own very very basic

method of doing digital communication uh with hardware. So I want to introduce just you know a super basic circuit here. We have this is our our voltage rail and I have it labeled as V LH. So that LH that stands for logical high. So

when the voltage is at this voltage level and we don't really care what it is. Could be 3.3 volts, 5 volts. I mean we can make it whatever we want cuz we're making up this you know little protocol ourselves here. And then I've

got a switch. We've got a resistor here of course just because we don't want to uh have voltage without a resistor. then we're going to, you know, be putting way too much current through and burn out the wire. We don't really care about the

resistors, but that's why it's there. We have a switch here, so we can toggle on and off that voltage. And then we have this receiving pin that we can put out.

Um, so it'll be transmitting from this end, and then someone could hook up even just a multimeter to this and read out.

Uh, and then if we go slow enough with our switching, they could actually decode our message. So, let's pull up a graph of what this uh receiving pin would look like. I'm just graphing this, you know, really basic over time, the

same way we've been looking at it. Um, so this is the voltage at this pin here or this output. Uh, and then I just have this labeled as this logic high to make it really easy for us to read when we

have ones and zeros. So, if we close the switch, then we know just, you know, really basic Kra's voltage law, then what we're reading out here is going to be the same as this VLH. So, of course, we get our voltage up here and the

person who's reading on the other end can say, "Yep, okay, we've got a one." And then if the next thing we want to transmit is a zero, then we just throw open the switch. And you see here our

voltage drops down to zero and we know we've got a zero. So, the great thing about this is that, you know, all we really need to exchange at this point or all we have is that we'll just determine what we're

considering to be a high and a low. So in our example, we're saying that you know this VH whatever it is be 3.3 volts or whatever that's going to be our high and then if we get a zero volts or

around zero then that's going to be zero. So in reality we'll generally have two thresholds you know an upper limit threshold and a lower limit threshold.

Um and when we go above that upper limit threshold that will be considered a high and when we go below that lower limit threshold that will be considered uh zero. And this just gives us some breathing room in our circuit if we

have, you know, any tolerances or things like that that throw off the voltage levels. I just left them out of this cuz I think it's cleaner to look at it like this. We'll just assume that we can do

those perfect voltage levels. Okay. So, in this example, what happens if our transmitter, so whoever is operating this switch has decided they would like to send another zero. So, they leave the switch open, send another zero. Of course, as time passes, we still are

just at that zero volts. Whoever's reading, if they're just doing, you know, the most basic reading ever, they just have a multimeter here. They're still reading zero.

How do they know that I'm sending another zero and not it's just a continuation of that same zero, right?

So, when we look at this graph, it's, you know, it's kind of obvious because you're saying, well, we held this one for the same amount of time, then we held this zero for the same amount of time. So, it would be assumed um that

this would be held for the same amount of time. And really that that is the foundation of how we're actually going to get past this issue in that we're going to set a specific amount of time that we're going to hold each symbol.

And that is called the symbol duration. And we represent that generally with this t subscript s. And what that really says is just you know each time I transmit a symbol in our case it's just going to be bits. So a one or a zero.

I'm going to hold that for a set amount of time. And that way if I transmit you know multiple of the same symbol one after another and you you know kept transmitting zeros then the person on the other end is going to be able to

decode that. So for example if we're just you know really basic math every second we're going to send a new symbol.

So the person on the other end would go you know 1 second that's a one next second that's a zero. Next second that's another zero. When we set up these parameters and you know exchange that we're going to be communicating at with

these different symbol durations, we generally don't actually say the symbol duration. And the reason for that is these get you know very quick. We're not going to be doing 1 second. It's going to be down you know into the

milliseconds or microsconds. So we're not going to say you know for example oh the symbol duration is going to be 0.1 microsconds. So instead we'll generally communicate this to be the amount of symbols per second that we can do. And

as long as we're me measuring our symbol duration in seconds, then to get that, we just go one over the symbol duration.

So one over t subscript s. And the name for this, there's actually a name for this. We call it the baud rate. So the baud rate is the amount of symbols per second. Now in our example, again, our

symbols are just ones and zeros. So we could call this a bit rate. And sometimes you will see it referred to as a bit rate because realistically now in modern communication is pretty much always going to be ones and zeros and

bits, but the industry standard is still usually to call baud rate. So keep that in mind. I'm going to use baud rate cuz that's what you'll usually see. You may also see it referred to as speed or the

communication speed. So just keep that in mind that you may see either one of those. Okay. Okay, so just to bring this full loop now that we've kind of established what our communication protocol is going to be and that we're

going to send, you know, one bit one after another and we're going to have a high voltage level represent a one, a low voltage level represent a zero. And we're going to send each bit with a specified duration. So we can just say 1

second here. And I put these ticks on the graph to separate that. So we can think of these each as 1 second. So let's say we want to transmit high. this t subscript x that stands for tx and

then the same for rx. So the way that we can do this is we can send you know h and i asy characters.

All right. So the asky representation for h in hex is 0x48. And then if we convert that to binary then it's just 0 1 0 0 1 0 0. So I can transmit onto that line out like an actual, you know, low

voltage level, high voltage level, low, low, high, low, low. Right? And you're getting the gist. And then the person reading that is able to, you know, read that and then they can decode that back from that binary to the hex to the ASKI

and see, okay, that's an H. And then we can send an I. So the hex representation for I 0x49. Again, we're just adding one um bit to this. So we're just going to be adding a one on the end. We can just

transmit this again, right? And then the person receiving they'll receive that as an I. And we have sent a very basic H and I.

When we're sending data like this, you know, eight bits and we're sending it grouped together like this for one representation, then generally what this is referred to um in this digital communication in this basic format like that is called a frame. So if you're

familiar with networking then you maybe heard of a packet. So at you know layer three at the network layer what we call like that grouping of data is a packet.

Well at layer 1 it's actually called a frame. And then even outside of the OSI model just at these you know basic communication protocols where we're just looking at um the voltage on a line and then building up off of that. You know

this grouping of data we call a frame. So, for those of you that are following along at home, you may have noticed that, you know, we still have some glaring problems in our communication protocol. The first, you know, and maybe

most obvious one is if, you know, let's just say I'm sitting in one room, someone else is sitting in another room.

We've run a wire to them. Um, you know, and I have a switch that I'm going to open and close it, and they're sitting on the other end, and they've got their multimeter, and they're going to measure the voltage. Um, and when they see that

voltage high on the multimeter, whether it's 5 volts, uh, and then when they see it zero volts, they're going to, you know, know it's a one and a zero, and then they can decode that. So, as a good

example, our very first, you know, symbol or bit that we want transmit is a zero. Well, how do they know that I'm starting to transmit? I mean, if I'm just sitting here with the switch open, um, you know, am I sending zeros all the

time? When is when does the transmission start? So, there's one problem. The other problem is, you know, how do we tell when a frame ends or like how long a frame is is always going to be eight?

You know, how how are we going to determine um that, you know, all of this is the H and then it doesn't flow into this one. And then also, what if that person wants to send us back? We just

have this one wire now. So, I mean, are we going to add a second wire? Are we going to, you know, have some sort of way to say, I'm done with the line. It's your turn. There's a lot of different

things that we need to kind of sort out. And this is where the various different protocols um that communicate in this method are going to come in play. And they all have their own ways that they kind of solve these issues. And we have

predetermined things that we agree on or you know set ahead of time between the receiver and transmitter in order to fix these issues. And we're going to build on you know these very basic core concepts of our baud rate and this

voltage and toggling the voltage on the line uh throughout the rest of the course when we look at those.

So the other glaring problem that we have and you know this is just kind of a problem with this style of transmission is that we're limited to just sending this one bit one after another. And when we do that what this is called and

you've probably heard this before is this is called serial communication. And that's literally what serial means. It just means we're sending one bit or one symbol one after another. And this brings us to limitation of speed. you know, we're really just limited um to

how fast we can actually, you know, turn on these symbols on and off. So, in our example at 1 second, like that's horrible. It'll take forever. Um but even, you know, as we increase the speed to what is really, you know, capable of

devices to be able to read and transmit, it's going to become a limitation for bandwidth that we just have to send all these symbols one after another.

So, what we can do to get around that is we can use what's called parallel communication. And in parallel communication, instead of us sending, you know, on one line, one bit after another, we can open up multiple lines

and we can send, you know, all of that information in parallel to each other.

So that's why it's called in parallel. Um, you know, so if we just take our example again where we want to say hi.

So first we're going to send the H. So before we decode this and actually look at these voltage levels, the other thing with parallel communication that I want to bring in is um you know before we were using a speed but what happens you

know we're all if we set say we're all at a speed but what if we don't start um at the same time right then we can start to get uh our pulses of communication be off from one another. So in parallel

communication, we also always will generally bring in a clock and that clock will allow us to synchronize and make sure um that all of our communication pulses are together. And the way that the clock works is going to

differ between, you know, different protocols. But in this one that I'm just kind of making up to demonstrate uh how parallel works, we'll just say that we're going to sample um on the rising and falling edges of the clock. And

you'll notice that the clock is offset from the actual communication. Um, and that's so that we we're going to force it to sample in what would hopefully be the middle of a transmission. And this way we have the best chance of actually

being able to capture what, you know, each of these symbols are supposed to be because if it's shifted, you know, left or right a little bit, that's still going to be okay.

So on our rising edge of the of the clock, we would sample that. Um, and in here, we're going to get, of course, that 0 1 0 0 1 0 0. And that's going to make up an H. So instead of you know

ascending it one after another if we were just using one channel instead we've sent them all in parallel and essentially you know even if we were doing this just at one second you know we have times 8 our bandwidth right or

times 8 our speed because we can you know send this at one time and if we want to send our I then on each channel we would then reend our bits again we have 0 1 0 0 1 0 0 1 and this would make

up an I. So the main difference between parallel and serial that I I want to make sure everyone understands because it can kind of get a little bit confusing for some of the serial protocols is that you will

see them start to have you know multiple lines and they still may use a clock um for synchronization.

But the really big differentiator of what still makes those serial is that even if we had four channels, you know, and we were talking serially, each of those channels would send all of their data or their frames on one channel. So,

you know, channel zero's data would not be intermixed with channel one's data. Whereas in parallel data, you know, each of these frames are split across each of the channels. Um so this whole frame is taken up by all of these channels and

that's what is considered to be this parallel communication. So in this course we're mostly going to be working with serial communication.

It's actually still you know very very commonly used for a lot of protocols and especially the protocols for our different components and chips on our device to talk to each other. That wraps up this lesson and actually wraps up our

theory section for electrical engineering for hackers. So, I'll see you over in the next section where we're actually going to look at our very first serial protocol on our board. Um, and we're going to hook up to that and start

doing some readings on it. So, I'm looking forward to that. I'll see you over in the lab when we take a look at that. Hey there. Hope you're enjoying the course. We'll get back to it really quickly. But before we do, I wanted to

call out again to just make sure you are subscribed both to my YouTube channel, which I'll link down below and also to the TCM Security YouTube channel, this one that you're watching the video on.

So, I would really appreciate it if you just take a second and check. Make sure you're subscribed and if not, hit that subscribe button for us. Thank you.

Welcome everyone. In this video, we're going to be continuing on our learning about digital serial communications by taking a look at UART. So, UART is a type of circuit or a functionality of a piece of hardware that allows us to do

asynchronous serial communication. UART itself is not actually a protocol. All it does is it just sets out a method that allows us to asynchronously basically transmit ones and zeros using electricity between either, you know, two circuits or two pieces of hardware.

So, we're going to start today's lesson by taking a look at what UART stands for and how the connections for it work. And then the rest of the lesson is going to be hands-on, which is why I've got the

router and the multimeter here. So, if you are following along at home, you'll need both the router and multimeter as we're going to then be taking a look at how we can identify the UART connection on this router and verify the pin out

for that connection. So, I'm just going to move these to the side for a second here so we can chat a little bit about UART.

UART stands for universal asynchronous receiver transmitter. And I'm just going to chat quickly about what each of these words mean in our acronym here. So universal, that's because this is a universally and widely used method for asynchronously transmitting uh serial

data. It's very very widely used. It's it's quite an old method, but you will still see it frequently used on electronics and come across it in hardware hacking. So asynchronous means that we have no clock synchronizing between our two devices that are

communicating each other. So the transmission and receiving do not have to happen on a clock signal and there's no shared clock. What we do need to do though, similar to that previous serial protocol that we were kind of making up

in the last lesson, is agree on a baud rate or speed that we're going to be transmitting at. So the receiver can then decode those transmissions.

And then the receiver transmitter. This one's pretty straightforward. It just stands for that the devices are able to both receive and transmit.

Now I've drawn out two devices here so we can look at the pin outs for standard UART and how they're connected. So I've got device A here and device B. So generally with UART communication nowadays, it's going to be handled by a

functionality uh of a processor or some other integrated circuit. So that's why just at its very very base level I've drawn these as chips eight pin chips and generally you're going to have you know many many more pins on the chips and

you'll have to look at the pin outs for them to see what pins are used for UART and just to simplify it I've just drawn it you know as these eight pin chips. So just to keep in mind also when you're

looking at this on a circuit generally you're going to have you know this soldered to a PCB and then we'll have traces that go off somewhere maybe to a header or other connections for these pins. So UR generally is going to have

four pins and they're going to be the TX pin and TX stands for transmission, the RX pin where RX stands for the receiver.

Then we'll have a ground and a VCC. So just like the TX pin you would expect it to be. This is the pin that transmits out. So, if we want to send out our serial communication, uh, we're going to

send out those voltage levels and those voltage pulses that we looked out on the transmit pin. The receive pin is we're just going to listen on this pin and measure for changes in voltage levels.

So, if we are to hook up uh another devices's transmit pin to this receive pin, then we're just going to sit and we'll hold this voltage level here on this until another device is going to uh put it high and then we can read.

We have a ground because for this serial communication to properly work, we need to make sure that both the devices are sharing a common ground. And the reason for that is we need to make sure that both devices are able to accurately

measure what that high voltage level is. You know, generally it's going to be 3.3 or 5 volts. So let's just use 3.3 volts for this lesson. You know, if this device is going to be transmitting and reading 3.3 volts, we need to share the

same reference to measure it from. So they're both on the same page. Finally, we have this VCC for supplying power. And this is generally not used especially in hardware hacking. But where we can use this is if we need to

supply power from one device. So for example the device A to device B. We could hook this VCC pin up and then supply power to a device that doesn't have its own power supply. So an example of where you might use this is if you

know you have a sensor or something like that that's using UART communication to send back its data and it's just a small sensor. It doesn't have any power. then we can hook up the VCC and grab some power off that. So, I'll just really

quickly draw up the lines here to show how generally we hook up two devices.

The transmit from one device, it actually goes not to the transmit of the other device, of course, but it goes to the receive. So, it's going to go to the receive here.

And then the opposite is true from the other device. transmit would go here and then it would come over to this devices receive.

We're going to hook the grounds together. So, that one's nice and easy. And then the VCC, I'm just going to draw an X here. And generally, what X stands for is no connection. So, we don't actually need to connect those on most

applications. And for what we're going to be doing in this course, we can just leave the BCC unconnected. So just one other quick note here on the transmitting and receiving functions of these devices.

Depending on how the designer of the software that's running on these devices and the circuitry that they are using, sometimes they'll only just be designed either to transmit or receive. So for example, maybe we don't want to actually

take in any commands or anything like that on the rece pin. So, it will either just, you know, it won't be connected at all to a header or maybe the software is just going to ignore whatever is on that

pin and we'll only just transmit data out. And the the opposite is true. Maybe we won't actually transmit anything out and we're just going to be listening to receive data. It's also up to the designers of the circuit to determine

whether or not we're going to allow both devices to communicate at the same time.

So UART will allow for this just on how it's set up and with having these two separate lines. We can actually have both devices. So device A and device B transmitting and receiving at the same time. However, it's going to depend on

how the software is set up whether or not what it's going to be expected is for example for device A to send out a message and then it won't transmit. It will wait until it receives some sort of

message back from device B. Some protocols enforce this, but remember UART itself, it's not actually a protocol. It's really just a method for us to essentially send ones and zeros from one device to the other device. And then what we do with those

ones and zeros is really up to the designers of the circuit. whether or not they build a protocol out on top of that or they just use it to send raw data or raw messages like we saw in our last

example where we just use the ones and zeros to send asy characters and that allowed us to send a message. This should give us enough information now that we can set this aside and we can take a look at our router PCB and try

and identify the UART connections on there. So, when I'm starting to do some initial recon on a device that I'm going to be testing or doing some sort of hardware hacking on, the very first thing I look for is a UART connection.

And now, to me, they stand out like a sore thumb when I see them because they're generally a really good source of lowhanging fruit for us or an easy win to get a foothold or some sort of information from the device. Now, the

UART connection here is this is right here. We've already taken a look at it.

And what we're generally looking for is some sort of connector or pads or through hole like we have on this device where there's four of them in a row like this. And that doesn't necessarily always signify it's UART, but it's a

really good spot to start. Now, on this device here, it's actually really good for us. They've labeled the pin out for us. You can see here we have the VCC, the ground, the RX, and then the TX pins

already labeled. So, this is a really, really good indicator that it is going to be UART. Now, on most devices, they're not going to make it this easy for us. Generally, they won't actually be labeled with a silk screen. So, what

we need to learn how to do is identify which of these pins are which and actually be able to check and see if this is a UR connection. And we can do that with just a multimeter.

Another thing that I will say also is even though these are labeled, it's still a really good practice to check our voltage levels and check the pins and make sure they actually match. Later on in this course, we're going to be

using this UART connection to connect back to our computer. And when I connect anything to my computer off of circuitry, I really like to check the voltage levels and make sure everything is okay because I don't want to damage

my computer. Luckily, from the previous lessons in this course, we already have all the skills that we need to test these with our multimeter. So, I've got it right here. The first thing that we're going to test with it is I've just put this on

the continuity setting, and we're going to double check and make sure that this this one, which is labeled ground, is actually a ground connection. You may remember, we actually already tested this, so we're going to do it quickly

here again. But we also identified this little bare metal pad right here that's denoted with, I believe, a P1. This is a ground connection as well. So, we can just check the continuity really quickly between the ground and this P1.

So, for continuity, the polarity doesn't matter. So, you can touch either one of the leads to each one. We need to touch one lead to this P1 here and then the other one to ground.

And I immediately get a beep. So that's perfect. We know that this one is in fact a ground. Now to test these other pins, we're actually going to be measuring the voltage levels. So what we need to do is go ahead and plug in the

router. And I'm going to do that right now. Okay. So I've powered on my device here and we see that it's looks like it's stabilized in its boot up. And I've just brought my multimeter up a little bit

closer so that it's in focus and easy to see the voltage we're reading. And I've switched it to the DC voltage setting here at 20 volts. So you'll want to do the same if you're taking this measurement.

The first thing we're going to check is the VCC voltage. And what that's going to do is give us an indication of what voltage level the UART is operating at.

We're expecting to see either 3.3 volts or 5 volts here. So to measure that again, we can just do from the VCC pin here with the red lead to that same ground that we've been using.

And if I hold this on here tightly, we get that perfect at 3.3 volts.

Perfect. So we know that that BCC pin is labeled correctly and we're operating at 3.3 volts, which is important to check.

The next pin that we're going to check is the RX pin. And we know that this one should be 0 volts because we're only going to be listening on it. So when we measure the voltage at this one, we're

going to be expecting 0 volts. So in the same manner as the VCC, we'll check the RX pin here.

Perfect. It's right at 0 volts and that is what we're expecting. The next pin that we're going to check is the TX pin.

So unless we happen to catch a transmission, which is pretty unlikely just during this regular operation, then we're expecting to see this at 3.3 volts. So let's check that now.

Perfect. Right at 3.3 volts. Okay. Okay, so you may be wondering if these weren't labeled, how can we tell the difference between which one is the VCC and the transmit?

So what we can do is we can force a transmission on the board. And the easiest way to do that is actually just to reboot the router or, you know, unplug the power supply, replug it in.

You ever watch like your BIOS on your computer when you're starting up? There's a lot of messages that come through. There's a lot of logging that takes place right at startup. there's a lot of important, you know, messages

printed out. And that's the same with this router as well. If we unplug it and then reboot it up, we should be able to see a bunch of transmission taking place. So, what I'm going to do is I'm

just going to unplug this and then plug it in. And then pretty quickly, I'm going to try and probe the transmit pin again so we can catch those boot up messages. And what we'll be looking for is we'll be looking for that 3.3 volts