**What is Signal? — Transcript & Summary | SozAI**
Source: https://sozai.app/transcript/what-is-signal/

Introduction to signals in digital electronics, covering definitions, examples, and the role of signals in electrical and electronic systems.

## Key Takeaways

- A signal is a time-varying function representing physical quantities, especially in electronics as current or voltage.
- Constant electrical quantities like direct current are not considered signals because they do not vary with time.
- Transducers play a crucial role in converting between electrical and non-electrical signals.
- Understanding signals is foundational for studying digital electronics and signal processing.
- The video sets the stage for deeper exploration of analog, discrete, and digital signals.

## What the video covers

- Definition of a signal as a function representing variation of a physical quantity with respect to an independent parameter, usually time or distance.
- Explanation of dependent and independent variables using a mathematical function example.
- Real-life example of measuring temperature over time to illustrate signal plotting.
- Discussion on the shape of functions such as parabolas and straight lines based on coefficients in the function.
- Clarification that in electrical and electronics, signals typically represent variations in current or voltage over time.
- Distinction between signals and direct values, such as direct current which does not vary with time and thus is not a signal.
- Introduction to transducers as devices converting non-electrical signals to electrical signals and vice versa.
- Example of a microphone converting sound energy to electrical signals, amplification, and speaker converting back to sound.
- Mention of various types of signals and a preview of upcoming topics: analog signals, discrete time signals, and digital signals.
- Emphasis on the importance of signal variation for it to be considered a signal.

Answers

## Questions about this video

What is a signal in the context of digital electronics?

A signal is a function that represents the variation of a physical quantity, typically electrical current or voltage, with respect to an independent parameter such as time.

Why is direct current not considered a signal?

Direct current remains constant over time and does not vary, so it is not considered a signal because a signal must vary with the independent quantity.

What is the role of a transducer in signal processing?

A transducer converts non-electrical signals into electrical signals, and the reverse transducer converts electrical signals back into non-electrical forms, enabling signal processing and communication.

## Full Transcript — Download SRT & Markdown

00:05

Speaker A

lecture in the digital electronics course, and this course is also called as digital logic or digital logic and designing in various colleges.

00:16

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The name is not important, the name of the subject is not important, but the content is, and the content is going to be same.

00:26

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Almost same in all of this courses.

00:30

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So you can start from here, we will first see what is a signal, then we will see what is an analog signal.

00:41

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A discrete time signal and then we will see what is a digital signal so that we can start our digital electronics course.

00:50

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So let's move to the signal, what it is.

00:55

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A signal is a function that represents the variation of a physical quantity with respect to any parameter.

01:02

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This any parameter is the independent quantity.

01:10

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And it is generally time.

01:15

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Or distance.

01:17

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So the function is definitely dependent upon this independent quantity.

01:24

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And I hope you already know about the function from your mathematics course.

01:31

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But we will also see one example that will clear these things more.

01:35

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So let's say my function is F.

01:40

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And as it is dependent upon the independent quantity, and I will say my independent quantity is X.

01:48

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Then I will write it as F(x).

01:52

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This shows that this function is dependent on the X.

01:56

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And let's say it is equal to -ax^2 + bx + c.

02:00

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Now this is my function.

02:04

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And I will try to implement this function in a daily life example.

02:10

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For this, I will take a boy.

02:13

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Let's have a boy and this boy will do a work for us.

02:16

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He will go to a particular place and measure the temperature from morning 9:00 a.m.

02:22

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to the evening 9:00 p.m.

02:25

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So he's having his thermometer, he will stand there.

02:30

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And he will measure the temperature in every one minute.

02:33

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So I can say he will have a data at the end of the day from 9:00 a.m.

02:40

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Then 9:01, 9:02, like at 9:00 a.m.

02:46

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He's having 27 degrees Celsius.

02:50

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Then 9:01 is having 27.5 degrees Celsius.

02:53

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In the same way, he will have the different temperature for different time till the 9:00 p.m.

03:00

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So this is his task.

03:02

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And he will have a data, he will have a list of the temperatures for a different time.

03:08

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Now what we can do with this information?

03:10

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We can plot it.

03:12

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So let's try to plot it.

03:16

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And you already know that this X-axis we use for the independent quantity.

03:22

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And this Y-axis we use for the dependent quantity.

03:26

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And in this case, the independent quantity is time.

03:30

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Definitely, the time is independent.

03:34

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I will represent it by small t.

03:37

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And this axis will represent my temperature.

03:42

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T, capital T is my temperature.

03:46

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And as it is dependent on the time.

03:51

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I will write T here.

03:53

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Now we can plot these values.

03:55

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Let's say our origin is 6:00 a.m.

04:00

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And this point is 11:00 p.m.

04:04

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This is 9:00 a.m.

04:06

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And this one here is 9:00 p.m.

04:09

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So we will just show the temperature for the different times.

04:14

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And let's say it comes like this.

04:17

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And then we can join these points.

04:21

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And we will have our function like this.

04:24

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So this particular function is the downward parabola.

04:29

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And it is having the equation like -at^2 + bt + c.

04:34

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This -a shows that we will have a downward parabola.

04:39

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And there is one condition for that.

04:42

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This A must be greater than zero.

04:45

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If this A is equal to zero, we will have a straight line.

04:50

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Because T will be equal to bt + c.

04:54

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This is the equation of a straight line.

04:57

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Y = mx + c.

05:00

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This C is the intercept.

05:01

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And if this A is less than zero, we will have the upward parabola.

05:06

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The upward parabola.

05:09

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So this is a little bit about the functions, you have already learned these things in your mathematics.

05:15

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Back in the 11th standard.

05:18

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So we'll not go much into that.

05:20

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And finally you can have your signal.

05:22

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This one, this function is your signal.

05:24

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You will have the values of the temperature for the different time and that is what the signal.

05:31

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You will have a pattern that will tell you how the temperature has been changing.

05:35

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From 9:00 a.m. to 9:00 p.m.

05:38

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So this is what you have to remember about the signals.

05:41

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Now I will narrow down this study of this signal.

05:46

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And I will talk specially about the electrical and electronics.

05:52

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And in electrical and electronics, usually the signal is the variation of the electrical quantity.

06:00

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Generally current or voltage with time.

06:02

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So it's important to write this thing.

06:06

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And let's write it down.

06:10

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In electrical and electronics.

06:16

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Usually, usually signal is variation.

06:21

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Of electrical quantity.

06:26

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Generally current or voltage.

06:30

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And what is the independent quantity in this case?

06:33

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The independent quantity is time.

06:35

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So this variation of electrical quantity, generally current or voltage.

06:41

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Is with time.

06:44

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So this is something you have to keep in your mind.

06:50

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And there is one very important point that you must know.

06:55

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If the current or the voltage remains the same for different time, then it is not a signal.

07:04

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It is a direct value.

07:07

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For example, if I talk about the current.

07:11

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The current.

07:14

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And if current is same for the different time.

07:20

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Then it is direct current.

07:23

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It is not a signal.

07:25

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It is a direct current.

07:27

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And we can say dI, the small change in the current is equal to zero.

07:30

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The current is not changing.

07:33

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And you can plot it simply like this.

07:36

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The current at T1, let's say this is T1 is I naught.

07:40

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And current at T2 is also I naught.

07:43

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So the current is not changing.

07:45

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It is a direct value.

07:48

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And thus it is not a signal.

07:50

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Signal must vary with the independent quantity.

07:54

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And let's talk about the transducers.

07:56

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A little bit.

07:58

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So the transducers are the device which is used to convert the non-electrical signal to an electrical signal.

08:04

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And the reverse transducer is the device that is used to convert the electrical signal to the non-electrical one.

08:10

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And let's see one example for it.

08:12

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If you are singing a song.

08:14

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You require a mic.

08:16

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This one is the mic.

08:20

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Okay.

08:22

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And you are singing near to it.

08:26

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So that your sound is converted to the electrical energy.

08:30

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This sound creates some vibration and that vibration is converted into the electrical pulses.

08:35

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And that electrical pulses is amplified, there is a device that we call as the amplifier.

08:40

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Because definitely it is required to amplify the signal so that it can be converted and interpreted well.

08:46

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So we have an amplifier.

08:48

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And once this amplifier is there, it will amplify and then you have a speaker.

08:55

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The speaker is there.

08:57

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And then again the sound energy is given back.

09:00

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So sound energy is given in, it is converted to the electrical energy, it is processed well.

09:07

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And then again it is given back as the sound energy by the means of the speaker.

09:11

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So this is how the signal works.

09:13

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And it is a very small explanation for the signal.

09:18

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There are so many hundreds and thousands of types of signal available to us.

09:23

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And we have just saw one example for the temperature.

09:28

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Now in the next presentation, we will see what is the analog signal.

09:33

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And the discrete time signal.

09:38

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Then finally we can have our digital signal.

09:40

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So this is all for this presentation.

09:43

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See you in the next one.

Topics: signal digital electronics analog signal discrete time signal digital signal transducer current voltage temperature measurement electrical signal

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