What is Signal?

welcome to the first lecture in the digital electronics course and this course is also called as digital logic or digital logic and designing in various colleges 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 almost same in all of this courses so you can start from here we will first see what is a signal then we will see what is an analog signal a discrete-time signal and then we will

see what is a digital signal so that we can start our digital electronics course so let's move to the signal what it is a signal is a function that represents the variation of a physical quantity with respect to any parameter this any parameter is the independent quantity and it is generally time or distance so the function is definitely dependent upon this independent quantity and I hope you already know about the function from your mathematics course but we will

also see one example that will clear these things more so let's say my function is f and as it is dependent upon the independent quantity and I will say my independent quantities X and then I will write it as F X this shows that this function is dependent on D X and let's say it is equal to minus of a X square plus BX plus C now this is my function and I will try to implement this function in a daily life example for this I will take a boy let's have a boy and this boy will do a walk for us

he will go to a particular place and measure the temperature from morning 9:00 a.m. to the evening 9:00 p.m. so he's having his thermometer he will stand there and he will measure the temperature in every one minute so I can say he will have a data at the end of the day from 9:00 a.m. then 901 902 like at 9 a.m. he's having 27 degrees Celsius the 901 is having 27.5 degree Celsius in the same way he will have the different temperature for different time tillie and 9 p.m. so this is his task

and he will have a data he will have a list of the temperatures for a different time now what we can do with this information we can plot it so let's try to plot it and you already know that this x-axis we use for the independent quantity and this y-axis we use for the dependent quantity and in this case the independent quantity is time definitely the time is independent I will represent it by small t and this axis will represent my temperature T capital T is

my temperature and as it is dependent on the time I will write T here now we can plot this values let's say our origin is 6 a.m. and this point is 11 p.m. this is a 9 a.m. and this one here is 9 p.m. so it will just show the temperature for the different times and let's say it comes like this and then we can join these points and we will have our function like this so this particular function is the downward parabola and it is having the equation like minus of a

t-square plus BT plus C this minus of a shows that we will have a downward parabola and there is one condition for that this a must be greater than zero if this a is equal to zero we will have a straight line because T will be equal to BT plus C this is equation of a straight line y equals to MX plus C the C is the intercept and if this is less than zero we will have the upward parabola the upward para bola so this is a little bit about the functions you have already

learned these things in your mathematics back in the 11th standard so we'll not go much into that and finally you can have your signal this one this function is your signal you will have the values of the temperature for the different time and that is what the signal you will have a pattern that will tell you how the temperature has been changing from 9:00 a.m. to 9:00 p.m. so this is what you have to remember about the signals now I will narrow down this study of this

signal and I will talk especially about the electrical and electronics and in electrical and electronics usually the signal is the variation of the electrical quantity generally current or voltage over time so it's important to write this thing and let's write it down in electrical and electronics usually usually signal is variation you can see here we are having the variation of the temperature with time in the same way we have the variation of the electrical

quantity and this electrical quantity is generally generally current or voltage and what is the independent quantity in this case the independent quantities time so this variation of electrical quantity generally current or voltage is with time so this is something you have to keep in your mind and there is one very important point that you must know if the current or the voltage remains the same for different time then it is not a signal it is a direct to volume

for example if I talk about the current the current and if current is same for the different time then it is then it is direct current it is not a signal it is a direct current and we can say di this small change in the current is equal to zero the current is not changing and you can plot it simply in like this the current at T one let's say this is T one is I naught and current at T two is also I naught so the current is not changing it is a direct value and thus it is not a

signal signal mast where I with and the independent quantity and let's talk about the transducers little bit so the transducers are the device which is used to convert the non electrical signal to an electrical signal and the reverse transducer is the device that is used to convert the electrical signal to the non electrical one and let's see one example for it if you are singing a song you require mic this one is the mic okay and you are singing near to it so that your sound is

converted to the electrical energy this sound creates some vibration and that vibration is converted into the electrical pulses and that electrical pulses is amplified there is a device that we call as the amplifier because definitely it is required to amplify the signal so that it can be converted and interpreted oh well so we have a amplifier and once this amplifier is there it will amplify and then you have a speaker the speaker is there and then again the sound energy is given back so

sound energy is given in it is converted to the electrical energy it is processed well and then again it is given back as this sound energy by the means of this speaker so this is how the signal works and it is a very small explanation for this signal there are so many hundreds and thousands of types of signal available to us and we have just saw one example for the temperature now in the next presentation we will see what is the analog signal and the discrete-time

signal then finally we can have our digital signal so this is all for this presentation see the next one