 Hello everyone, myself Sanjay Udge, Assistant Professor, Department of Electronics Engineering, Valchen Institute of Technology, Solapur. Today, we are going to discuss Introduction to the Free Plots. Learning outcomes. At the end of this session, students will be able to describe working of various free plots. Outline. Introduction to digital electronics. In this, we are going to discuss analog signals, digital signals, logic gates, then question also, combinational circuit, sequential circuit, SR flip flop, and finally references. Before going to this flip flop, we must have a knowledge of analog and the digital signal. Signal is a time varying quantity that can carry information. A signal is a function that conveys information about the behavior or attributes of some phenomenon. Analog signal is a continuous signal. It is represented by a sine wave described by the amplitude, period or frequency and the phase. Analog signal has no fixed range. It is more prone to distortion. Here is the waveform of analog signal. It is a sinusoidal alternating quantity. It is having a maximum value plus 5 volt and negative maximum minus 5 volt. It means that this analog signal will have values ranging from 0 to 5 volts. In other words, it will have values, for example, 0.1 volt, 0.2 volt, 0.3 volts, 4.99 volts and 5 volts. So, it is an example of a continuous signal. This is a digital signal. Digital signal is a discrete type of signal. It is having only two values, either 0 volt or 5 volt. This square wave is the best example of a digital signal. It is having 0 volts, which is called as logic 0 and 5 volts, which is called as logic 1. Some characteristics of digital signal. It has a discrete value that carries information in binary form. A digital signal is represented by square waves. It is described by bit rate and bit intervals. It has a finite range that is between 0 and 1. A digital signal is less prone to distortion. It carries data in binary form that is 0 and 1. Signals used for transmission in a computer. So, this is all about the digital signal. So, this is the differentiation between the analog and the digital signal. Analog signal, as we discussed, it is a sinusoidal quantity. It is a continuous signal. Whereas, a digital signal is a discrete type signal having values either 0 or 1. So, a digital signal can be represented by a stream of bits in terms of zeros and ones. A digital system stores data in a discrete form that is in a digital form. The opposite is an analog signal which stores the data in a continuous way. A digital system stores the information in a binary way. That is, every bit of information cannot have a value other than 0 or 1. Next, after discussion of analog and digital signals, we are going to discuss logic gates. It is logic gate. It is a basic building block of a digital circuit. It is an idealized or physical device implementing a Boolean function. That is, it performs a logical operation on one or more binary inputs and produces a signal binary output. It is an electronic circuit having one or more than one input and only one output. The relation between the input and the output is based on a certain logic. So, these are the symbols and the output expression for the basic and the universal gate. On the left hand side is the inverting buffer. On the left hand side, it is an inverting buffer. It is a not gate. The input is A. The output is the complement of the input. That is A par. The next below gate is the AND gate. It is also a basic gate. The inputs A and B. The output is A dot B. So, the output of the AND gate is Y is equal to A dot B. This is the Boolean expression for the AND gate. The next basic gate is the OR gate. The same A and B inputs. The output is A plus B. On the left hand side, you will find the left hand side top. It is a NAND gate. The two NAND gates, its Boolean expression is A dot B bar. It means that NAND gate is a combination of AND gate and followed by a NOT gate. So, AND gate output is AB A dot B. After this, we are giving this input to a NOT gate. So, finally, the NAND gate will have output A dot B bar. Here, both the inputs of NAND gates are shorted. So, it will have only one input A. So, the output of the first NAND gate, when the inputs, two inputs are shorted, the output will be A bar. So, by shorting the two inputs, we can get the NOT gate. NOT gate using a NAND gate. The next below figure is having the first NAND gate. Normal NAND gate having A and B inputs, whose output is AB bar. It is given to an inverter since a second NAND gate, its inputs are shorted. So, output is AB. So, with the help of this circuit, we got a AND gate. The third circuit is having first and two input NAND gates. They are in the NOT gate. So, A will give A bar, B will give B bar. A bar and B bar are given to third NAND gate. The output will be A plus B. So, in this way, on the left hand side, first top, middle and the lower one, these three circuits were implemented basic gates using universal gates. So, this is the NAND gate. So, let us have a look at the truth table. The truth table gives the information of the output depending on the various input conditions. So, A and B are the inputs queues the output. For 0, 0, output is 1. And for 0, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0. It means that 1, 1, if the inputs are 1, 1, output will be 0. For remaining three combinations, 0, 0, 0, 1, 1, 0, all the output will be hard. Exercise the assignment. What will be the output of NAND gate? If both inputs are equal to 1. Second question. If both inputs are different, that is, one input is 0 and other is 1. These are the answers. The output of a NAND gate, if both the inputs are equal to 1, the output will be 0. Second question. If both inputs are different, that is, 0, 1, 1, 0, it is the output will be 1. Combination circuit. It is a time-independent logic which is implemented by Boolean circuit where the output is a pure function of the present input only. So, this is the example of Adder circuit. Having A, B, C as the inputs to OR gate, S is the summation. So, the sum, it will have Boolean expression A plus B plus C in. So, these are some characteristics. Combination circuit. Output is a time-independent. It depends only on the level present at the inputs. So, combination circuit don't use any memory. Combination circuit can have a number of inputs and a number of outputs. Again, time-independent circuit. Sequential circuit is very important as far as flip-flop is concerned. Sequential circuit use current input variables and the previous input variables. So, it requires a memory as to store the present state. So, the next state will be dependent on the present state and the previous state. External outputs. So, this is the sequential circuit. Having a combination logic circuit which is time-independent, the combination logic circuit have an external input shown at the left-hand side top and another input is the previous input shown by green color. That is from memory. Memory will store a previous state. And finally, the output of the commonly circuit will be an external input and the previous output. Flip-flop. The two-stable circuit called as a latch used to store a single-bit information. It's having two states by a stable multivibrator. It can change state by signals applied to one or more control inputs. And will have one or two outputs. It's the basic storage element in the sequential circuit. It's a fundamental building block of the digital electronic systems used in computers communication and many of other systems. So, this is the SR flip-flop. The SR flip-flop is derived using a NAND gate and NAND gate in terms of the NAND gate. So, we will find out on the left-hand side top and bottom these two SNR inputs given to a NAND gate in the form of NAND gate. Next two stages of NAND gates will have output Q and Q bar. This SNR the inputs. For input 00, the output will not change. So, for example, if S is 0, R is 0, output will be same as that of the previous output. So, I can set here is a two-table shown below. So, for S0, R0, the output will be same as that of the last values. Next, if S is equal to 1, R is equal to 0, the Q will be 1 and Q bar will be 0. This is called as a set state. The third one, the third combination, when S is 0, R is 1, the output is Q0 and Q bar is 1. This is called as a reset state. And the last one, when S is equal to 1, R is equal to 1. When both are 1, the output Q and Q bar, they will try to become 1 simultaneously, which is not a valid state. So, this is the fourth one is a illegal state. So, these are the references I have taken. Thank you.