Logic Gates : Physics Investigatory Project
Project Report on Logic Gates:
The Logic Gates are constructing blocks at digital electronics. They are utilized in virtual electronics to exchange on voltage stage (enter voltage) into some other (output voltage) in line with a few logical announcement bearing on them.
A logic gate is represented as a virtual circuit which follows a few logical courting between the enter and output voltages. It is a virtual circuit which both allows a sign to skip through a forestall, it’s far called a gate.
A common sense gate may have one or more inputs, but it has best one output. The relationship between the viable values of input and output voltage is displayed within the form of a desk referred to as reality desk or table of mixtures.
The truth table of a Logic Gates is a table that shows all the input and output opportunities for the logic gate.
Any Boolean algebra operation can proceed correlated with inputs and outputs represent the statements of Boolean algebra. Although these circuits may be multiple, they may all stand constructed from three primary devices. We have three different types of logic gates.These are the AND gate, the OR gate and the NOT gate.
LOGIC STATES 

1 
0 
HIGH 
LOW 
+ve 
ve 
ON 
OFF 
CLOSE 
OPEN 
RIGHT 
WRONG 
TRUE 
FALSE 
YES 
NO 
TYPES OF GATES
There are three types of basic logic gates which follows a Boolean expression.
1) OR Gate
2) AND Gate
3) NOT Gate
1.) THE OR GATE
THE OR GATE is a device that combines A with B to give Y as a result.
The OR gate has two or more inputs and one output. The logic gate OR gate with A and B input and Y output is shown below:
In Boolean algebra, addition symbol (+) is referred as the OR. The Boolean expression:
A+B=Y, indicates Y equals A OR B.
2.)THE AND GATE
THE AND GATE is a device that combines A with B to give Y as the result.
The AND gate has two or more inputs and one output. The logic gate of AND gate with A and B input and Y output is shown below:
In Boolean algebra, multiplication sign (either x or.) is referred as the AND. The Boolean expression:
A.B=Y, indicates Y equals A AND B.
3.) THE NOT GATE
THE NOT GATE is a device that inverts the inputs. The NOT is a one input and one output. The logic gate of NOT gate with A and Y output is shown below:
In Boolean algebra, bar symbol (_) is referred as the NOT. The Boolean expression:
X’ =Y, indicates Y equals NOT A
Theory and Construction:
An OR gate can be obtained by the electronic circuit, making use of two diodes D1 and D2 as shown in the figure.
Here the negative terminal of the battery is grounded and corresponds to the 0 level, and the positive terminal of the battery (i.e. voltage 5V in the present case) corresponds to level 1. The output Y is voltage at C w.r.t. Earth.
The following interference can be easily drawn from the working of electrical circuit is:
If switch A & B are open lamp do not glow (A=0, B=0), hence Y=0.
If Switch A open B closed then (A=0, B=1) Lamp glow, hence Y=1.
If switch A closed B open then (A=1, B=0) Lamp glow, hence Y=1.
If switch A & B are closed then (A=1, B=1) Lamp glow, hence Y=1.
Truth Table:
Input A 
Input B 
Output Y 
0 
0 
0 
1 
0 
1 
0 
1 
1 
Theory and Construction:
An AND gate can be obtained by the electronic circuit, making use of two diodes D1 and D2 as shown in the figure. The resistance R is connected to the positive terminal of a 5V battery permanently.
Here the negative terminal of the battery is grounded and corresponds to the 0 level, and the positive terminal of the battery (i.e. voltage 5V in the present case) corresponds to level 1. The output Y is voltage at C w.r.t. Earth.
The following conclusions can be easily drawn from the working of electrical circuit:
 If both switches A&B are open (A=0, B=0) then lamp will not glow, hence Y=0.
 If Switch A closed & B open (A=1, B=0) then Lamp will not glow, hence Y=0.
 If switch A open & B closed (A=0, B=1) then Lamp will not glow, hence Y=0.
 If switch A & B both closed (A=1, B=1) then Lamp will glow, hence Y=1.
Truth Table:
Input A 
Input B 
Output Y 
0 
0 
0 
1 
0 
0 
0 
1 
0 
1 
1 
1 
Theory and Construction:
A NOT gate cannot be realized by using diodes. However an electronic circuit of NOT gate can be realized by making use of a n pn transistor as shown in the figure.
The base B of the transistor is connected to the input A through a resistance Rb and the emitter E is earthed. The collector is connected to 5V battery. The output Y is voltage at C w.r.t. earth.
The following conclusion can be easily drawn from the working of the electrical circuit:
 If switch A is open (i.e. A=0), the lump will glow, hence Y=1.
 If Switch A is closed (i.e. A=1), the lump will not glow, hence Y=0.
Truth Table:
Input A 
Output Y 
0 
1 
1 
0 
Theory and Construction:
If we attach the output Y’ of OR gate to the input of a NOT gate, the gate obtained is called NOR.The output Y is voltage at C w.r.t. Earth.
In Boolean expression, the NOR gate is expressed as Y=A+B, and is being read as ‘A OR B negated’. The following interference can be easily drawn from the working of electrical circuit is:
 If Switch A & B open (A=0, B=0) then Lamp will glow, hence Y=1.
 If Switch A closed & B open (A=1, B=0) then Lamp will not glow, hence Y=0.
 If Switch A open & B close (A=0, B=1) then Lamp will not glow, hence Y=0.
 If switch A & B are closed then (A=1, B=1) Lamp will not glow, hence Y=0.
Truth Table:
Input A 
Input B 
Output Y 
0 
0 
1 
1 
0 
0 
0 
1 
0 
1 
1 
0 
Theory and Construction:
If we connect the output Y’ of AND gate to the input of a NOT gate the gate obtained is called NAND.
The output Y is voltage at C w.r.t. earth.
In Boolean expression, the NAND gate is expressed as Y=A.B, and is being read as ‘A AND B negated’. The following interference can be easily drawn from the working of electrical circuit:
 If Switch A & B open (A=0, B=0) then Lamp will glow, hence Y=1.
 If Switch A open B closed then (A=0, B=1) Lamp glow, hence Y=1.
 If switch A closed B open then (A=1, B=0) Lamp glow, hence Y=1.
 If switch A & B are closed then (A=1, B=1) Lamp will not glow, hence Y=0.
Truth Table:
Input A 
Input B 
Output Y 
0 
0 
1 
1 
0 
1 
0 
1 
1 
1 
1 
0 
Theory and Construction:
The operation EXOR (Two AND gate, an OR gate, two NOT gates) checks for the exclusivity in the value of the two signals A and B. It means if A and B are not identical (i.e. if A=0 and B=1 or vice versa), the output Y=1, and if both are identical, then the output Y=0. This operation is also called exclusive OR gate, designated EXOR.
In Boolean expression, the EX OR gate is expressed as
Y=A.B + A.B =
The following interference can be easily drawn from the working of electrical circuit:
If both switches A&B are open (A=0, B=0) then lamp will not glow, hence Y=0.
If Switch A open B closed then (A=0, B=1) Lamp glow, hence Y=1.
If switch A closed B open then (A=1, B=0) Lamp glow, hence Y=1.
If switch A & B are closed then (A=1, B=1) Lamp will not glow, hence Y=0.
Truth Table:
Input A 
Input B 
Output Y 
0 
0 
0 
1 
0 
1 
0 
1 
1 
1 
1 
0 
Theory and Construction:
The procedure EXNOR (Two AND gate, an OR gate, three NOT gates) checks for the exclusivity in the value of the two signals A and B. It means if A and B are not identical (i.e. if A=0 and B=1 or vice versa), the output Y=0, and if both are identical, then the output Y=1. This operation is also called exclusive NOR gate, designated EXNOR.
In Boolean expression, the EXNOR gate is expressed as
Y=A.B + A.B =
The following interference can be quickly moved from the working of an electrical circuit:
a) If Switch A & B open (A=0, B=0), then Lamp will glow, hence Y=1.
b) If Switch A closed & B open (A=1, B=0) then Lamp will not glow, hence Y=0.
c) If Switch A open & B close (A=0, B=1) then Lamp will not burn, thus Y=0.
d) If switch A & B both closed (A=1, B=1) then Lamp will glow, hence Y=1.
Truth Table:
Input A 
Input B 
Output Y 
0 
0 
1 
1 
0 
0 
0 
1 
0 
1 
1 
1 
Some Common Applications of Logic Gates
Application of OR gate
Anywhere the existence of any one or more than one event is needed to be detected, or some actions are to be taken after their occurrence, in all those cases OR gates can be used. It can describe as an example. Suppose in an industrial plant if one or more than one parameter exceeds the safe value, some protective means is needed to do. In that case OR gate is used.
Application of AND gate
There are mainly two applications of AND gate as Enable gate and Inhibit gate. Enable gate means allowance of data through a channel and Inhibit entrance is just the reverse of that process, i.e. unacceptable of data through a channel. We are going to show an enabling operation to understand it more naturally. Suppose in the measurement of the frequency of a pulsed waveform. For analysis of incidence, a gating pulse of known frequency is sent to enable the passage of the waveform whose rate is to be measured.
Application of ExOR/ExNOR gate
These type of logic gates are engaged in the generation of parity generation and checking units.