Aim

To understand the working of OR gate using p-n junction diodes and to design a circuit of OR gate using diodes, LED, push button type toggle switches and suitable resistances.

Introduction

OR gate is an Boolean operator based on the mathematical function of addition.

It works on digital signals as its input which have only two states of voltages, low as 0V and high as 5V.

OR gate consists of electonic circuit of p-n junction diodes having two input digital signals which can take four different combinations on voltages, for each combination of voltages there is a predefined output according to addition rule.

Apparatus used

p-n junction diode (IN 4007)

Circuit board

Wires

9V battery and battery connector

LED (5mm, 1.5V)

Resistors

Push button type toggle switch

Push buttons

Theory and working

1.)Working of p-n junction diode in forward and reverse biasing

2.)Understanding the functioning of OR gate and its realisation

Realisation of OR gate

3.)Circuit diagram used in making of OR gate and its working

For first circuit

When the push button is in ‘released state’ then terminal ‘2’ is connected to terminal ‘3’, when push button is in ‘active or pressed’ then terminal ‘2’ is connected to terminal ‘1’.

The push button connected to first diode is ‘button 1’ and the other one is ‘button 2’.

When ‘button 1’ is released and ‘button 2’ is released then it is equivalent to A(0), B(0). In this state, first diode is reverse biased and second diode is reverse biased, current does not flow through LED.

When ‘button 1’ is pressed and ‘button 2’ is released then it is equivalent to A(1), B(0). In this state, first diode is forward biased and second diode is reverse biased, current flows through LED, through first diode.

When ‘button 2’ is pressed and ‘button 1’ is released then it is equivalent to A(0), B(1). In this state, first diode is reverse biased and second diode is forward biased, current flows through LED, through second diode.

When ‘button 1’ is pressed and also ‘button 2’ is pressed then it is equivalent to A(1), B(1). In this state, first diode and second diode is reverse biased, current flows through LED, through both diodes.

Conclusion

The output of OR gate for four combinations of inputs clearly shows the expected output according to the truth table.

Sources of errors

Write yourself

Precautions

Do not connect any electronic component without resistance in series, it can burn the component.

Bibliography

NCERT textbook of class 12

Physics by S.L.Arora

Circuits available on internet