investigatory projects class 12

1. 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.

2. 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

3. 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

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

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

7. Realisation of OR gate

8. 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.

9. 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.

10. 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