Sound Operated Light

While living in rent or in hostel the problem like stealing is often in absent time. Here is the circuit of simple and inexpensive sound – operated light to overcome this type of problem which can turn on the light when someone claps, or tries to open your door or even inserts a key in the door lock. The switching of light is alternately i.e. light on by one sound pulse and off by another. It is also called clap operated light or clap switch.

Circuit Description of sound operated light

The entire circuit of sound operated light is designed and builds around an operational amplifier IC (IC1) and JK flip-flop IC (IC2). The sound coming from outside is senses by microphone and converts it to corresponding electrical signal where sensitivity of sound is controlled by potentiometer VR1. The high value of reference voltage is given to pin 3 of IC1 in order to change the output voltage from pin 6. Here IC2 (JK flip-flop) is wired as a toggle flip-flop and its output is connected to relay driver transistor T1 through resistor R1 which energized the relay RL1 when sound is heard by microphone. The bulb from sound operated light is connected to AC source through relay contact as shown in circuit diagram.


Resistors (all ¼-watt, ± 5% Carbon)

R1 = 22 KΩ

R2, R5 = 1 KΩ

R3 = 470 Ω

R4 = 10 KΩ

VR1 = 10 KΩ


C1 = 0.1 µF

C2 = 470 µF/35V


IC1 = µA741 (operational amplifier)

IC2 = CD4027

T1 = 2N2222

D1, D2 = 1N4001


X1 = 230V AC primary to 0-9V, 250 mA secondary transformer


(110V AC primary to 0-9V, 250 mA secondary transformer)

RL1 = 12V, 200Ω, 1C/O Relay

SW1 = ON/OFF Switch

F1 = Fuse

MIC = Condenser Microphone

Bulb 230V, 60W (110V, 60W)

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