Various type of switching circuit like touch operated relay, light operated relay, heat operated relay is already posted in bestengineeringprojects.com. Now here is one another simple electronic project in the series of switching circuit called sound operated relay.
Circuit Description of Sound Operated Relay
The circuit of sound operated relay is self explanatory and is very easy to understand. This circuit is build around 2-stage audio amplifier using PNP transistors. The sound sensor of the circuit sound operated relay is done by 8Ω loudspeaker. The output of loudspeaker is given to the base of transistor through audio transformer X1 for amplification. The amplified output is give to the input of darlington pair build around transistors T3 and T4.
As long as sound wave is present, the darlington pair remains conductive and the drop across collector and emitter of the transistor T4 become very low i.e. the load is energized. And as the sound wave disappears, the load is de-energized.
Given configuration is for load power up to 2W and for more load power up to 9W the transistor T3 and T4 will be SK100 and BEL AD149.
PARTS LIST OF SOUND OPEARTED RELAY
Resistor (all ¼-watt, ± 5% Carbon)
R1 = 47 kΩ
R2 = 5.6 KΩ
R3, R6 = 3.3 KΩ
R4 = 820 Ω
R5 = 15 KΩ
R7 = 220 Ω
R8 = 4.7 KΩ
VR1 = 250 Ω
|C1, C3 = 10 µF/12VC2 = 33 µF/12V|
|T1, T2 = AC126T3 = BC158 or SK100
T4 = AC128 or AD149
D1 = OA85
|X1 = Audio transformer or an eliminator transformerLS1 = 8Ω loudspeaker
B1 = 6V Lamp
M = Motor