Simple light-switch circuit

Posted on Mar 8, 2013

The circuit is a light switch who triggers when light drops on photo resistor. It is fairly simple in construction and can be used in a million applications. The photoresistor and the trimmer work as a voltage divider and also polarize the transistor TR1. TR1 triggers TR2 and TR2 drives the relay. Trimmer R7 is for adjusting the sensitivity of the circuit.

Simple light-switch circuit - image 1
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Parts: R = photoresistor R1= 4.7 Kohm R2= 1.2 Kohm R3= 2.2 Kohm R4= 1.2 Kohm R5= 1.2 Kohm R6= 2.7 Kohm R7= 100Kohm Trimmer C1 = 10uf/16V electrolytic TR1= BC107 - BC108 NPN TR2= BC107 - BC108 NPN TR3= BC557 - BC558 PNP - BC327 D1 = 1N4148 Relay = any 12Volt relay

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