Automatic DC light switch

Following circuit is an automatic DC light switch, it run the load in dark.
the load can be a lamp or any other device, works by 3 to 12 volts
It is possible to use this circuit as anti theft system if we connect a laser and an alarm,
so when opens the door, laser ray move from LDR and alarm be turn on.
T2 should be changed by any other power NPN transistor if the load consumed more than 100 mA.

Parts list:
Transistor BC547 (2pcs)
LDR
Resistor 100k
Resistor 1k

Note: if you want to use LED as load, so have to use protection resistor 200 ohm for 3v battery or 680 ohm for 12v battery.

Automatic DC light switch


Location: Iraq

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