Many people forgets the bathroom and toilet lamps in ON state, absolutely this causes increasing electric bill and even decrease lamps lifespan. This circuit is a simple way to turning ON and OFF the bathroom or toilet lamp automatically without using microcontroller.
The circuit based on the counter IC4017 and laser. when a person go to bathroom his body cut the laser ray that is focused on the LDR in another side of the door frame, connecting and disconnecting the laser ray changed the LDR electric resistance and giving a positive signal to pin14 of the IC4017 through transistor 2N2222, since pin4 jumped to reset pin (pin15) so the output selector will be changed between pin3 and pin2. Pin3 run the transistor to running the relay.
Two LEDs showing ON state and OFF state. 330 ohm resistor used to LEDs protection by giving 15mA current to them.
You can use any other NPN transistor rather than 2N2222 such as BC547, C9013, 2N5551, etc.
This circuit is suitable for light switching for any place that used by one person such as toilet and bathroom, you can't use it for the room because when second person coming inside the room the lamp will be turns OFF.
Part list:
IC4017
Transistor 2N2222
Laser 5mW
Relay 5v
LEDs
LDR
Resistor 1K
Resistor 200K
Resistor 2.2K
Resistor 330R
Capacitor 10nF
Diode 1N4007
In following video you can watch how the circuit works:
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