This project make use of an LDR (light dependent resistor) to sense light and darkness and control the bright white LED.
- The circuit uses IC LM324 (quad op-amp).
- One of the four op-amps is used as a voltage comparator.
- When it is dark, resistance of LDR is high. Voltage across it is higher than the “preset voltage” at inverting terminal and op-amp output is high. (You can set the threshold of darkness by adjusting the inverting voltage).
- High op-amp output makes the bright white LED “ON“.
- If light intensity in the room is high, the voltage across LDR is low and is less than the inverting voltage. This makes the op-amp output “low”.
- This forces the LED not to glow.
- You can test the circuit simply by covering and un-covering the LDR by hand.
|1||IC LM 324||standard IC||1|
|4||preset||5k,top screw settable,blue||1|
|5||LED||bright white, 5mm||1|
|7||Battery||9v, flat, with snapper||1|
|8||PCB||general purpose, 4″X4″||1|
|9||Misc||solder metal, wire etc.|
This project is available in the kit form. Contact Omkar to buy it. This site has no commercial connection with his activities.