Abstract:
This project make use of an LDR (light dependent resistor) to sense light and darkness and control the bright white LED.
Circuit diagram
Short Description
- 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.
Material list
| Sr. No. | Component | Specifications | Quantity | |
| 1 | IC LM 324 | standard IC | 1 | |
| 2 | resistor | 10k,0.25W | 2 | |
| 3 | resistor | 2k2,0.25W | 1 | |
| 4 | preset | 5k,top screw settable,blue | 1 | |
| 5 | LED | bright white, 5mm | 1 | |
| 6 | LDR | standard | 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.
विज्ञान केंद्र 