Easier Approach to Electronic Projects

Simple Light Sensor using 741 Op-amp

This is a Light sensor circuit. Probably most simple and interesting circuit to play with. It can be configured as either shadow detector or Light detector, which means it can detect the intensity of light.

Right now in the circuit diagram it is configured as a Shadow Detector, that means the LED will turn on when we show a bright light over LDR.

We can change this circuit as Light Detector by simply swapping the pins 2 & 3 of 741 Comparator IC, and then LED will turn on when LDR is dark.

In this circuit, please make sure that pins no 1,5 & 8 are not connected and left idle.

Pin 6 is output pin. In the circuit it is connected to an LED via 1K resistor, but you can also connect a transistor to turn on a relay, motor or any other output.


Parts Required & Circuit Diagram:

  1. 10k potentiometer, 10k & 1k
  2. LDR
  3. 741 Comparator op-amp
  4. LED
  5. 9V battery



Bread board Arrangement:


Strip Board version:

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