Interface LDR Sensor With PIC


A Light Dependent Resistor(LDR) or a photoresistor is a non-linear device whose resistivity is a function of the incident electromagnetic radiation.

  • A light-dependent resistor works on the principle of photoconductivity.
  • Photoconductivity is an optical phenomenon in which the conductivity of the material (Hence resistivity) reduces when light is absorbed by the material.
  • When light falls the resistance of the device has decreased.
  • When the light-dependent resistor is kept in dark, its resistance is very high. This resistance is called as dark resistance.
  • It has high as 1012 ohm when LDR kept in dark.
  • When the light is incident on a photocell it usually takes about 8 to 12ms for the change in resistance to take place.
  • While it takes seconds for the resistance to rise back again to its initial value after removal of light.


  • Weather Monitoring System.
  • Manufacturing Industry.

Hardware Required

  • LDR.
  • ADC 0804.
  • PIC16f877a MicroController.