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Friday, February 12, 2010

LIGHT ACTIVATED SWITCH CIRCUIT


  • This is the circuit diagram of a light activated switch based on National Semiconductors comparator IC LM 311 and a LDR.
  • The circuit is based on a voltage comparator circuit wired around IC 1.The non inverting in put of IC1 is given with a reference voltage of 6V using resistors R3 and R4.
  • Adjust POT R1 to set the desired light intensity for switching the relay.
  • For this illuminate the LDR with the desire intensity light.
  • The relay will be either on or off.Adjust POT R1 slowly so that the state of the relay changes.
  • That’s it.Now the circuit is set for the given intensity of light.
  • Assemble the circuit on a good quality PCB or common board.
  • You can use either a 12 V battery or a well regulated & filtered 12V DC mains operated power supply.
  • The pin 5&6 (Balance & Balance/Strobe ) of IC LM311 are shorted to minimize the chance of oscillations.
  • The pin out of LM311 is also given together with the circuit diagram
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