Dark Sensitive Switch

  • Rajkumar Sharma
  • 13184
  • easy
  • Tested

photo (1)


Dark Sensitive switch project based on single BC547 transistor, Relay operates when light that falls on the LDR, goes below a set point. It’s very simple and low cost dark sensitive switch required few components.


  • Input : 12 VDC @ 55 mA
  •  Relay output : NC – C – NO
  •  Onboard preset to set the level
  •  Power-On LED indicator
  •  Relay On LED indicator
  •  Screw terminal connector for easy relay output connection
  •  Four mounting holes of 3.2 mm each
  •  PCB dimensions 44 mm x 40 mm







  • yuvaraj

    sir pls send me pcb layout image or layout work file

    5 years ago
  • Arun Verma

    Sir, I want to buy this circuit. Please tell how to pursue.

    5 years ago
  • nosert

    hi, what is the value LDR ? 100k, 500k or 1M ?

    4 years ago
    • Electronics Lab

      A 100k should work nice.

      4 years ago
  • Sunny Sharma

    i have the same circuit, i did connected the input 12v, LEDS are glowing fine, but i dont know the relay connections can you please help or any short video would be a great favour on my head.



    3 years ago
    • admin

      The relay acts as a mechanical switch. There are 3 pins available, a common pin and NO, NC pins. NO means “normal open”‘ and NC means “normal connected”. Depending on your application you can use 2 of these pins to form a switch that is closed or opened when the relay energizes.

      3 years ago

Leave a Reply



By continuing to use the site, you agree to the use of cookies. more info

The cookie settings on this website are set to "allow cookies" to give you the best browsing experience possible. If you continue to use this website without changing your cookie settings or you click "Accept" below then you are consenting to this.