Dark Sensitive Switch

Rajkumar Sharma      http://www.rajkumarsharma.com  
Project 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






7 Response on “Dark Sensitive Switch

  1. 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.



    1. 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.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.