• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Resource icon

Dark Detector 2011-06-16

The dark detector circuit shown here can be used to produce an audible alarm when the light inside a room goes OFF. The circuit is build around timer IC NE555.A general purpose LDR is used for sensing the light. When proper light is falling on the LDR its resistance is very low. When there is no light the LDR resistance increases. At this time the IC is triggered and drives the buzzer to produce an alarm sound. If a transistor and relay is connected at the output (pin3) of IC1 instead of the buzzer, electrical appliances can be switched according to the light.

Schematic

dark-detector-_circuit.JPG

Notes

  • The LDR ,R4 can be any general purpose LDR.
  • The circuit must be assembled on a good quality PCB or common board.
  • The circuit can be powered from a 9V PP3 battery.
  • The POT,R3 can be sued as a volume controller.
  • Mount the IC1 on a holder.It will make replacements easy.
Author
3lectrix
First release
Last update
Rating
0.00 star(s) 0 ratings

More resources from 3lectrix

Latest threads

EE World Online Articles

Loading

 
Top