This is also known as Sun up alarm, in this circuit you can set the LDR’s sensitivity by 100k potentiometer, you can set it with any lamp around your room (tube light, bulb, LED etc) by varrying the 100k potentiometer. We can also control the buzzer time by 1M potentiometer 
 
You can Enhance this project and set the sensitivity of the LDR with a lazer light and keep it on the way of any door circuit at one side and lazer at other side of the door and a then you can make this project to buzz as soon as some one enters in a room 


I personally set this project in my room with sensitivity of tube light and whenever i came in and turn my room’s tube light on

sourced by: rookieelectronics

Parts Required:
  1. 100k & 1M potentiometers 
  2. 10k, 1Mx(3), 47k
  3. 0.1mF, 0.01mF & 10mF
  4. LDR
  5. BC337 transistor
  6. Beeper/Buzzer
  7. 9v Battery Supply
   Circuit Diagram:
 
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