Light/Dark Detector


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This handy little circuit can tell the difference between darkness and light, making it very useful for switching on and off signs, porch lights or other things when it gets dark or light.

Schematic

Schematic for Light/Dark Detector

Parts

Part
Total Qty.
Description
Substitutions
R11100K Pot
Q112N3904 NPN Transistor2N2222
Q21NPN Phototransistor
RELAY19V Relay
MISC1Board, Wire, 9V Battery Snap (if battery used), Knob For R1

Notes

  1. R1 Adjusts sensitivity

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Comments

vinaya kumar
Light/Dark Detector
Monday, May 05, 2008 6:14:10 AM
can any give me the schematic for controlling the dim and dipping of the headlamps of the vehicle when it detects the vehicle coming in the opposite direction to it.. so as to make the people see the roads properly during night..
anonymoussai kiran
Light/Dark Detector
Friday, May 02, 2008 6:27:37 AM
i want to start this one but reading above comments it's not good to start i think for any one is it works if mail me plzzzzzzzzzzzzzzzz
anonymous
Light/Dark Detector
Tuesday, April 08, 2008 10:45:23 PM
Your circuits are totally crap, you need major adjustments, I see that theory is a completely ignored subject here. Not to mention that in the real world this circuit alone would fail, and electronics 101 you need a diode to take back voltage as the coil discharges, duh! Using the Diode toward the VCC end will not allow the coil to discharge fast this will prevent the back voltage.

(Editor's notes: I've been using this circuit for over 20 years to switch an EXIT sign on and off. But yes, I agree it should have a flyback diode.)

ROFL
Light/Dark Detector
Tuesday, April 08, 2008 10:55:11 AM
Nobody is going to make the circuit PCB for you, all your going to do is use it as your College Project. Do not build this circuit, it is poorly designed.
rohaan
Light/Dark Detector
Monday, April 07, 2008 9:43:32 AM
hey! did any of u work out this circuit..? i hv to do some thign like.. anyone wants to tell me bout.. and ya MuhaMMAD HASSAN what ur talking bout.. would u like to share? please help..its urgent!!! rohaanpathan_ekumeed@hotmail.com
Bande
Light/Dark Detector
Thursday, March 27, 2008 10:16:27 AM
Can u pls give me the god dam PCB of this god dam circuit... pls pls give it 2 me.i need that very badly. its a matter of life and death...
anonymous
Light/Dark Detector
Thursday, March 20, 2008 4:07:37 AM
i want to know can you protect your home with out using alarm
shaf
Light/Dark Detector
Monday, March 17, 2008 5:29:22 PM
can someone plz help me with light/dark detector by providing me a clear detail of how it works.for my AS level electronics course work i decided to design a security light which is going to place at the front door so when it is dark, it has to light up automatically as something moves, plz help, thanks.(karimmohammad108@hotmail.com).
SeanFalloy
Light/Dark Detector
Thursday, March 13, 2008 2:00:47 PM
Very Nice .. simple but usfull
shaf
Light/Dark Detector
Tuesday, March 11, 2008 2:43:13 PM
can someone please help me with clear explanation on how the light/dark detecter works, it would be very kind of you. it will really help with my school project, caz i am trying to design a security light as my year project, so this will be one of the sub system.
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