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Automatic Headlight Brightness Switch

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Home > Circuits > Auto > Automatic Headlight Brightness Switch

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Driving the highway with your high-beam headlights can really increase your visibility, but can be a blinding hazard for other drivers. This simple circuit can be wired into your headlight switch to provide automatic switching between high and low beam headlights when there is oncoming traffic. It does this by sensing the lights of that traffic. In this way, you can drive safely with your high-beams on without blinding other drivers.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 5K 1/4W Resistor R2, R3, R4 3 5K Pot Q1 1 NPN Phototransistor Q2 1 2N3906 PNP Transistor K1 1 Low Current 12V SPST Relay K2 1 High Current 12V SPDT Relay S1 1 SPST Switch B1 1 Car Battery MISC 1 Case, wire, board, knobs for pots

Notes

1. Q1 should me mounted in such a way so it points toward the front of the car with a clear line of site. Suitable places are on the dashboard, in the front grill, etc.
2. Adjust all the pots for proper response by testing on a deserted road.
3. S1 enables and disables the circuit.
4. B1 is, obviously, in the car already.
5. Before you try to connect this circuit, get a wiring diagram for your car. Some auto manufacturers do weird things with wiring.
6. Connection A goes to the high beam circuit, B goes to the headlight switch common and C connects to the low beam circuit.

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Comments

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Timothy	Automatic Headlight Brightness Switch	Friday, February 19, 2010 1:10:54 PM
Where do A, B & C connect, how are they attached to the circuit and where in the car exactly is the circuit connected? Please send me the reply on my emial address. Please also send me the details of how the cicuit works its analysis. I would like to use for my project becuase it is so good. Thanks a banch. God Bless You
Stijn	Automatic Headlight Brightness Switch	Thursday, January 21, 2010 3:25:06 PM
Does this really work? I do not believe it will. Usually I switch my high-beam headlight off when I see someone coming from +- 400 meters. This tiny phototransistor will never detect the oncoming headlights over the street lanterns.
evi	Automatic Headlight Brightness Switch	Wednesday, December 23, 2009 5:45:51 PM
Hi!! I'm a student and this circuit is my hole project!!! Oh yes!!! Can you please, if that is possible, the analysis of it, the diagram, the function etc. Please!!! That would be very helpful for me 'cause I cannot find anything else elsewhere :/
mpouxesas	Automatic Headlight Brightness Switch	Sunday, November 29, 2009 11:20:41 AM
hi man,this is really a great job..bravo i want to design it on a PCB where i can find it??thx
garv	Automatic Headlight Brightness Switch	Tuesday, July 07, 2009 8:07:29 AM
Can we use this ckt to bike ?
Gaurav	Automatic Headlight Brightness Switch	Saturday, April 11, 2009 8:30:49 AM
hi frnd! this is really a great job............... but i have few problems as i want to design it on a PCB. so if possible can u get me the PCB layout of this circuit. also a explanatory description of this whole circuit. also how it works and where it should be attached in the vehichle........ i will be very thankful to u............
RAJ	Automatic Headlight Brightness Switch	Thursday, January 15, 2009 7:35:32 AM
Hey man this circuit is jus great. Particularly in India such circuits need to be implemented in the vehicles at the time of manufacturing itself because many of the people don't even understand the risk of driving with high-beam even when not neccesary. Good work man.
anonymous	Automatic Headlight Brightness Switch	Friday, December 12, 2008 11:39:02 AM
Why did omit the back emf diode from the relay coil?
garv	Automatic Headlight Brightness Switch	Wednesday, September 17, 2008 9:22:59 AM
hi bro good 1 i'm facing big problem while driving at night as u know the problem with HeroHonda CBZ* it's headlight power is very low I din't get what is k1& kt please sent me this circuit in detail thanks garv
mani	Automatic Headlight Brightness Switch	Saturday, August 16, 2008 4:23:04 PM
this circuit is of great use to the persons who drive but even don't know about flash on road as it is imp. tool of driver to drive properlly and to persons do not know about high and low beam usage which is great cause ofaccident in night