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

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.

Adjust all the pots for proper response by testing on a deserted road.

S1 enables and disables the circuit.

B1 is, obviously, in the car already.

Before you try to connect this circuit, get a wiring diagram for your car. Some auto manufacturers do weird things with wiring.

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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shiva Automatic Headlight Brightness Switch Wednesday, September 17, 2014 9:49:10 AM

Good concept ...I want this one as my project please help me to implement this one and please give information about this like block diagram,specification and all

venki Automatic Headlight Brightness Switch Thursday, October 24, 2013 1:20:33 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 email address. Please also send me the details of how the circuit works its analysis. I would like to use for my project because it is so nice.

reza Automatic Headlight Brightness Switch Tuesday, April 09, 2013 3:03:18 AM

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!!!!!!!!1

anonymous Automatic Headlight Brightness Switch Monday, July 09, 2012 6:48:10 PM

Do the work yourself, Lukas

Lukas 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 :/ Wednesday, May 30, 2012 10:23:26 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 :/

sarun Automatic Headlight Brightness Switch Sunday, August 07, 2011 6:24:05 AM

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!!!!!!!!1

ndayisenga jean claude Automatic Headlight Brightness Switch Sunday, January 23, 2011 3:22:18 PM

hey man this circuit is so great .i wanna know how and where we connect this in the car ,if is possible show me a picture of car connected with this circuit thinks i like them!!!!!!!!!!!!

Weedo Automatic Headlight Brightness Switch Sunday, September 19, 2010 7:20:20 AM

photodiode would make a better in this circuit, cheaper, and easier. Stijn... yeah sure you switch them off +- 400 but did ya know that you can see the oncoming cars high beam like 600+m, photo diode senses this beam (if propelly mounted) like 1-2,5Km from u.

Cesar Automatic Headlight Brightness Switch Thursday, June 03, 2010 10:40:35 AM

Adjusting the pots R3 and R4 to the minimun will create a short to the battery terminals, did you notice that? How can be this problem fixed? Thanks

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

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shiva	Automatic Headlight Brightness Switch	Wednesday, September 17, 2014 9:49:10 AM
Good concept ...I want this one as my project please help me to implement this one and please give information about this like block diagram,specification and all
venki	Automatic Headlight Brightness Switch	Thursday, October 24, 2013 1:20:33 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 email address. Please also send me the details of how the circuit works its analysis. I would like to use for my project because it is so nice.
reza	Automatic Headlight Brightness Switch	Tuesday, April 09, 2013 3:03:18 AM
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!!!!!!!!1
anonymous	Automatic Headlight Brightness Switch	Monday, July 09, 2012 6:48:10 PM
Do the work yourself, Lukas
Lukas	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 :/	Wednesday, May 30, 2012 10:23:26 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 :/
sarun	Automatic Headlight Brightness Switch	Sunday, August 07, 2011 6:24:05 AM
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!!!!!!!!1
ndayisenga jean claude	Automatic Headlight Brightness Switch	Sunday, January 23, 2011 3:22:18 PM
hey man this circuit is so great .i wanna know how and where we connect this in the car ,if is possible show me a picture of car connected with this circuit thinks i like them!!!!!!!!!!!!
Weedo	Automatic Headlight Brightness Switch	Sunday, September 19, 2010 7:20:20 AM
photodiode would make a better in this circuit, cheaper, and easier. Stijn... yeah sure you switch them off +- 400 but did ya know that you can see the oncoming cars high beam like 600+m, photo diode senses this beam (if propelly mounted) like 1-2,5Km from u.
Cesar	Automatic Headlight Brightness Switch	Thursday, June 03, 2010 10:40:35 AM
Adjusting the pots R3 and R4 to the minimun will create a short to the battery terminals, did you notice that? How can be this problem fixed? Thanks
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