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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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

Steve Automatic Headlight Brightness Switch Thursday, January 24, 2008 5:05:27 AM

Guten tag.I am germany student, I like your circuit yes, if you email please me information how it work. i do this for school and i like cars, sexytime please danke kiss kiss

dhanu Automatic Headlight Brightness Switch Wednesday, January 23, 2008 9:35:23 AM

i really like this project ... could i know about the detail descriptions of the circuit and the cost of this project???????? thank uuuuuu...

Zeberdy Automatic Headlight Brightness Switch Thursday, January 17, 2008 9:26:16 AM

Yooo dis is well elpful i is gunna use it az me projec if youse can gis some more info like i wud much appreciate it aite. much loves. keep it reals Zebby xxooxx

jon dom Automatic Headlight Brightness Switch Thursday, January 10, 2008 8:56:25 AM

aaaaaaaaaaaaaye mate! kin waaaaaaaa this project is mint like it'd be reeet sound if ya could let me knows about some more info like i iz doing it for me project its sound! cannie wait kid hit me back inabit mert(Y)

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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
Steve	Automatic Headlight Brightness Switch	Thursday, January 24, 2008 5:05:27 AM
Guten tag.I am germany student, I like your circuit yes, if you email please me information how it work. i do this for school and i like cars, sexytime please danke kiss kiss
dhanu	Automatic Headlight Brightness Switch	Wednesday, January 23, 2008 9:35:23 AM
i really like this project ... could i know about the detail descriptions of the circuit and the cost of this project???????? thank uuuuuu...
Zeberdy	Automatic Headlight Brightness Switch	Thursday, January 17, 2008 9:26:16 AM
Yooo dis is well elpful i is gunna use it az me projec if youse can gis some more info like i wud much appreciate it aite. much loves. keep it reals Zebby xxooxx
jon dom	Automatic Headlight Brightness Switch	Thursday, January 10, 2008 8:56:25 AM
aaaaaaaaaaaaaye mate! kin waaaaaaaa this project is mint like it'd be reeet sound if ya could let me knows about some more info like i iz doing it for me project its sound! cannie wait kid hit me back inabit mert(Y)