Automatic headlight brightness switch

Posted by Author makecircuits

Automatic headlight brightness switch

Driving the highway with your high-beam headlights can really increase your visibility, but can he a blinding hazard for other drivers. This simple circuit can be wired into your headlight switch to provide automatic switching betw1een 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.