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 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.