19-08-2011, 11:30 AM
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The circuit is designed to switch your car's lights from its high beams to its low beams when traffic approaches. With Q1 in moderate darkness, the variable resistors should be adjusted to produce no base current through Q2. When there are no approaching headlights to trigger the system, K1 is not energized, and its contacts remain closed. Relay K2 is energized, and the high-beam lights are on.
When light from an approaching car shines on the phototransistor, the base current and collector current of the PNP transistor increase substantially, and K1 is energized. That automatically deenergizes K2 (a power-type relay fed directly by the car battery), shutting off the high-beam headlights and tuming on the low-beam lamps. Switch S1 should be conveniently located on the dash of the vehicle. Keep the switch turned off during the day so that the circuit will not leave your lights on in sunlight.
The circuit is designed to switch your car's lights from its high beams to its low beams when traffic approaches. With Q1 in moderate darkness, the variable resistors should be adjusted to produce no base current through Q2. When there are no approaching headlights to trigger the system, K1 is not energized, and its contacts remain closed. Relay K2 is energized, and the high-beam lights are on.
When light from an approaching car shines on the phototransistor, the base current and collector current of the PNP transistor increase substantially, and K1 is energized. That automatically deenergizes K2 (a power-type relay fed directly by the car battery), shutting off the high-beam headlights and tuming on the low-beam lamps. Switch S1 should be conveniently located on the dash of the vehicle. Keep the switch turned off during the day so that the circuit will not leave your lights on in sunlight.
