Posted on Sep 14, 2012 11035
This circuit switches car headlights to the low beam state when it senses the lights of an on-coming car. The received light is very low level and highly directional, indicating the use of a lens with the detector. A relatively large amount of hysteresis is built into the circuit to prevent `flashing lights.`
Sensitivity is set by the 22 megohm resistor to about 0.5 ft. candle at the transistor (0.01 at the lens), while hysteresis is determined by the Rl, R2 resistor voltage divider, parallel to the D41K3 collector emitter, which drives the 22 megohm resistor; maximum switching rate is limited by the 0.1 ?Â¥ capacitor to 15/minute. relay: 12v, 0.3a coil: 20a, form c. contacts or solid-state switching of 16a steady-state 160a cold filament surge. rating. lens; minimum 1" diameter. positioned for about 10? view angle.