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CAR_HEADLIGHT_CONTROL

2017-01-17 14:13  
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CAR_HEADLIGHT_CONTROL
It is annoying to realize that you have left your car headlights on only to find that the battery is flat.One possible way to prevent this is with the present control. The circuit does not provide a warning, but an action: when you switch off the ignition, relay Re1 is de-energized and the headlights are switched off-unless you deliberately decide otherwise. That decision is made possible by switch S1, which, when operated, triggers silicon-controlled rectifier Th1 so that Re1 is nergized. Notice that this is possible only when the ignition switch, S2, is off. Otherwise, the voltage across Th1 is so low, owing to shunt diode Dl, that it cannot be triggered. However, the headlights should not normally be switched on when the ignition is off; in most cases S1 will be used only rarely and the switch can then be omitted altogether. The relay should be a stan-dard 12-V car type with contacts that can switch up to 25 A.