Car Headlight Control

023 CAR HEADLIGHT CONTROL It is an annoying fact that you normally only realize that you have left your car headlights on when you want to restart the car only to find that the battery is flat. One of the possible ways of preventing this happening is offered by the present control. The circuit does not provide a warning but an action: when you switch off the ignition, relay Rel is de-energized and the headlights are switched off, unless you deliberately decide other- wise. That decision is made possible by switch Si, which, when operated, triggers silicon-controlled rectifier Thl so that Rel is energized. Note that this is possible only when the ignition switch, S2, is off, otherwise the voltage across Thl is so low, owing to shunt diode D1, that it can not be triggered. Since, 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 may then well be omitted altogether. Relay Rel should be a stand...