Often,we find that a lot of motorist.They have forgotten to turn on light in a car when parking.then back to start the machine,it did not work,because a battery did not have a energy. but this circuit will be warning a car driver for instantly know,when we forget to open the car door or forgetting to turn off lights in the car.
From this circuit picture,The transistor Q1 and Q2 are working to astable multivibrator circuit.The collector pin of the Q2 used a loudspeaker was a load’s circuit.The capacitors C1, C2 and a resistors R3, R4 was timing part’s circuit, and to set a frequency of output signal,
When turn on switch,then the current a flow to pass a diode D1 and a resistor R1. It were positive power supply’s this circuit,then the ZD1 6.2v zener diode use to voltage regulated at 9.1 volt of the power supply.
The ground wire is connected to the switch, cabin light, which is controlled by the door.The circuit is connected to ground only, when the door is opened only.
The ocean, off the switch to start and turn left. Then the driver opened the door enough. The Oscillator generator circuit will alarm,that forgot turn off the light.