Car Interior Light Delay

0 It"s dark and it"s raining cats and dogs. You rush to your car, open the door and quickly close it behind you again. Then you sit there fumbling for the ignition lock. Solution? Add the following cir- cuit, which will keep your car"s interior light on for a little while after the door is closed. The circuit is connected across the switch in the door post. These switches 14 SUPPLEMENT are removed quite easily. In the circuit diagram, Si is the switch in the car"s doorpost and Li is the interior light. As long as the door is open, Si is closed and the light is on. When the door is closed, Si opens and the light goes out. The full 12 V from the car bat- tery is then present across the switch. The circuit detects when the voltage across Si begins to rise. Transistor T3, and consequently T1 and T2, is then switched on. This results in the voltage across Si rising to about 1 V, after which it can increase only very slowly. This means that the interior light stays on, although its brig...