Introduction: Car Light Switch Circuit

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This circuit may be used to automatically switch off an interior car light, with a time delay of 15 seconds or 3 minutes.
The light is controlled by a manual and a door switch.
By activating the manual switch or opening the door Q2 turns on for an instant in order to lead the output to the high level: the light goes on.  If the manual switch is activated or the door is open Q3 keeps on and the current flows through C3: the light backs off after 3 minutes.
By closing the door Q3 and Q5 switch off, while Q4 switches on. So the current flows through C1 and the light backs off after 15 seconds.
By deactivating the manual switch Q4 turns on after an instant (due to Q6), then the light backs off with no delay.