A delayed headlight control for a car allows one to illuminate the path on roads, and driveways, where there is no lighting. Also sometimes called a “Relay Delay”, it keeps the headlights switched ON for a pre-set amount of time after switching OFF the ignition.
It is a very useful safety device if your driveway has no lights and you need to illuminate it until you are indoors. I was asked my personnel manager to build and install it, as she was not very happy having to park the car on an empty long road during the dark winter evenings.
Although many modern cars have such a facility, many cars do not, and retro fitting a delay circuit like this is very basic electronic engineering. A headlight delay tends to work well with classic and older cars where access to the wiring is possible.
People often think that you forgot to turn OFF your headlights; however, the headlights and the associated circuit automatically switch OFF after a delay of 50 seconds.
The 555 timer IC operates directly on 12 V car batteries, and draws a negligible amount of current making it very efficient.
When the ignition switch is to the ON position, current to the relay coil arrives via Diode D3 and the contacts RLA/1 close, providing power to both headlights and the timer circuit. Hence, when the ignition is ON the headlights operate as they normally would.
Relay Delay – 50 Seconds
When the ignition switch is to the OFF position, there is no longer any current to the relay coil via D3, and simultaneously C2 provides a negative going trigger pulse to pin 2, initiating a 50 second delay cycle, during which time the relay coil is energised via D2 and the relay contacts RLA/1 remain closed.
After 50 seconds, the power to the relay coil discontinues and the contacts RLA/1 open cutting power to the whole circuit including the headlights and the timer IC itself.