Example Relay Timer Circuit
One of the most commonly used circuits is that of the 555 Timer I.C.
The circuit is designed to turn the relay on and hold it ON for one second after seeing a positive going input.
Each time the windscreen washers are turned on, the circuit receives a 12 volt input.
The coupling capacitor, C4, requires a certain amount of time to discharge after seeing an input. So the relay can not be operated again by the headlamp washer switch until a short time has elapsed. This system removes the possibility of having the relay continually clacking on/off as the windscreen washer switch is operated.
The circuit has other uses, too.
Note that not all "555" timer I.C.s will operate satisfactorily in this circuit. The TLC555CP is recommended.
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