This timer circuit is activated by Power On. Here are two of the simplest circuits you can build with a 555 timer and just one or 2 resistors and one or 2 capacitors. The output turns on INSTANTLY at power up and turns off at the end of the desired time. It is a one shot, monostable multivibrator cofiguration. What is particularly unique is there is no momentary contact pushbutton switch. The output is immediately on when power is applied. Activating a pushbutton switch is not required.

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