[Koil_1] knows he’s forgetful. In order to save himself from any undue harm, or possibly to keep from burning his house down, he felt he needed a timed power switch to run his soldering iron … ...

This is a very simple touch sensor switch that is build with the 555 timer IC. You just need to touch the metal plate and the relay gets energised and is kept in this state for about 100 seconds, then ...

S1 can be a tilt-sensitive switch with mercury if that will be used as a kitchen clock. With the buzzer on the power consumption of the timer alarm will be around 10 mA. Timer Alarm circuit diagram ...

Wanting an auto-off circuit simple electronics, [Kyle] threw together this auto shutoff circuit. The basic idea behind the cirucuit is to use a microcontroller as a timer controlling two transistors.