NE555 touch timer switch

Integrated circuit IC1 is a 555 timing circuit, which is connected as a monostable circuit here. Usually, since there is no induced voltage at the P end of the touch panel, the capacitor C1 is discharged through the 7th foot of the 555, the output of the 3rd foot is low level, the relay KS is released, and the light is off.

When you need to turn on the light, touch the metal sheet P with your hand. The voltage of the clutter signal induced by the human body is added from C2 to the trigger end of 555, so that the output of 555 changes from low to high level, the relay KS is closed, and the light is on. At the same time, the 7th foot of 555 is cut off internally, and the power supply charges C1 through R1, which is the beginning of the timing.
When the voltage on capacitor C1 rises to 2/3 of the power supply voltage, the 7th foot of 555 is turned on to discharge C1, so that the output of the 3rd foot changes from high level to low level, the relay is released, the light goes out, and the timing ends.
The timing length is determined by R1 and C1: T1=1.1R1*C1. According to the value marked in the figure, the timing time is about 4 minutes. D1 can choose 1N4148 or 1N4001.