1. 555 touch timer switch
The integrated circuit IC1 is a 555 timing circuit, which is connected here as a monostable circuit. Usually, because there is no induced voltage on the P terminal of the touch panel, the capacitor C1 is discharged through the 7th pin of 555, the output of the 3rd pin is low level, the relay KS is released, and the electric light is not lit.
When it is necessary to turn on the light, touch the metal piece P by hand, and the clutter signal voltage of 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, and the relay KS pulls in, the electric light point bright. At the same time, the 555 pin 7 is internally cut off, and the power supply charges C1 through R1. This is the beginning of timing.
When the voltage on the capacitor C1 rises to 2/3 of the power supply voltage, the 555 seventh foot channel causes C1 to discharge, so that the output of the third pin changes from the high level to the low level, the relay is released, the light is extinguished, and the timing ends.
The timing is determined by R1 and C1: T1=1.1R1*C1. According to the values indicated in the figure, the timing time is about 4 minutes. D1 can be used with 1N4148 or 1N4001.
2. Single power supply dual power supply circuit
In the circuit of the drawing, the time base circuit 555 is connected to an unsteady circuit, and the square pin has an output frequency of 20 kHz and a square wave with a duty ratio of 1:1. When pin 3 is high, C4 is charged; when low, C3 is charged. Due to the existence of VD1 and VD2, C3 and C4 are only charged and not discharged in the circuit. The maximum charging value is EC, and the B terminal is grounded. At both ends of A and C, the dual power supply of +/-EC is obtained. The output current of this circuit exceeds 50mA.