Here is the circuit diagram of touch switch circuit using timer IC NE 555. As the name says this circuit is based on NE 555 IC. This circuit is a simple touch plate controller which when touched on the touch plate operates the relay for a preset time then turns off automatically. This circuit has got applications in common equipments like touch operated doorbells, toys, buzzers etc.
The trigger pin of NE 555 has high input impedance. This property is exploited in this circuit in such a way that human body induced voltage is used for triggering this IC. When this IC is triggered, its output goes to high for a time duration determined by resistor R1 and capacitor C1. The relay used here is driven by a transistor. This relay contact is utilized here to drive loads like bell, lights, motor etc.
- Use a good quality PCB or common board to assemble this circuit.
- Use an IC holder for mounting the IC NE 555.
- Cut a 1 square cm thin metal sheet to make the touch plate.
- To setup the circuit connect to power supply and adjust R1 while keeping touching on the touch plate and stop at the point where relay activates.