Touch Switch Circuit using NE 555
This is the circuit diagram of a small touch plate controller using IC NE 555 .This circuit is ideally useful for making touch operated doorbells, buzzers,toys etc which when touched on the touch plate operates the relay for a preset time and the turns off automatically.
This circuit is realized by utilizing the high input impedance of trigger pin of the 555 IC.When the IC is triggered by the induced voltage of human body the output goes high for a time determined by R1 and C1.The transistor is used to drive the relay.The relay contacts can be used to drive the load like bell, motor , lights etc.
To make the touch plate cut a 1 square cm thin metal sheet.
To setup the circuit connect to power supply and adjust R1 while keeping touching on the touch plate.Stop at the point where relay activates.If relay is in the activated state initially then do the same until the relay is deactivated.