Thursday, February 17, 2011

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NE555 simples Touch Switch

The 555 can be used to create a Touch Switch. The only problem with this is the 555 consumes about 8mA, at all times when the supply is connected. 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. See below for an ON-OFF touch switch using a 555.
 NE555  simples Touch Switch Circuit
NE555 Pinout
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.

Note: 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.

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