Simple Electronic Touch Operated Switch Circuit Explained

Normally we come across switches which are mechanical in design and involve a spring loaded mechanism for the operations of producing ON/OFF of an electrical load. Such switches arte definitely good but not as modern and efficient as a touch switch would be. A simple circuit explaining the above high grade switching system is included here, which can be used as small modules for operating different electrical loads. Let's see how the circuit functions.,

An n-channel field effect transistor is

the basis of this simple touch operated switch.In its

quiescent state the voltage at the out-

put is about 3V. When the plate


briefly touched with a finger, the

minute currents between the body and

me plate alter the electric field at the

gate of the transistor. The effect is `to

cause a drop in output voltage. lt falls

almost to zero and can be used to

trigger a TTL flip—flop. This can be


in the usual way, using

two NAND gates from a 7400 IC. lf

several triggering circuits are required,

it is more convenient to use the 74118

sextuple bistable latch.

The value of the capacitor is not

critical, but 10uF is convenient. The

touch-plate can be an area of copper

etched on a circuit board, a square of

aluminium foil, or simply a drawing

pin pressed into an insulating support.

Courtesy: ETI Circuits

Article Written By Swagatam

Swagatam is a blogger at

Last updated on 25-07-2016 186 0

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