Capacitive Sensors

Posted on Feb 6, 2014

For proper operation, circuit ground must be connected via a small value, high voltage-rating capacitor to one side of the mains supply socket. The `Live` side is the right one. The purpose of this circuit is to animate shop-windows by means of a capacitive sensor placed behind a post-card-like banner. The card is placed against the glass in

Capacitive Sensors
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side the shop-window, and the visitor can activate the relay placing his hand on the card, from the outside. Especially suited for toy-shops, the circuit can activate model trains, small electric racing cars, lights etc. Further applications are left at user`s imagination. Adopt it to increase the impact of your shop-window on next Christmas season! Q1, Q2 & Q3 form a high impedance super-Darlington that drives the relay, amplifying the 50Hz alternate mains-supply frequency induced in the sensor by the human body. C1 & D2, D3 ensure a clean relay`s switching. Power supply can be any commercial wall plug-in transformer with rectifier and smoothing capacitor, capable of supplying the voltage and current necessary to power the relay you intend to use.

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