MAINS-OPERATED touch switches for light dimmers and table lamps are not new but up till now they have all involved a metal plate or exposed metal work which you need to touch to operate. This Proximity Switch circuit is different – there is no exposed metal plate; you just wave your hand near a concealed plate and hand capacitance does the rest, turning the circuit on and off.

In practice the circuit is built into a small plastic case in series with the mains cord to the lamp. Alternatively, if the lamp base has space inside and is not made of metal, you could build the Proximity Switch right inside it.

Before we go any further, this circuit design is not suit-able for permanent installation as a light switch in your house wiring. This is because it is a 4-wire circuit and a light switch is normally a 2-wire circuit.

So how do you produce a Proximity Switch for 240VAC lights? It has been made possible by a new IC which is designed to work with a proximity sensor. The sensor is located behind the light switch pad, fully protected by a dielectric (ie, insulating) barrier. Thus the unit offers increased safety.

The sensor works on a principle of "charge transfer sensing", which has its origins back in the 1700s, when investigations where first being made into electricity. A study of this was made by Mr William Watson in England and also by the renowned Benjamin Franklin.

WARNING!! All parts in this circuit (including the sensor plate) operate at mains potential (ie, 240VAC) and must be fully isolated from the user. Do not operate this device unless it is fully enclosed in a plastic case. Similarly, do not work on the circuit or touch ANY part (sensor plate included) while it is plugged into a mains outlet. We recommend that only experienced people build this design.