Body Detector

Create your own "invisible" protective shield and let the force be with you!

Capacitance is an extraordinary phenomenon in that it is able to work through empty space. This is a quality that is normally taken for granted. The accumulation of charge on a metal plate gives rise to an electric field, which will affect another plate in direct proportion on the inverse of is distance. Capacitance is also one of a vast range of physical phenomena that may be translated into electrical oscillations.

The Body Detector relies on the fact that human body itself possesses a fairly large order of capacitance to the ground (earth) and that if such a body approaches the positive plate of a given capacitor, its value will rise. If then, one could find a means to detect such an increase in capacitance, one would have an effective means of detecting the presence of human body.

In the presence application, a metal sensor is attached to the positive plate of timing capacitor of an RC oscillator, so that when a human body approaches, the value of C increases and the frequency of the RC oscillator decreases. This drop in frequency is detected digitally and is used to switch a relay.