Body Detector
Approx construction cost US$36
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. Capacitance is also one of a vast range of physical phenomena that may be translated into electrical oscillations.
The Body Detector featured in this article relies on the fact that the 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 a human body.
In this project, a metal sensor is attached to the positive plate of the small 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.
More details on this construction project can be found in the March 2001 issue of EPE Online, the world's first web-delivered electronics and computing hobbyist magazine.
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