Importance

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Abstract

A proximity sensing device comprising a sensor including a planar capacitor (1) having a central region (1a) and an outer region (1b) separated by a dielectric area, differentiator means (2,3) associated with said capacitor to form a spiked output pulse from a drive input pulse having at least one stepped edge and comparitor means (10) to repeatedly compare said spiked output pulses with a reference datum indicative of no proximity body being located adjacent to or touching said sensor to determine if such a proximity body is so located. The ration of the perimeters of the central region and dielectric area of the planar capacitor is approximately 2:1 and its capacitance is comparable to that of a human finger.

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First Claim