Patent ID: 7161359

Claim:
A paper dispenser comprising: a housing having an inner chamber adapted to support a roll of paper and having a dispensing aperture; a motor adapted to dispense paper from the roll of paper through the dispensing aperture; and a proximity detection circuit for detecting the presence of a moving hand in the vicinity of said dispensing aperture, said circuit comprising: an antenna with which is associated a fixed time constant determined by a predetermined capacitance and a predetermined resistance, as well as a variable time constant that is longer than the fixed time constant by an amount determined by an external capacitive load, said variable time constant being on the order of twice said fixed time constant when the external capacitive load is a hand of a person in proximity to the antenna; an oscillator circuit for charging the antenna with an oscillating signal with a periodicity greater than said fixed time constant; an operational amplifier being operated as a unity gain follower and receiving an antenna signal from the antenna, the antenna signal being representative of an external capacitive load on the antenna and having a periodic exponential waveform that has a longer time constant and a lower amplitude when said external capacitive load is in proximity to said antenna, the waveform of the antenna signal being thus representative of changes in the external capacitive load on the antenna; a detector circuit electrically coupled to the operational amplifier for detecting changes in a low frequency component of the antenna signal and for generating a detection signal in response thereto; and a comparator responsive to the detection signal for generating an output signal to said motor when the detection signal is representative of a waving hand in proximity to the antenna.