Optical motion sensor
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United States of America Patent
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-
Apr 5, 1988
Grant Date -
N/A
app pub date -
Feb 2, 1987
filing date -
Feb 2, 1987
priority date (Note) -
Expired
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Abstract
An optical motion sensor comprises first and second light emitting diodes that emit complementary pulsed beams of infrared energy within a sensing region. A photodiode sums the energies to produce a proportional sensing signal. An amplifier AC coupled to the photodiode blocks the constant portion of the sensing signal and passes a time varying signal portion produced by motion of an object to a sampling circuit. The sampling circuit samples the sensing signal synchronous with emission of the first pulsed beam and converts the time varying signal to a proportional detection signal. An integrator coupled to the sampling circuit responds to a detection signal by modulating the intensity of the second pulsed beam to null the earlier time varying portion of the sensing signal. The motion sensor can be configured as a presence sensor by changing the time constant of the integrator. A slower time constant changes the rate at which the beam intensity is modulated and thus increases the duration of the detection signal.
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