Light dependent resistor digital control circuit
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United States of America Patent
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-
Jan 16, 1990
Grant Date -
N/A
app pub date -
Mar 17, 1989
filing date -
Mar 17, 1989
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A digitally controlled ambient light detection circuit for an infrared intrusion detector. A light dependent resistor is used as a charging circuit for pulse driven capacitor on the input of a digital buffer circuit so that the time of reaching the threshold voltage of the buffer varys with the light falling on the light dependent resistor. The buffer output is then compared to a reference pulse which is synchronized with, but delayed from, the capacitor charging pulse. If the buffer output occurs after the reference pulse it indicates low light, and an output signal is generated to activate the infrared intrusion detector.
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