Light dependent resistor digital control circuit

Details Light dependent resistor digital control circuit Light dependent resistor digital control circuit

1989-03-17

1990-01-16

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

250221, H01J 4014

Patent

active

048945277

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.

REFERENCES:
patent: 4514727 (1985-04-01), Van Antwerp
patent: 4644149 (1987-02-01), Tsunekawa
patent: 4768020 (1988-08-01), Chen
patent: 4847486 (1989-07-01), Moran et al.

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