INTRUDER DETECTION SYSTEM UTILIZING ARTIFICIAL AMBIENT LIGHT

摘要

The detection system includes a pair of photocells connected in series to form a voltage divider. One photocell is responsive to ambient light (supplied by either an incandescent or fluorescent lamp) and the other to reference light (supplied by a small auxiliary incandescent lamp). Inasmuch as the system is responsive to artificial ambient light, which contains an alternating component by reason of being supplied by the usual 60 hertz power source, any spurious changes in the supply voltage are nullified by the voltage divider since my detection system is also connected to the same source as that supplying the artificial ambient light. The signal forwarded from the voltage divider comprising the two photocells is filtered, amplified, rectified, and the resulting output signal employed to actuate a suitable alarm, this being when an intruder has caused a change in the amount of artificial light impinging upon the photocell responsive to ambient light. The system is insensitive to changes in ambient light derived from sources other than the alternating current power supply, such as changes in daylight or headlights on passing automobiles.