| 摘要 |
An automatic switch is provided which includes a motion detector, a filter and amplifier circuit, a direction discrimination circuit and a processing circuit for controlling electrical load such as lights or home appliances in a room. The motion detector employs a pyroelectric infra-red detector for detecting the number of persons entering and leaving the room. The detector sends signals with phase differences to the processing circuit for counting. When the number of persons entering the room is greater than that of the number of persons leaving the room, the processing circuit automatically turns the lights on. Opposingly, when the number of persons entering the room is less than the number of persons leaving the room, the processing circuit turns the lights off.
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