| 摘要 |
PURPOSE:To detect the visit of a visitor without requiring an interphone switch or a sensor or the like by intermittently operating only an image pickup part, detecting a level difference between intermittently fed video signals, and driving an image receiving part when the detected value goes above a set value. CONSTITUTION:A timing circuit 7 intermittently operates an image pickup element 2 and an LED 9 at a short time interval and alternately opens and closes gate circuits 10, 11 at a short time interval. The video signals inputted through the gate circuits 10, 11 are respectively integrated and averaged in integrating circuits 13, 14 and the level value of the brightness is held in sample hold circuits 15, 16. When the visitor 6 comes, since the level difference is generated in the brightness between the video signals in the vicinity of the visitor 6, the difference between the holding values of the sample hold circuits 15, 16 is enlarged, the arithmetic value of a differential amplifier 17 becomes larger than the set value of a setting part 19, an output appears in the output side of a comparator 18, a driving control circuit 8 supplies a power to the image receiving part 5, sets the timing circuit 7 to a long time interval and the image receiving part 5 displays the visitor 6.
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