| 摘要 |
PURPOSE:To simplify the configuration of circuit and to reduce the cost by detecting the line level at the time of call of call line and supplying the power to TV camera and TV monitor for a prescribed time and shutting off the power supply at the end of the call of the call line. CONSTITUTION:A call detecting circuit 17 detects the change of voltage as the line change at the time of call of call line 27, and turns on lightening lamp switching circuit 29, constant current circuit 30 which keeps the line current constant, TV monitor switching circuit 31, and supplies the power to an illumination lamp 23, TV camera 31 and TV monitor 14 for a prescribed time. Call-over detection circuit 19 detects the voltage change as the line level change at the time of the end of call and turns off the illumination lamp switching circuit 29, constant current circuit 30, and TV monitor switching circuit 31, and stops the power supply to the illumination lamp 23, TV camera 11 and TV monitor 14.
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