| 摘要 |
PURPOSE:To improve the reliability and to obtain the inexpensive circuit constitution of a videotelephone by making the setting of the current value of a constant-current circuit into non-adjusting when a power source is supplied from an indoor master equipment to an entrance slave equipment through a cable. CONSTITUTION:A television monitor 3 built in an indoor master equipment 4 and the television camera 5 of an entrance slave equipment 2 are connected with a coaxial cable 18 which transfers a picture and supplies the power source. And a video monitor control circuit built in the indoor master equipment 4 operates by detecting a voltage change that is recognized as the line level change when calling in a call line 13 and the output makes a constant-current circuit 16 which settles a line current and a switching circuit 17 for a television monitor on and the power source is supplied to the television camera 5 and the television monitor 3 for a prescribed time. Hereupon, a current value detecting element which sets up a current value according to an operation when a camera is pre-heated is used as the constant-current circuit 16 and a constant-current control is performed comparing this voltage effect with a reference voltage.
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