| 摘要 |
PURPOSE:To control a secrecy by providing a means which judges whether or not a telephone set or the like is used by a direction in which loop current are running, and a means which detects the loop currents at the telephone set or the like. CONSTITUTION:When the receiver of an automatic answering telephone set 8 is lifted up, the loop currents are running through speech lines 1a and 1b, the loop currents are detected by photocouplers 2 and 3, and a signal is transmitted to a CPU 10. A relay 7 is turned OFF at the time of realizing the secrecy of the telephone set 9, and turned ON at the time of releasing the secrecy and communicating by three people by the CPU 10. When the receiver of the telephone set 9 is first lifted up, the loop currents are detected by photocouplers 4 and 5, and a relay 6 is turned ON and OFF by the CPU 10 in order to control the secrecy. And also, when the secrecy of the telephone set 8 is released in the communication by a general telephone set 16, and the secrecy of a telephone set 9 is realized, the relay 6 is turned ON, and the relay 7 is turned OFF. Therefore, even when plural telephone sets are branch-connected, it is possible to always judge which telephone set is used. |
