| 摘要 |
PURPOSE:To reduce the size and weight of a device while maintaining high reliability by using a photocoupler for the DC loop of a line and a telephone set. CONSTITUTION:When the telephone set TEL is put in the off-hook state, the DC loop of L1 Cml1 TEL Cml2 diode D3 input part of photocoupler PC3 L2 is formed through the DC line of TEL to allow telephone service with an opponent subscriber. When the TEL is placed in the on-hook state, the level is suppressed by D1 and D2 to a constant voltage through C2 and R3 of a call signal detection part 2 and detected by PC1, whose output DC on-off signal is outputted through a waveform shaping circuit 4 as a call detection signal CI to a terminal 5. The terminal 5 detects the signal CI, then the DC loop is formed as L1 Cml1 relay contact (d) R2 transformer T1 Cml2 D3 PC3 L2. Then, data trans mitter and receivers connected to secondary terminals MT and MR of T1 transmit and receive data to and from a center device, etc., through the circuit. |
