| 摘要 |
PURPOSE:To enable to exercise various controls with a pair of control lines, by connecting an electro-acoustic conversion circuit and a light emitting display circuit including a signal amplifier in parallel between a pair of control lines connecting a main device and telephone sets. CONSTITUTION:A main device and telephone sets A, B, are connected with main trunk lines 28a, 28b and control lines 29a, 29b. Control terminals 31a, 31b connected to the control lines 29a, 29b of the telephone sets A, B, FFs consisting of transistors 35a, 35b, latching relay P and electro-acoustic conversion circuit including a speaker 45 and light emitting display circuit 51 are connected. In main trunk call and extension call, a signal in audible frequency band is transmitted via the control lines 29a, 29b from the main device to drive the speaker 45 and the circuit 51. In the display of busy call and holding display, a signal outside the audible frequency band is transmitted and only the circuit 51 is driven. |
