Telephone party line circuit - has voltage monitoring circuit providing signal to switch off answering machine for A=subscriber and switch on B=subscriber's appts.

摘要

A main (HA) and second (NA) subscriber station are connected to twin lines (La,Lb). A telephone answer machine (AB) is integrated with the main station (HA) via transformer (U) and a relay contactor (r1) of a relay (R) controlled by a call signal responder unit (RAS). There is no problem as far as the ability of the main station is concerned to take over from the telephone answering machine. The second station (NA) on lifting its receiver from the contactor (gmIV) cannot thereby stop the recorder. Relay contactors (r2,r3) connected the speech circuit (SNA) to a d.c. supply source (-U) via a resistor (R1). The voltage drop is sensed (SUS) and a positive voltage applied to gate (G1,G2) and to the responder unit (TAS) which causes the relay (R) to de-energise. This results in the telephone answering machine being disconnected and simultaneously connected the second telephone station on line with the calling party.