Line circuit for a universal key/internal telephone system

Details Line circuit for a universal key/internal telephone system Line circuit for a universal key/internal telephone system

1976-02-06

1977-03-22

Claffy, Kathleen H.

H04M 172

Patent

active

040138445

ABSTRACT:
A double coil relay has one coil coupled between the ring conductor and ground and the other coil coupled between the tip conductor and a negative direct current voltage. The tip and ring conductors are coupled to telephone subsets external to the line circuit. The double coil relay lights subset busy lamps external of the line circuit when a subset is off-hook. A branched telephone circuit is also provided for voice signals in a normal conversation mode with another telephone subset external of the line circuit coupled to another line circuit identical to the present line circuit and a selecting paging mode. A second single coil relay is coupled to the double coil relay to provide the normal conversation mode and to select the paging mode with the single coil relay disabling the conversation mode when the paging mode is selected. The two relays are operated by power supply voltages and polarities present in a conventional key telephone system service unit external of the line circuit.

REFERENCES:
patent: 3865995 (1975-02-01), Kerman et al.
patent: 3872261 (1975-03-01), Shinoi et al.

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