Line circuit for key telephone systems

Details Line circuit for key telephone systems Line circuit for key telephone systems

1977-03-14

1978-07-18

Cooper, William C.

H04M 100

Patent

active

041017404

ABSTRACT:
A line circuit for a key telephone system using as the main operative components, two relays i.e. a ring relay and a combined off-hook and hold relay and an optical coupler and rectifier bridge combination. On a ring signal from the exchange, the optical coupler is activated to cause the energization of the ring relay. On a station of the line going off-hook, the conventional A lead ground operates the off-hook relay and causes de-energization of the ring relay. When a station of the line goes into hold, the circuit must differentiate this condition from a hang-up condition. This differentiation is performed by the coupler sensing the line voltage as low or high. The line voltage is high if the line loop is open indicating a hang-up condition. The line voltage is low if the line loop is still closed during the sensing period as a preliminary to the hold condition. The off-hook relay is held during this sensing operation so that the circuit may enter the hold condition when indicated.

REFERENCES:
patent: 3764752 (1973-10-01), Yachabach
patent: 3766325 (1973-10-01), Hatfield et al.
patent: 3856994 (1974-12-01), Ozechoski
patent: 3914556 (1975-10-01), Frazee
patent: 4004106 (1977-01-01), Yachabach
patent: 4039763 (1977-08-01), Angner
patent: 4064373 (1977-12-01), Pinede et al.

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