1977-03-14
1978-07-18
Cooper, William C.
H04M 100
Patent
active
041017412
ABSTRACT:
A line circuit for a key telephone system using two relays, a ring delay (B) and a combined off-hook and hold relay (C), and solid state devices including a first and a second optical coupler. On a ring signal from the exchange, the first optical coupler is activated to cause the energization of the ring relay. On a station of the line going off-hook (busy), the conventional A lead ground operates the C relay and causes de-energization of the B 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 sensing the line voltage as low (continued loop closure at the start of hold) or high (open loop at the stations of the line). The C relay is held during this determination so that the circuit may enter the hold condition when indicated. On a high voltage condition, indicating a hang-up condition, the second coupler switches on to prevent the B relay from operating, and thereby preventing the circuit from entering the hold condition.
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.
Brigance Gerald L.
Chaban Marvin M.
Cooper William C.
International Standard Electric Corporation
Raden James B.
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