Telephone interface circuit

Details Telephone interface circuit Telephone interface circuit

1991-11-21

1994-05-24

Dwyer, James L.

Telephonic communications

Telephone line or system combined with diverse electrical...

To produce visual-graphic copy

379102, 379399, 379393, 379105, 379377, H04M 1100

Patent

active

053156447

ABSTRACT:
A circuit for interfacing a host telephone system having a trunk line pair with a central office line pair and an additional circuit line pair includes a loop current monitor circuit for monitoring the host telephone system trunk line pair which is normally connected to the central office line pair. The loop current monitor provides a status signal output indicating the presence or absence of loop current. A relay controller receives the status signal and provides a relay control signal and a hold signal. A relay selectively connects the host telephone system trunk line pair to the additional circuit line pair in response to the relay control signal when loop current is detected after the host telephone goes off-hook. A hold termination circuit receives the hold signal and traps any loop current signals which may be detectable over the central office line pair. The relay controller circuit is active to generate the relay control signal only for an initial time period after the host telephone system goes off-hook.

REFERENCES:
patent: 3978468 (1976-08-01), Bond et al.
patent: 4538031 (1985-08-01), Beming et al.
patent: 4731821 (1988-03-01), Jackson, III
patent: 4788714 (1988-11-01), Hasimoto
patent: 4821312 (1989-04-01), Horton et al.
patent: 4893331 (1990-01-01), Horiuchi et al.
patent: 5113432 (1992-05-01), Van Stantbrink et al.

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