Line card circuit

Details Line card circuit Line card circuit

1974-11-11

1976-06-22

Robinson, Thomas A.

179 81R, H04M 121

Patent

active

039653080

ABSTRACT:
An improved line card circuit usable with key telephone systems is adapted to permit a message to be automatically transmitted from a subscriber key telephone station when operated to place a telephone line in a hold condition. A coupling circuit interfacing the message source and the telephone line during the hold condition of the line provides a high degree of cross-talk isolation. The coupling circuit also has the feature of automatically limiting to a predetermined level the power of the output signal supplied to the telephone line. A strappable option is provided by the coupling circuit to permit its operation with a standard eight ohm high fidelity amplifier source as well as with a 70 volt intercom systems. The line card circuit, besides these features, includes circuitry to allow full supervisory control of a telephone line to be exercised by a user of the subscriber key telephone when such unit is not in the hold condition. The line card circuit also includes circuitry that controls the operation of audible and visual indicators of an associated key telephone.

REFERENCES:
patent: 3076871 (1963-02-01), Bauman
patent: 3246082 (1966-04-01), Levy
patent: 3789803 (1974-02-01), Davis et al.
patent: 3794774 (1974-02-01), Kemmerly et al.

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