Line card circuit for key telephone system

Details Line card circuit for key telephone system Line card circuit for key telephone system

H - Electricity

04

M

379/33, 379/67

H04M 1/00 (2006.01) H04M 1/21 (2006.01) H04M 1/74 (2006.01)

Patent

CA 1055175

ABSTRACT OF THE DISCLOSURE: An improved line card circuit usable with key telephone system is adapted to permit a message to be automatically trans- mitted 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 auto- matically limiting to a predetermined level the power of the output signal supplied to the telephone line. A [stoppable] option is provided by the coupling circuit to permit its operation with a standard eight ohm high fidelity amplifier source as well as with at 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.

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