Key telephone system line circuit

Details Key telephone system line circuit Key telephone system line circuit

H - Electricity

04

M

379/33, 379/67,

H04M 3/22 (2006.01) H04M 3/42 (2006.01) H04M 9/00 (2006.01)

Patent

CA 1049672

ABSTRACT OF THE DISCLOSURE A line card circuit providing supervisory functions in a key telephone system is disclosed. Two multi-contact relays perform all of the switching functions required to operate the audible and visual signaling devices used to indicate incoming calls, busy lines, and held calls, and to switch a shunt impedance across the line conductors to maintain line current when a call on that line is being held. Ringing voltage and line current are sensed by semiconductors which comprise the combination of light- emitting diodes and an adjacent light-responsive semiconductor switch. These optical semiconductors are interconnected with other semiconductor devices to form a logic circuit for actuating the two control relays, and for disabling the line current detec- tion circuit when the associated line is being held.

266055

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