Key telephone system line circuit

Details Key telephone system line circuit Key telephone system line circuit

1977-01-19

1978-06-06

Claffy, Kathleen H.

179 84A, H04M 172

Patent

active

040938301

ABSTRACT:
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 detection circuit when the associated line is being held.

REFERENCES:
patent: 3239610 (1966-03-01), Morse et al.
patent: 3283083 (1966-11-01), Mac Leod
patent: 3436488 (1969-04-01), Barbato
patent: 3647983 (1972-03-01), Fitzsimmons et al.
patent: 3764752 (1973-10-01), Yachabach
patent: 3766325 (1973-10-01), Hatfield et al.
patent: 3952169 (1976-04-01), Vincent
patent: 4004106 (1977-01-01), Yachabach et al.
"Model CE 400 KTU Line Card"; Technical Practices Bulletin C-303.001 Issue 2; Cook Electric Company; Sep. 1973.
"ITT 400 E Key Telephone Unit"; Specification KSP4-0-00E; International Telephone and Telegraph Corp.; Aug. 1973.
"General Electric Optoelectronics Manual"; General Electric Company; 1976; pp. 70-72.

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