Key telephone system

Details Key telephone system Key telephone system

1975-10-17

1977-05-17

Claffy, Kathleen H.

179 18FA, H04M 100

Patent

active

040243532

ABSTRACT:
A line circuit for a key telephone system is provided with a first relay normally energized and a second relay for speech supervision. The operation of the first relay establishes a circuit for holding the second relay and the first relay is released by the voltage drop of a control line normally connected to a line holding control circuit and a visual indication circuit, respectively, at the manual operation of a non-lock type hold key to establish an intermittent signal for line holding indication. A switching transistor is provided in a circuit including the first relay so that the first relay is not energized by the signal intermitently sent to the visual indication circuit, so as to control the line hold control circuit and the visual indication circuit by one control line.

REFERENCES:
patent: 3239610 (1966-03-01), Morse et al.
patent: 3453396 (1969-07-01), Lacey et al.
patent: 3739104 (1973-05-01), O'Neill
patent: 3865995 (1975-02-01), Kerman et al.
patent: 3887774 (1975-06-01), Takubo et al.
patent: 3895192 (1975-07-01), Angner et al.
patent: 3916116 (1975-10-01), McEowen

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