1978-12-06
1981-03-03
Brigance, Gerald L.
179 99E, H04Q 520
Patent
active
042543061
ABSTRACT:
A key telephone system, in which a key service unit is provided for selectively connecting a plurality of key telephone sets to a CO line by two control lines and a talking line. The key service unit is comprised of a DC power source having two terminals of a positive output voltage and a negative output voltage, a first detector connected to one of two control lines for detecting a state where one of the two output voltages is applied across the two control lines to flow a current of predetermined value therethrough, a first switch for connecting the other output voltage across the control lines in response to the output of the first detector, a second detector connected to the other of the two control lines for detecting a state where the other of the output voltages is applied across the two control lines to flow a current larger than a certain value therethrough, and a second switch for connecting the talking line to the CO line in response to the output of the second detector. Additional circuitry is further provided to perform the intercomm. talking operation, the holding operation for the CO line, and the privacy operation and other functions.
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Sekiguchi Kouichi
Takano Toshiichi
Adams Bruce L.
Brigance Gerald L.
Burns Robert E.
Iwasaki Tsushinki Kabushiki Kaisha
Lobato Emmanuel J.
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