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Key telephone system having automatic exclusion circuit for line privacy

  • US 4,218,590 A
  • Filed: 01/29/1979
  • Issued: 08/19/1980
  • Est. Priority Date: 01/29/1979
  • Status: Expired due to Term
First Claim
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1. An exclusion circuit for establishing line privacy in a key telephone system of the type having a plurality of control units, one for each of a plurality of phone stations, for connecting a selected one of two or more telephone lines to a phone set at each such station, and wherein each control unit includes for each available telephone line, a line switching device for connecting the associated telephone line to the station set, a line condition sensing means for sensing the conditions of on-hook, off-hook and hold on the associated telephone line, and a latching circuit for each line switching device that responds to a line selector switch and to the line condition sensing means to operate and latch the associated line switching device in a state that connects the associated line to the station phone set, wherein said exclusion circuit is provided in at least one of said control units for at least a given telephone line and comprises in combination therewith:

  • a signal controlled gate means connected in circuit with the line selector switch and the latching circuit that are associated with said given telephone line, said gate means having a quiescent mode in which said line selector switch is effective, when actuated, to cause said latching circuit means to operate said line switching device, and having an exclusion mode in which said latching circuit means is unresponsive to actuation of said line selector switch; and

    timing circuit means connected to said signal controlled gate means and to the sensing means associated with said given line for disposing said gate means in said quiescent mode when said line condition sensing means senses either an on-hook or hold condition on the given telephone line, and for disposing said gate means in said exclusion mode after a first predetermined delay interval from the time that said sensing means senses an off-hook condition on the given line.

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