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Telephone privacy device

  • US 4,000,376 A
  • Filed: 03/31/1975
  • Issued: 12/28/1976
  • Est. Priority Date: 03/31/1975
  • Status: Expired due to Term
First Claim
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1. In combination with a telephone system of the type wherein there are one or more pairs of input lines,a plurality of telephones adapted to be connected to one or more such pairs of input lines, each telephone having a main control switch and a receiver assembly including a receiver electrically in series with said main control switch, said main control switch being closed when it is desired to talk, anda privacy device connected in series with said main control switch between the receiver of each telephone and any pair of input lines connected thereto, said privacy device comprising:

  • voltage responsive means including an electronic switch in series with said receiver and effective upon closure of the main control switch of the telephone to which said voltage responsive means is connected and upon the presence of a voltage of at least a predetermined value across a pair of input lines to establish a relatively low impedance connection of the receiver of said telephone to said pair of input lines through said electronic switch, said voltage responsive means being effective to prevent the connection of said receiver to said pair of input lines when the voltage across the pair of input lines is below said predetermined value so that upon said voltage drop being so reduced the privacy device of any other telephone is effective to prevent the receiver of said other telephone from being connected to said pair of input lines;

    manually operable means independent of said main control switch for increasing temporarily the impedance in series with said receiver so as to restore the voltage across said pair of input lines to at least said predetermined value to enable the privacy device of another of said telephones to connect the receiver of such other telephone to said pair of input lines; and

    means for maintaining a circuit between said pair of input lines while said manually operable means is operated so that the current flow between said input lines is always maintained above a predetermined minimum value.

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