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

• Current Assignee: Viking Electronics, Inc. (Eaton Corporation PLC.)
• Original Assignee: Viking Electronics, Inc. (Eaton Corporation PLC.)
• Inventors: Springer, Don C.
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Brigance, Gerald L.
• Application Number:
  US05/563,710
• Time in Patent Office: 638 Days
• Field of Search: 179/18 AD, 179/18 BC, 179/99, 179/30, 179/39, 179/17 B, 179/18 DA
• US Class Current: 379/184
• CPC Class Codes: H04M 9/002 with subscriber controlled access to a line, i.e. key telephone systems

Abstract

A privacy device for a telephone to prevent, unless desired, another telephone from being connected to the pair of incoming lines to which the telephone is connected. The privacy device employs voltage responsive means which is effective upon the telephone being connected to the incoming lines to establish a low impedance connection to the telephone only if the voltage across the incoming lines has initially at least a predetermined value. The low impedance connection drops the voltage across the incoming lines so that other telephones with the privacy device cannot be connected thereto. Means are provided for temporarily increasing the impedance across the lines to increase the voltage so that another telephone can be connected to the line when desired. This is done in a manner not to interrupt the connection between the lines but to maintain a minimum amount of current flowing therethrough so that the central office equipment does not detect an interruption in the line.

The privacy device is also equipped with means for turning it on regardless of the voltage across the lines when it is desired to use the telephone for intercommunication purposes within an office. When the intercommunication switch is pushed, the privacy device is caused to become conductive even though the value of the voltage across the lines is below the predetermined value.

Claims

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, and

a 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.

2. The combination of claim 1 in which each receiver assembly of each telephone includes both a receiver and a transmitter and in which the privacy device is connected between both the receiver and transmitter of each telephone and any pair of input lines connected thereto so that when said receiver is connected by said voltage responsive means to said pair of input lines, said transmitter is also so connected.

3. The combination of claim 1 in which the manually operable means comprises a manually operated electrical switch and an impedance connected to said voltage responsive means between the terminals of said switch so that when said switch is closed said impedance is effectively short circuited to alter the effect of said impedance upon the impedance in series with said receiver.

4. The combination of claim 3 in which said manually operated switch is normally closed and in which said impedance is connected in series with said main control switch so that when said manually operated switch is opened said impedance is effectively connected in series with said receiver to restore the voltage across said pair of input lines to at least said predetermined value.

5. The combination of claim 1 in which there are a plurality of pairs of input lines, switching means associated with each telephone for connecting the receiver of that telephone to any one of said plurality of pairs of input lines, said privacy device being connected between each such switching means and the receiver of the telephone so that the privacy device is effective regardless of which of said pairs of input lines said receiver is connected to.

6. The combination of claim 1 in which the receiver of the telephone is in a hand set and in which said main control switch is a hook switch which is closed upon removal of the hand set from its normal non-talking position.

7. The combination of claim 1 in which there are a pair of lines to which each of said telephones is adapted to be connected for maintaining an intercommunication call, in which each telephone has intercommunication switching means for connecting said receiver to said pair of lines in series with said privacy device, and in which means controlled by said intercommunication switching means is effective upon actuation of said intercommunication switching means to cause the privacy device of that telephone to establish said low impedance connection to the receiver even though the voltage across said pair of lines is below said predetermined value.

8. The combination of claim 1 in which the voltage responsive means includes a bi-directional electronic switch having a control electrode, said switch being connected in series between one of said input lines and said receiver, and control means for applying to said control electrode a signal dependent upon the voltage across said pair of input lines to cause said bi-directional switch to become conductive when said voltage has at least said predetermined value, said bi-directional switch having a relatively low impedance when conductive.

9. The combination of claim 8 in which there is a separate one of said bi-directional electronic switches in series with each of said input lines and said receiver and in which said control means is effective to cause both of said switches to become conductive when the voltage across said lines has at least said predetermined value.

10. The combination of claim 1 in which the voltage responsive means includes a bi-directional electronic switch having a relatively low impedance when conductive, said bi-directional switch being in series with said receiver and effective to establish said low impedance connection to said receiver when the voltage applied thereacross is above a break down value as a result of the voltage across the pair of input lines having at least said predetermined value, said bi-directional electronic switch having a control electrode effective when a proper signal is applied thereto to cause said bi-directional switch to become conductive even though the voltage across said input lines is below said predetermined value, and means including a switch operable when closed to apply said proper signal to said control electrode.

11. The combination of claim 1 in which said manually operable means is normally closed switch in series with said receiver between said circuit maintaining means and said receiver so that the opening of said normally closed switch increases the impedance between said pair of input lines while not interrupting the connection therebetween.

12. The combination of claim 1 in which the voltage responsive means includes a pair of bi-directional electronic switches, each having a control electrode and each being connected in series with a different one of said input lines, and means responsive to the voltage across said pair of input lines to cause a current flow through the control electrodes of each of said bi-directional switches to cause said switches to become conductive when the voltage across said pair of input lines is above said predetermined value.

13. The combination of claim 12 in which the means for controlling the current through said control electrodes comprises a pair of diodes connected back to back between said control electrodes, one of said diodes being a Zener diode, so that when the voltage across the lines exceeds the reverse breakdown voltage of said Zener diode, current flows through said control electrodes.

14. The combination of claim 13 in which means is provided for substantially short circuiting the Zener diode when the telephone is to be used for intercommunication purposes.

15. The combination of claim 1 in which said voltage responsive means includes a constant current, high impedance device connected in a circuit substantially in parallel with said receiver to minimize the effect of such voltage responsive means upon normal modulation of the current flowing through said receiver.

16. In combination with a telephone system of the type wherein there is one pair of input lines and another pair of lines used for intercommunication purposes,

a plurality of telephones adapted to be connected to one or the other of such pairs of lines, each telephone having a main control switch, a first selector switch for connecting said telephone to said pair of input lines, an intercommunication switch for connecting said telephone to said pair of intercommunication lines, 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, and

a privacy device connected in series with said main control switch between the receiver of each telephone and any pair of 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 the selected pair of lines to establish a relatively low impedance connection of the receiver of said telephone to said pair of lines through said electronic switch, said voltage responsive means being effective to prevent the connection of said receiver to said pair of lines when the voltage across the pair of 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 lines;

means independent of said main control switch for causing said electronic switch to become conductive to connect said receiver to the selected pair of lines even though the voltage across said pair of lines is below said predetermined value; and

means controlled by said intercommunication switch for causing said last named means to be effective so that upon the user of any telephone actuating the intercommunication switch of that telephone and the main control switch thereof, the receiver of said phone is connected to said pair of intercommunication lines even though the voltage across said pair of lines is below said predetermined value.