Direct station selection private intercom exchange system

Claim 2

A key telephone system comprising, in Combination, a plurality of key telephone sets each including a handset, a hybrid, and a plurality of manually operable switch appearances for outside lines and direct station selectable intercom lines, each of said sets including a respective manually operable switch appearance for a common intercom answer line whereby a calling intercom station is connected to said set by the operation of said last named switch, each of said line appearances of said outside, intercom and answer lines including a respective tip lead and ring lead, each of said sets including conferencing means including a manually operable switch for completing a connection between said answer line and any other line having an appearance at that set, means connected across said respective tip and ring leads for ensuring privacy of all calls irrespective of momentary voltage peaks or battery open intervals, and common equipment shared by all of said sets comprising key system line circuits, signaling means and local battery means.

Claim 3

Apparatus in accordance with claim 1 wherein each of said line appearances of said outside lines and of said intercom lines includes a respective signal lead extending to a first or to a second terminal, respectively, and means whereby any one of said appearances of said intercom lines may be changed to the other by changing said lead from one of said terminals to the other of said terminals with no wiring changes being required in said common equipment.

Claim 4

Apparatus in accordance with claim 1 wherein said privacy means comprises a circuit having first and second input points and first and second output points, one of said inputs being connected to said tip lead of each of said appearances with the exception of said answer lines appearance and said second input being connected to said ring lead of each of said appearances by way of a switchhook contact, one of said outputs being connected directly to said handset and hybrid of the set, said second output point being connected to said handset and hybrid by way of dial contacts, and the tip lead of said answer line being connected directly to said first output point.

Claim 5

Apparatus in accordance with claim 3 wherein said circuit interposes first solid-state switching means between said first input point and said first output point and second solid-state switching means between said second input point and said second output point.

Claim 6

Apparatus in accordance with claim 4 wherein said switches comprise PNPN devices.

Claim 7

Apparatus in accordance with claim 1 wherein said privacy means comprises means responsive to normal battery voltage at any of said appearances for completing a path from said last named appearance to said hybrid of said set after a fixed preselected time delay.

Claim 8

Apparatus in accordance with claim 6 wherein said privacy means further includes means responsive to the operation of said path-completing means followed by removal of battery from said last named appearance for a time not exceeding a preselected duration, followed by the abrupt opening of said path-completing means, followed by the return of said battery for reoperating said path-comprising means after a variable preselected time delay, the length of said last named delay being determined by the length of said last named delay being determined by the length of said last named duration but not exceeding said last named duration, thereby precluding a set from seizing a line during a brief battery removal from a set first connected to that last named line.

Claim 9

A key telephone system comprising, in combination, a plurality of key telephone sets each including a plurality of first pushbutton means for connecting to outside lines and a plurality of second pushbutton means for the direct station selection of intercom lines, common equipment including a plurality of key system line circuits, signaling means and local battery means, each of said line circuits being connected to a respective one of said pushbutton Means, and each of said sets including a voice network and respective privacy circuit means including means responsive after a first fixed preselected delay to the detection of normal battery voltage on one of said lines for completing a talking path between one of said pushbutton means and said voice network of that set thereby precluding connection of a set to an already busy line as the result of sudden voltage surges or dialing pulses, said privacy circuit means further including means for closing said talking path responsive after a second variable delay to the sequence of the completion of said talking path, the opening of said path owing to the removal of battery for a period not exceeding a preselected duration and the return of said battery, the duration of said variable delay being determined by the length of said last named preselected duration but not exceeding said first fixed preselected delay.

Claim 10

A key telephone system comprising, in combination, a plurality of key telephone sets each including a plurality of first pushbutton means for connecting to outside lines and a plurality of second pushbutton means for the direct station selection of intercom lines, common equipment including a plurality of key system line circuits, signaling means and local battery means, each of said line circuits being connected to a respective one of said pushbutton Means, and each of said sets including a voice network and respective privacy circuit means including means responsive after a first fixed preselected delay to the detection of normal battery voltage on one of said lines for completing a talking path between one of said pushbutton means and said voice network of that set thereby precluding connection of a set to an already busy line as the result of sudden voltage surges or dialing pulses, said privacy circuit means further including means for closing said talking path responsive after a second variable delay to the sequence of the completion of said talking path, the opening of said path owing to the removal of battery for a period not exceeding a preselected duration and the return of said battery, the duration of said variable delay being determined by the length of said last named preselected duration but not exceeding said first fixed preselected delay.

Claim 11

Apparatus in accordance with claim 8 wherein said talking path closing means comprises first and second switch means on the tip and ring side of the line, respectively.

Claim 12

Apparatus in accordance with claim 9 wherein said first and second switch means comprise PNPN junction devices.