US3647983A — Key system line card circuit

Claim 1

Independent Claim 144 words

A line card circuit for a telephone system which includes a subscriber line formed by a pair of line conductors interconnecting a central office with a subscriber station set, the subscriber set having means for looping the line conductors to provide a current loop, said circuit comprising: sensing means responsive to ringing signals in said line conductors to be operated thereby, said sensing means including means responsive to current and a rectifier bridge selectively connected to each of said line conductor pair or to ground, said rectifier having first and second output terminals providing rectified outputs responsive to receipt by said bridge of ringing signals; means responsive to the operation of said sensing means and electrically isolated from said ringing signals for initiating local signaling; and means responsive to the operation of said sensing means for maintaining said local signaling for a preselected period.

Claim 2

Dependent Claim 144 words

A line card circuit for a telephone system which includes a subscriber line formed by a pair of line conductors interconnecting a central office with a subscriber station set, the subscriber set having means for looping the line conductors to provide a current loop, said circuit comprising: sensing means responsive to ringing signals in said line conductors to be operated thereby, said sensing means including means responsive to current and a rectifier bridge selectively connected to each of said line conductor pair or to ground, said rectifier having first and second output terminals providing rectified outputs responsive to receipt by said bridge of ringing signals; means responsive to the operation of said sensing means and electrically isolated from said ringing signals for initiating local signaling; and means responsive to the operation of said sensing means for maintaining said local signaling for a preselected period.

Claim 3

Dependent Claim 51 words

The circuit of claim 1 further comprising: a busy indication circuit at said line card location said circuit including a busy indication device for providing a busy indication signal; and means responsive to current in said loop and to the operation of said sensing means for energizing said busy indication circuit.

Claim 4

Dependent Claim 52 words

The circuit of claim 2 wherein said busy indication circuit further comprising: switch means in series electrical connection with said busy indication device whereby upon operation of said sensing means responsive to current in said loop and upon operation of said switch means said busy indication device provides a busy indication signal.

Claim 5

Dependent Claim 20 words

The circuit of claim 3 wherein said busy indication device is a lamp which upon energization provides a light signal.

Claim 6

Dependent Claim 23 words

The circuit of claim 1 further comprising: signal terminating means responsive to the operation of said looping means for terminating said local signaling.

Claim 7

Dependent Claim 31 words

The circuit of claim 5 further comprising: hold circuit preparing means responsive to the operation of said looping means for preparing a hold circuit for rapid connection across said line conductors.

Claim 8

Dependent Claim 61 words

The cIrcuit of claim 6 wherein said hold circuit comprises an impedance having first and second terminals, and wherein said hold circuit preparing means comprises: means for connecting said first terminal to one of said line conductors responsive to the operation of said looping means; and means for subsequently rapidly connecting said second terminal to the other of said line conductors.

Claim 9

Dependent Claim 32 words

The circuit of claim 1 wherein said sensing means comprises: a double wound relay having a first operating coil connected to receive and be operated by ringing signals in said subscriber line.

Claim 10

Dependent Claim 44 words

The circuit of claim 1 wherein said sensing means further comprises: a double wound relay having first and second windings, said first winding connected across said first and second bridge output terminals, said second winding connected in series electrical relationship with said current loop.

Claim 11

Dependent Claim 26 words

The circuit of claim 9 further comprising: a capacitor connected across said first winding for holding said relay activated during periods of low ringing signal level.

Claim 12

Dependent Claim 42 words

The circuit of claim 1 further comprising: switching means for selectively switching said sensing means between one of said line conductors and ground or the other of said line conductors and ground, whereby said subscriber line may be used for two-party operation.

Claim 13

Dependent Claim 16 words

The circuit of claim 8 further comprising: means for selectively varying the sensitivity of said relay.

Claim 14

Dependent Claim 34 words

The circuit of claim 12 wherein said selective sensitivity varying means comprises: a resistor connected in series electrical connection with said first operating coil; and means for selectively shorting out said series connected resistor.

Claim 15

Dependent Claim 104 words

A telephone line circuit for use with telephone systems characterized by at least one key telephone unit and a pair of line conductors adapted to be interconnected by operation of said key telephone unit, said telephone line circuit comprising: sensing means for detecting ringing signals applied to said line conductors, said sensing means including a rectifier for providing direct current signals in response to said ringing signals, and a first coil of a first relay having first and second coils, said first coil being responsive to said direct current signals from said rectifier, said second coil being connected in one of said line conductors.

Claim 16

Dependent Claim 104 words

A telephone line circuit for use with telephone systems characterized by at least one key telephone unit and a pair of line conductors adapted to be interconnected by operation of said key telephone unit, said telephone line circuit comprising: sensing means for detecting ringing signals applied to said line conductors, said sensing means including a rectifier for providing direct current signals in response to said ringing signals, and a first coil of a first relay having first and second coils, said first coil being responsive to said direct current signals from said rectifier, said second coil being connected in one of said line conductors.

Claim 17

Dependent Claim 93 words

The telephone line circuit defined by claim 14 wherein voice signals are applied to said line conductors when said telephone system is in use, and wherein said first coil enables activation of said line circuit in response to said direct current signals, said second coil enabling activation of said line circuit in response to interconnection of said paid of line conductors by operation of said key telephone unit, said line circuit further including capacitive means coupled in parallel to said second coil for rendering said second coil operatively unaffected by said voice signals.

Claim 18

Dependent Claim 47 words

The telephone line circuit defined by claim 14 further comprising: means, including a second relay responsive to operation of said first relay, for enabling ringing at said key telephone unit; and means, including said second relay for connecting a holding impedance between said pair of line conductors.

Claim 19

Dependent Claim 37 words

The telephone line circuit defined by claim 16 further comprising means for preventing ringing at said key telephone unit whenever said line conductors are interconnected by operation of said key telephone unit or by said holding impedance.

Claim 20

Dependent Claim 139 words

A telephone line circuit for use with telephone systems including at least one key telephone unit and a pair of line conductors to which ringing signals and line current are applied and which are adapted to be interconnected by operation of said key telephone unit, said telephone line circuit comprising: a full-wave rectifier having a pair of input terminals and a pair of output terminals, said input terminals being adapted to be connected betweeN said line conductors, said rectifier providing direct current signals at said output terminals in response to said ringing signals; and a first relay having first and second coils and a contact responsive to energization of one of said first and second coils, said first coil being connected to be energized by direct current signals, said second coil connected to be energized by said line current.

Claim 21

Dependent Claim 139 words

A telephone line circuit for use with telephone systems including at least one key telephone unit and a pair of line conductors to which ringing signals and line current are applied and which are adapted to be interconnected by operation of said key telephone unit, said telephone line circuit comprising: a full-wave rectifier having a pair of input terminals and a pair of output terminals, said input terminals being adapted to be connected betweeN said line conductors, said rectifier providing direct current signals at said output terminals in response to said ringing signals; and a first relay having first and second coils and a contact responsive to energization of one of said first and second coils, said first coil being connected to be energized by direct current signals, said second coil connected to be energized by said line current.

Claim 22

Dependent Claim 57 words

The apparatus defined by claim 18 further including: a ringing circuit including a second relay for selectively enabling ringing at said key telephone unit in response to operation of said contact; and a holding circuit including said second relay for connecting an impedance between said line conductors to have said line conductors maintained in a hold position.

Claim 23

Dependent Claim 47 words

The apparatus defined by claim 19 further including: means having a third relay for controlling the presence of visual indications at said key telephone unit when in operation; and means for maintaining said third relay in an energized condition when said key telephone unit is in operation.

Claim 24

Dependent Claim 121 words

A telephone line circuit for use with telephone systems including a key telephone unit and a pair of line conductors to which ringing signals and line current are applied and which are adapted to be connected through said key telephone unit by operation thereof, said telephone line circuit comprising: first means including a first relay for energizing said line circuit in response to said ringing signals or to the flow of said line current through said line conductors when interconnected; second means for enabling ringing at said key telephone unit in response to said ringing signals; and third means responsive to the operation of said key telephone unit for enabling the presentation of visual operation indicators at said key telephone unit.

Claim 25

Dependent Claim 121 words

A telephone line circuit for use with telephone systems including a key telephone unit and a pair of line conductors to which ringing signals and line current are applied and which are adapted to be connected through said key telephone unit by operation thereof, said telephone line circuit comprising: first means including a first relay for energizing said line circuit in response to said ringing signals or to the flow of said line current through said line conductors when interconnected; second means for enabling ringing at said key telephone unit in response to said ringing signals; and third means responsive to the operation of said key telephone unit for enabling the presentation of visual operation indicators at said key telephone unit.

Claim 26

Dependent Claim 53 words

The apparatus defined by claim 21 wherein said second means includes a second relay and said third means includes a third relay, said line circuit further comprising fourth means including said second and third relays for connecting an impedance between said line conductors to have said line conductors maintained in a hold condition.

Claim 27

Dependent Claim 30 words

The apparatus defined by claim 22 further comprising means for maintaining said third relay, once energized, in an energized condition for as long as said key telephone unit is operated.

Claim 28

Dependent Claim 67 words

The apparatus defined by claim 21 wherein said first relay includes first and second coils and a contact, said first coil being adapted to be energized in response to the presence of ringing signals, said second coil being adapted to be energized in response to the presence of line current, said contact being operated in response to the energization of either of said first and second coils.

Claim 29

Dependent Claim 36 words

The telephone line circuit defined by claim 21, said first means further including a rectifier connected between said line conductors for causing operation of said first relay in response to the presence of said ringing signals.

Claim 30

Dependent Claim 94 words

The telephone line circuit defined by claim 21, wherein voice signals are applied to said line conductors when said telephone system is used, said first relay including a first coil operatively connected between said line conductors and a second coil connected in one of said line conductors, said first coil being connected to be energized in response to the application of ringing signals to said line conductors, said second coil being energized by said flow of line current, said line circuit further including means for rendering said second coil insensitive to said voice signals.

Claim 31

Dependent Claim 194 words

A telephone line circuit for use with key telephone systems including at least one key telephone having a hold button and connected to a central facility by a pair of line conductors, said key telephone systems having a ringing condition during which ringing signals are applied to said line conductors, a seize condition characterized by said line conductors being interconnected by operation of said Key telephone, and a hold condition characterized by the connection of a holding impedance between said line conductors in response to operation of the hold button, line current being applied to said line conductors during said seize and hold conditions, said telephone line circuit comprising: ringing means for controlling ringing at the key telephone; first means for detecting ringing signals applied to said line conductors during said ringing condition and for controlling the ringing means to provide ringing at said key telephone, said first means being connected between the line conductors; and second means for detecting line current in said line conductors during said seize and hold conditions for controlling the ringing means to prevent ringing at the key telephone, said second means connected in one of said line conductors.

Claim 32

Dependent Claim 194 words

A telephone line circuit for use with key telephone systems including at least one key telephone having a hold button and connected to a central facility by a pair of line conductors, said key telephone systems having a ringing condition during which ringing signals are applied to said line conductors, a seize condition characterized by said line conductors being interconnected by operation of said Key telephone, and a hold condition characterized by the connection of a holding impedance between said line conductors in response to operation of the hold button, line current being applied to said line conductors during said seize and hold conditions, said telephone line circuit comprising: ringing means for controlling ringing at the key telephone; first means for detecting ringing signals applied to said line conductors during said ringing condition and for controlling the ringing means to provide ringing at said key telephone, said first means being connected between the line conductors; and second means for detecting line current in said line conductors during said seize and hold conditions for controlling the ringing means to prevent ringing at the key telephone, said second means connected in one of said line conductors.

Claim 33

Dependent Claim 193 words

The telephone line circuit defined by claim 27 further comprising holding means for placing the system in a hold condition, said holding means including: a holding impedance, and first and second switches connected in series with the holding impedance, the first and second switches serving to connect the holding impedance between said line conductors when both first and second switches are operated; said first means including: ringing signal detector means for detecting said ringing signals applied to said line conductors, and a first relay, operated by said ringing signal detector means for controlling said ringing means to provide ringing at said key telephone, said first relay also operated in response to operation of the hold button for operating the first switch of the holding means; said second means including: line current detector means for detecting the flow of line current in said line conductors, and a second relay operated by said line current detector means for controlling said ringing means to prevent ringing at said key telephone and for operating the second switch of the holding means, whereby the hold condition is only produced by concurrent operation of both first and second relays.

Claim 34

Dependent Claim 136 words

The telephone line circuit defined by claim 28 wherein said key telephone system also includes a ringer and a power source adapted to be controllably interconnected through said ringing means to provide ringing at the key telephone, said ringing means including: a ringing conductor for controllably interconnecting the ringer and the power source; and third and fourth switches connected in series in said ringing conductor for individually completing or breaking the continuity of the ringing conductor, said third switch being operated by said first relay to complete the continuity of said ringing conductor to allow interconnection of said ringer and power source by the ringing conductor, said fourth switch being operated by said second relay to break the continuity of the ringing conductor to prevent interconnection of the ringer and power source by the ringing conductor.

Claim 35

Dependent Claim 57 words

The telephone line circuit defined by claim 29, said line current detector means including a third relay connected in one of said pair of line conductors to be operated by line current in said line conductors, said third relay releasing the telephone system from said hold condition in response to a polarity reversal across said line conductors.

Claim 36

Dependent Claim 38 words

The telephone line circuit defined by claim 30, said ringing signal detector means including said third relay and a rectifier connected between said line conductors for causing operation of said third relay in response to said ringing signals.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1975-03-07	1975-09-06	1976-03-07	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1979-03-07	1979-09-06	1980-03-07	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1983-03-07	1983-09-06	1984-03-07	$7700.00	Window Closed / Lapsed

Key system line card circuit

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