Patent US3909554A successfully refreshed from Google Patents.
US3909554A
Expired / Lapsed
US
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Control circuit for key telephone system
Assignee: Lordel Manufacturing Co
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Filing: 1974-08-23
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Granted: 1975-09-30
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Expires: 1994-08-23
Abstract
Abstract A key telephone system control circuit includes completely solid-state circuitry for performing all internal logical operations of the circuit and a pair of high current relays for performing the output functions of the control circuit. The solid-state circuitry produces one or more of three different control signals in response to various conditions on a telephone line pair to which a key telephone system is connected and in response to various conditions of the key telephone system. The three control signals control the operation of the two relays to generate all output functions required for the key telephone system. The control circuit includes holding circuitry having a latching device for producing one of the control signals indicative of the holding status of the line pair.
Inventors
- 👤 John M Reed
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 09:50
CPC Classifications
H; H04; H04M; H04M9/00; H04M9/002; H04M9/005; H04M9/006
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
429 words
In combination in a key telephone system, a control circuit comprising a telephone line pair connected to a telephone switching office and to a key telephone set receiver, a ringing current detection circuit responsive to ringing current on said line pair for generating a first control signal, an off-hook detection circuit responsive to a certain signal being applied to the A lead associated with said line pair for generating a second control signal, a holding circuit responsive to the coincidence of the application of said certain signal to the A lead and the flow of current in at least one line of said line pair, followed by the removal of said certain signal from the A lead, for generating a third control signal, first relay means operable in response to either said first or third control signals, second relay means operable in response to either said second or third control signals, means for applying current from a current supply to the interrupter motor of the key telephone system, for applying lamp-flash current from a current supply to the key telephone system line lamp associated with said line pair, and for applying ringer or buzzer current from a current supply to the ringer or buzzer of the key telephone system when said first relay means is operated and said second relay means is unoperated, means for applying steady-lamp current from a current supply to the key telephone system line lamp when said second relay means is operated and said first relay means is unoperated, and means for conducting current between said line pair and for applying lamp-wink current from a current supply to the key telephone system line lamp when said first and second relay means are operated, and wherein said holding circuit includes first logic means coupled to said A lead for producing a first logical signal if said certain signal is placed on the A lead for longer than a predetermined period of time, line current detecting means coupled to one line of the pair for producing a second logical signal substantially immediately when line current flows in said one line and for producing a third logical signal if the line current flows in said one line for longer than a certain period of time, second logic means responsive to the coincident production of said first, second and third logical signals for producing a fourth logical signal, and binary latch means responsive to the removal of said certain signal from the A lead and production of said third and fourth logical signals for generating said third control signal.
Claim 2
Dependent Claim
429 words
In combination in a key telephone system, a control circuit comprising a telephone line pair connected to a telephone switching office and to a key telephone set receiver, a ringing current detection circuit responsive to ringing current on said line pair for generating a first control signal, an off-hook detection circuit responsive to a certain signal being applied to the A lead associated with said line pair for generating a second control signal, a holding circuit responsive to the coincidence of the application of said certain signal to the A lead and the flow of current in at least one line of said line pair, followed by the removal of said certain signal from the A lead, for generating a third control signal, first relay means operable in response to either said first or third control signals, second relay means operable in response to either said second or third control signals, means for applying current from a current supply to the interrupter motor of the key telephone system, for applying lamp-flash current from a current supply to the key telephone system line lamp associated with said line pair, and for applying ringer or buzzer current from a current supply to the ringer or buzzer of the key telephone system when said first relay means is operated and said second relay means is unoperated, means for applying steady-lamp current from a current supply to the key telephone system line lamp when said second relay means is operated and said first relay means is unoperated, and means for conducting current between said line pair and for applying lamp-wink current from a current supply to the key telephone system line lamp when said first and second relay means are operated, and wherein said holding circuit includes first logic means coupled to said A lead for producing a first logical signal if said certain signal is placed on the A lead for longer than a predetermined period of time, line current detecting means coupled to one line of the pair for producing a second logical signal substantially immediately when line current flows in said one line and for producing a third logical signal if the line current flows in said one line for longer than a certain period of time, second logic means responsive to the coincident production of said first, second and third logical signals for producing a fourth logical signal, and binary latch means responsive to the removal of said certain signal from the A lead and production of said third and fourth logical signals for generating said third control signal.
Claim 3
Dependent Claim
64 words
The circuit of claim 1 wherein said first logic means includes a first capacitor and a first resistor coupled in series to the A lead, and a NAND gate whose input is coupled to the junction of said first capacitor and first resistor, said NAND gate being operable to produce the first logical signal when the first capacitor charges to a predetermined voltage level.
Claim 4
Dependent Claim
106 words
The circuit of claim 2 wherein said line current detection means comprises an optically-coupled isolator, the diode of which is coupled to one line of said line pair, a second resistor coupled to the collector of the transistor of said isolator, a second capacitor coupled in a series with the second resistor, said transistor assuming a conducting condition when line current flows in said one line to thereby produce the second logical signal, and said second capacitor charging to a predetermined voltage level when line current flows in said one line for longer than a predetermined period of time to thereby produce said third logical signal.
Claim 5
Dependent Claim
70 words
The circuit of claim 3 wherein said second logic means comprises a NOR gate having three inputs, one of which is coupled to the collector of said transistor and another of which is coupled to the junction between said resistor and said second capacitor, a third capacitor coupled to the third one of said inputs, and a third resistor coupling the output of said NAND gate to said third input.
Claim 6
Dependent Claim
135 words
The circuit of claim 3 wherein said latch means comprises second and third NOR gates, said second NOR gate having three inputs, one of which is coupled to the junction of said second resistor and second capacitor, a second of which is coupled to the junction of said first resistor and first capacitor, and a third of which is coupled to the output of said third NOR gate, said third NOR gate having a pair of inputs, a first of which is coupled to the output of said second NOR gate and a second of which is coupled to the output of said first NOR gate, and a second NAND gate whose input is coupled to the output of said second NOR gate, and whose output is coupled to said first and second relay means.
Claim 7
Dependent Claim
89 words
The circuit of claim 1 wherein said ringing current detection circuit comprises a diode coupled to one line of the line pair, a neon gas discharge tube coupled in series with the diode, a capacitor coupled in series between the gas discharge tube and ground potential, a pair of NAND gates coupled in series and whose input is coupled to the junction between the capacitor and the gas discharge tube, said NAND gates generating said first control signal when the charge on said capacitor exceeds some predetermined threshold level.
Claim 8
Dependent Claim
39 words
The circuit of claim 6 wherein said ringing current detection circuit further comprises capacitor discharge means including a resistor and diode coupled in series between the A lead and the junction of said gas discharge tube and said capacitor.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-09-29 | 1979-03-31 | 1979-09-30 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-09-29 | 1983-03-31 | 1983-09-30 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-09-29 | 1987-03-31 | 1987-09-30 | $7700.00 | Window Closed / Lapsed |