US3828141A
Expired / Lapsed
US
⏱️ 0.0 years remaining
System for detecting dial-generated and pushbutton-generated selection pulses
Assignee: Italtel SpA
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Filing: 1972-06-20
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Granted: 1974-08-06
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Expires: 1992-06-20
Abstract
Abstract In order to discriminate between true and spurious key signals in a telephone system in which a d-c subscriber line is independently closable by separate hook switches in series with a dial-type and a pushbutton-type digit selector, an exchange serving this line includes a low-level current sensor and an intermediate-level current sensor working into a coincidence circuit. In the presence of an output from the intermediate-level sensor with simultaneous absence of an output from the low-level sensor, the coincidence circuit connects the line wires across a voice-frequency tone receiver unless a transient condition is simultaneously indicated by the output of a differentiator connected across a pair of resistors in a branch circuit containing the two level sensors. A relay actuated by the output of the coincidence circuit disables the differentiator upon the detection of a key signal.
Inventors
- 👤 Marco F De
- 👤 C Manghi
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 15:35
CPC Classifications
H; H04; H04Q; H04Q3/00; H04Q1/00; H04Q1/18; H04Q1/30; H04Q1/44; H04Q1/444; H04Q1/45; H04Q1/453; H04Q1/4535
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
227 words
A system for discriminating between true and spurious key signals in a telephone line provided with hook-switch means establishing a relatively high line-current level in a closed condition and a relatively low line-current level in an open condition thereof, said line extending between a subscriber station provided with digit-selection means including pushbutton equipment and an exchange provided with a receiver for voicefrequency tones produced upon operation of said equipment, such operation generating a key signal represented by an intermediate line-current level in the closed condition of said hook-switch means, comprising: a low-level first current sensor connected to said line at said exchange and responsive to the open condition of said hookswitch means but nonresponsive to the presence of said key signal; an intermediate-level second current sensor connected to said line at said exchange and responsive to both the presence of said key signal and the open condition of said hook-switch means; normally unoperated switch means at said exchange operable to connect said receiver across said line; a coincidence circuit at said exchange connected to said current sensors for operating said switch means upon simultaneous presence of an output from said second sensor and absence of an output from said first sensor; and transition-detecting means in said coincidence circuit for preventing operation of said switch means upon a brief passage of the line current through said intermediate level.
Claim 2
Independent Claim
227 words
A system for discriminating between true and spurious key signals in a telephone line provided with hook-switch means establishing a relatively high line-current level in a closed condition and a relatively low line-current level in an open condition thereof, said line extending between a subscriber station provided with digit-selection means including pushbutton equipment and an exchange provided with a receiver for voicefrequency tones produced upon operation of said equipment, such operation generating a key signal represented by an intermediate line-current level in the closed condition of said hook-switch means, comprising: a low-level first current sensor connected to said line at said exchange and responsive to the open condition of said hookswitch means but nonresponsive to the presence of said key signal; an intermediate-level second current sensor connected to said line at said exchange and responsive to both the presence of said key signal and the open condition of said hook-switch means; normally unoperated switch means at said exchange operable to connect said receiver across said line; a coincidence circuit at said exchange connected to said current sensors for operating said switch means upon simultaneous presence of an output from said second sensor and absence of an output from said first sensor; and transition-detecting means in said coincidence circuit for preventing operation of said switch means upon a brief passage of the line current through said intermediate level.
Claim 3
Dependent Claim
34 words
A system as defined in claim 1 wherein said transition-detecting means comprises a differentiator with input connections to said line and gate means blockable by said differentiator in response to variations in line current.
Claim 4
Dependent Claim
32 words
A system as defined in claim 2 wherein said input connections include a pair of branch conductors of said line provided with respective impedances, said differentiator having inputs connected to said impedances.
Claim 5
Dependent Claim
38 words
A system as defined in claim 3 wherein each of said impedances comprises a resistor in series with a respective inductor, the inputs of said differentiator being connected to the junctions of each resistor with its associated inductor.
Claim 6
Dependent Claim
28 words
A system as defined in claim 3 wherein each of said sensors comprises an electromagnetic core with a pair of windings respectively in series with said branch conductors.
Claim 7
Dependent Claim
36 words
A system as defined in claim 2, further comprising disabling means for said differentiator controlled by said switch means to prevent a blocking of said gate means in response to minor fluctuations of said key signal.
Claim 8
Dependent Claim
34 words
A system as defined in claim 1 wherein said digit-selection means includes a dialing disk independent of said pushbutton equipment, said first sensor being responsive to line-current interruptions due to operation of said disk.
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) | 1977-08-05 | 1978-02-04 | 1978-08-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-08-05 | 1982-02-04 | 1982-08-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-08-05 | 1986-02-04 | 1986-08-06 | $7700.00 | Window Closed / Lapsed |