US4000375A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Automatic call transfer circuit for a plurality of telephones
Assignee: Individual
•
Filing: 1975-02-20
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Granted: 1976-12-28
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Expires: 1995-02-20
Abstract
Abstract An automatic call transfer circuit for a plurality of telephones which are connected in parallel respectively between a pair of telephone lines, relay coils each one of which is connected with a different one of the telephones respectively and condensers each one of which is connected in parallel with a different one of the relay coils respectively. Energizing of each one of the relay coils makes it possible to use only the telephone which is connected to the energized relay coil. The circuit further comprises a current holding circuit which has at least one Zener diode for holding a current between the telephone lines at a moment of call transfer between the telephones in a telephone conversation where the current is flowing in a prescribed single direction.
Inventors
- 👤 Hachishiro Kawamura
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 09:49
CPC Classifications
H; H04; H04M; H04M3/00; H04M3/42; H04M3/428; H04M3/4283
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
151 words
In a telephone system, an automatic call transfer circuit for a plurality of telephones comprising: first and second telephone lines; a plurality of telephone circuits normally connected in parallel across said first and second telephone lines, each of said telephone circuits including a telephone, a relay coil connected to each said telephone, said relay coil energizable by said telephone going off-hook, a condenser connected in parallel with each said relay coil, and means responsive to the energizing of said relay coil for disconnecting all other of said telephone circuits from parallel connection across said first and second telephone lines; and means for holding a current between said first and second telephone lines at a moment of call transfer from any one to another of said telephones in a conversation in which current flows through said first and second telephone lines, said current holding means including at least a first Zener diode.
Claim 2
Dependent Claim
151 words
In a telephone system, an automatic call transfer circuit for a plurality of telephones comprising: first and second telephone lines; a plurality of telephone circuits normally connected in parallel across said first and second telephone lines, each of said telephone circuits including a telephone, a relay coil connected to each said telephone, said relay coil energizable by said telephone going off-hook, a condenser connected in parallel with each said relay coil, and means responsive to the energizing of said relay coil for disconnecting all other of said telephone circuits from parallel connection across said first and second telephone lines; and means for holding a current between said first and second telephone lines at a moment of call transfer from any one to another of said telephones in a conversation in which current flows through said first and second telephone lines, said current holding means including at least a first Zener diode.
Claim 3
Dependent Claim
23 words
The automatic call transfer circuit for a plurality of telephones recited in claim 1 wherein: said current holding means includes a rectifying circuit.
Claim 4
Dependent Claim
24 words
The automatic call transfer circuit for a plurality of telephones recited in claim 1 wherein: said current holding means includes a second Zener diode.
Claim 5
Dependent Claim
57 words
The automatic call transfer circuit for a plurality of telephones recited in claim 1 including: means responsive to one of said telephones going off-hook in one of said plurality of telephone circuits for connecting said current holding means in series with said first telephone line and all telephones in each of the other of said telephone circuits.
Claim 6
Dependent Claim
52 words
The automatic call transfer circuit for a plurality of telephones recited in claim 4 including: a current limiter connected in series with said second telephone line and a telephone in one of said telephone circuits, wherein the resistance of said current limiter becomes a large value when a small current flows therethrough.
Claim 7
Dependent Claim
129 words
The automatic call transfer circuit for a plurality of telephones recited in claim 4 including: a plurality of current limiters, each of said current limiters being connected in series with said second telephone line and a respective telephone in one of said plurality of telephone circuits, wherein the resistance of each of said current limiters becomes a large value when a small current flows therethrough; and means for providing an alternate current path between said second telephone line and each of the respective telephones of said plurality of telephone circuits, said means including a normally closed contact in each of said plurality of telephone circuits, each said contact except one being opened when the receiver of the telephone is lifted up in a telephone circuit including said one contact.
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) | 1979-12-28 | 1980-06-28 | 1980-12-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-12-28 | 1984-06-28 | 1984-12-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-12-28 | 1988-06-28 | 1988-12-28 | $7700.00 | Window Closed / Lapsed |