Automatic call transfer circuit for a plurality of telephones
Patent 4000375 Issued on December 28, 1976. Estimated Expiration Date: 
December 28, 1993. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
December 28, 1993. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.Patent References 3514544 3530253 3651274 3725595 InventorApplicationNo. 551511 filed on 02/20/1975US Classes:379/184LockoutExaminersPrimary: Robinson, Mark A.Attorney, Agent or FirmAbstractAn 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. | |
