Telephone line lockout device

Details Telephone line lockout device Telephone line lockout device

1994-05-11

1995-08-22

Chin, Stephen

Telephonic communications

Multi-line or key substation system with selective switching...

With exclusion or priority feature

379156, 379184, 379194, H04M 100, H04M 1300, H04M 300

Patent

active

054447720

ABSTRACT:
A telephone extension controller for permitting controlled access of telephone line from one of a given number of extension telephones coupled thereto when each extension telephone is controlled with the same comprising a lock-out circuit adapted to be coupled to a ring wire or a tip wire, the lock-out circuit further adapted for allowing a selected extension telephone of a plurality of extension telephones coupled to a telephone line to control and prevent the other extension telephones from accessing the telephone line when its switch hook is raised, the lock-out circuit including an optoisolator photo-coupled Darlington transistor having a conducting section and a photo-activated section and a Zener diode coupled in series with the conducting section of the Darlington transistor and coupled in parallel with the photo-activated section of the Darlington transistor.

REFERENCES:
patent: 4000375 (1976-12-01), Kawamura
patent: 4000376 (1976-12-01), Springer
patent: 4266103 (1981-05-01), White
patent: 4511767 (1985-04-01), Wetzel
patent: 4805210 (1989-02-01), Griffith
patent: 4807278 (1989-02-01), Ross
patent: 4809317 (1989-02-01), Howe
patent: 4899372 (1990-02-01), Wahi
patent: 5022068 (1991-06-01), Fujisaki

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