Browse Prior Art Database

Telephone Line Current Interruption/Flashing

IP.com Disclosure Number: IPCOM000076204D
Original Publication Date: 1972-Jan-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Zoric, D: AUTHOR

Abstract

This circuit is used to interrupt the line current in a 2-wire telephone set for a short defined period of time. The current-interruption control signal is emitted after the dialing pulses when special signals, such as data signals, are to be transmitted to the exchange.

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Telephone Line Current Interruption/Flashing

This circuit is used to interrupt the line current in a 2-wire telephone set for a short defined period of time. The current-interruption control signal is emitted after the dialing pulses when special signals, such as data signals, are to be transmitted to the exchange.

By pressing key W, a positive pulse through C1 causes transistor T to conduct for about 2 microseconds, which, in turn, extinguishes the connected silicon-controlled rectifier (SCR) by diverting the line current from SCR. After a period of time defined by R3 and C2 has elapsed, SCR fires. D1 helps to discharge C2. Zener diode D2 defines the firing potential. The conductive period of T is made much shorter than the interruption period of SCR by adopting suitable values for resistors R1 and R2, together with C1 and R4.

This electronic circuit requires no third conductor or earth key for signaling, and contact bouncing of key W is eliminated by the time constant R2. C1 being appropriately chosen.

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