Line use indicator for telephone sets sharing a single line

Details Line use indicator for telephone sets sharing a single line Line use indicator for telephone sets sharing a single line

1983-12-22

1985-10-08

Dwyer, James L.

179 17B, H04M 322

Patent

active

045462143

ABSTRACT:
Where several telephone sets are connected to a single telephone line, it would be convenient to have a visual indication that the line is in use, to avoid lifting a handset to see if there is a conversation, for example. A circuit is installed across the telephone line, the circuit having a voltage divider connected between Tip and Ring, a first transistor with its base connected to the center of the voltage divider, a second transistor with its base connected to the collector of the first transistor and a third transistor having its base connected to the emitter of the second transistor, with a light emitting device connected between either Tip or Ring conductor and the collectors of the second and third transistors. The light emitting device can be a light emitting diode. An optical coupler cooperative with the light emitting device can be used to turn on power to light emitting devices in all the telephones, from a separate power source.

REFERENCES:
patent: 3567867 (1971-03-01), Rice et al.
patent: 3920924 (1975-11-01), Layburn
patent: 3951248 (1976-04-01), Feiner et al.
patent: 4394544 (1983-07-01), De Leon

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