Electronic hold and hold-release circuit for a telephone set in

Details Electronic hold and hold-release circuit for a telephone set in Electronic hold and hold-release circuit for a telephone set in

1978-05-08

1979-09-25

Cooper, William C.

179 99H, H04M 100

Patent

active

041692160

ABSTRACT:
An electronic hold and hold-release circuit for a telephone set in a multiple extension single line telephone system has an indicator in either the tip or ring line, an electronic switch, such as a SCR, across the lines and a manually operated momentary hold button which, when operated after picking up the handset of the telephone, switches the electronic switch device to a conducting state and provides a hold current on the lines, the hold current maintained after replacing the handset. The hold condition is indicated by the indicator. An electronic device in one of the lines prevents current flow when the line voltage drops to about 10 volts, when another telephone handset is picked up, switching the electronic switch to a non-conducting state and releasing the hold. A bridge diode arrangement enables operation on either line polarity. Conveniently the indicator is an LED. Lightning and other voltage surges can be restricted by a resistor.

REFERENCES:
patent: 3725600 (1973-04-01), Hutton
patent: 3870831 (1975-03-01), McCarley
patent: 3997734 (1976-12-01), Champan
patent: 4001520 (1977-01-01), Waldman et al.

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