Telephone-activated audio control circuit

Details Telephone-activated audio control circuit Telephone-activated audio control circuit

1980-12-18

1983-06-21

Rubinson, G. Z.

179 18FA, H04M 1100

Patent

active

043895433

ABSTRACT:
The inputs of an operational amplifier are connected across a telephone line and bridged by a capacitor. The output of the operational amplifier drives the coil of a relay via an intermediate amplifier. The relay is of the make-before-break type, and is interposed between an audio source, audio speakers, and dummy load resistors. When the voltage across the telephone line indicates an on-hook condition for a telephone, the audio source is connected to the speakers through the relay. When the voltage across the telephone lines indicates an off-hook condition of the telephone, the audio source is connected to the dummy resistors and disconnected from the speakers and is thereby muted, enabling telephone conversation to take place.

REFERENCES:
patent: 3523823 (1970-10-01), Ellis
patent: 3622709 (1971-11-01), Tjaden
patent: 4079201 (1978-03-01), Scott et al.
patent: 4079208 (1978-03-01), Rogers et al.
patent: 4220825 (1980-09-01), Fahey
patent: 4323734 (1982-04-01), Kimzey
patent: 4338492 (1982-07-01), Snopko

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