Telephone-activated audio control circuit
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United States of America Patent
Stats
-
Jun 21, 1983
Grant Date -
N/A
app pub date -
Dec 18, 1980
filing date -
Dec 18, 1980
priority date (Note) -
Expired
status (Latency Note)
Importance
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.
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