Electroacoustical telephone adapter for hands-free telephone

Abstract From the Canadian patent

A telephone adapter for hands-free telephony adapted, for use with a telephone handset having structure including an earpiece, and a microphone handset. The adapter comprises a transmit signal path comprising, in series a microphone, an amplifier, a switch and a transducer; and a receive signal path having amplifier for sound energy from the earpiece. The receive path comprises, in series, a coupler, an amplifier a switch, and a speaker. A bias maintains the transmit path in an active state when no signals are present; and a circuit interrupts the circuit paths in a complementary manner.