Handsfree telephone instrument using digital dial

Details Handsfree telephone instrument using digital dial Handsfree telephone instrument using digital dial

1982-12-13

1985-01-29

George, Keith E.

179 84VF, 179 90K, H04M 908

Patent

active

044967993

ABSTRACT:
Circuit for controlling the operation of a handsfree or loudspeaking telephone instrument. The circuit includes an integrated circuit dual tone multifrequency (DTMF) generator. When a button of the generator is depressed, and the instrument is in its handsfree mode, power feed to the generator and the speech network is activated. The tone generation circuitry and speech network are thereby connected in parallel with the handsfree hybrid. When the DTMF button is released, power to the speech network is discontinued. Further, when the instrument is in the handsfree mode, and in the non-dialing condition, the confidence tone muting resistance is shunted so that no voice signal attenuation to the handsfree hybrid can occur. The switching is protected against surges both in the handsfree and hookswitch on and off hook conditions and is protected against leakage at the start of the DTMF output.

REFERENCES:
patent: 3833766 (1974-09-01), Eklof et al.
patent: 4087638 (1978-05-01), Hayes et al.
patent: 4315108 (1982-02-01), Hoffman et al.
patent: 4406926 (1983-09-01), Duncan

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