Method and apparatus for retrofitting a standard coin operated t

Details Method and apparatus for retrofitting a standard coin operated t Method and apparatus for retrofitting a standard coin operated t

1989-09-15

1991-01-15

Schreyer, Stafford D.

Telephonic communications

Diagnostic testing, malfunction indication, or electrical...

Testing of subscriber loop or terminal

379146, 379155, 381112, H04M 1702

Patent

active

049859102

ABSTRACT:
A method and apparatus to enable a low power telephone controller to operate with either a carbon microphone or a dynamid microphone is described. A jumper in a preamplifier and filter circuit is preset to accommodate the audio transfer characteristics of one or the other type of microphones. For either microphone, a small DC current of less than 500 .mu.A is used to sense the presence of either type microphone and serves the dual role of biasing the carbon microphone to the appropriate level to be amplified so that the input to an audio circuit in the controller us very nearly the same for either microphone. The audio circuit then processes and dynamically balances the signal to the telephone line, where it is output.

REFERENCES:
patent: 3132207 (1964-05-01), McCalla

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