Arnold, White & Durkee
Universal telephone handset interface
 An apparatus 10 is employed for interfacing a telephone handset 18 to a telephone network. Typically, a telephone handset has one of a variety of different microphones disposed therein, such as carbon, electret, etc., where each type of microphone has a different output level and impedance. Conversely, the telephone network with which the microphone is to be interfaced has a preselected input impedance and signal requirement intended to match only one type of microphone. The apparatus 10 includes a plurality of switches 82, 84, 86, 88 and resistors 90, 92, 94 that are manually switchable into the circuit either separately or in combination to match the output impedance and signal level of the microphone with the input impedance and signal level of the telephone network. Alternatively, in a second embodiment of the instant apparatus, a variable resistor is employed to match the output impedance and signal level of the microphone with the input impedance and signal level of the telephone network. 
Plantronics, Inc.
H H
H04M H04M
inventional inventional
Rickey R. David O.
Walker Hanon