Variable attenuator apparatus

Claim 1

A variable attenuator apparatus comprising: a housing; a rotatable shaft extending inwardly of the housing; first and second spaced-apart, stationary insulating substrate elements supported within the housing, one of said elements including a shaft-receiving aperture through which the rotatable shaft extends, each substrate element supporting a pair of first and second terminals, the first and second terminals of one pair being connected respectively to the first and second terminals of the other pair; a contact brush carrier disposed between the substrate elements and mounted on the rotatable shaft for rotation therewith; first and second arcuate resistance tracks and first and second collector tracks supported respectively by the first and second substrate elements; a pair of fixed resistors supported by the second substrate element and connected respectively between one end of the second arcuate resistance track and the first and second terminals of the second substrate element; the terminals of the first substrate element being directly connected to one end of the first arcuate resistance track and to the collector track, respectively; a pair of spring-loaded contact brushes mounted on opposite faces of the contact brush carrier for rotation therewith, each contact brush being spring-biased into sliding bridging engagement with the arcuate resistance track and collector track of the respective substrate element to define therewith a variable resistor, said variable resistors varying in opposite senses upon rotation of the shaft; a first terminal connection to said interconnected first terminals of the substrate elements; a second terminal connection to said interconnected second terminals of the substrate elements; and a third terminal connection to said second collector track.