Patent ID: 7902448

Claim:
An operation position sensor device for an electronic musical instrument, comprising: an operation member; a light emitting section; a photodetecting section; a light amount controlling member that is placed in an optical path between the light emitting section and the photodetecting section, wherein the light amount controlling member includes a transmission film having a plurality of zones formed in the transmission film, wherein the zones provide different transparencies that change as an operation position of the operation member changes, wherein the zones provide a plurality of transparencies that emit light, and wherein the transmission film controls the amount of light inputted from the light emitting section to the photodetecting section according to the operation position of the operation member; and an operation position sensor section that detects the operation position of the operation member based on the amount of light received by the photodetecting section, determines that the operation position of the operation member has shifted from one of operation position zones to adjacent one of the operation position zones when the amount of light detected by the photodetecting section changes, and determines to which one of adjacent ones of operation position zones the operation position has shifted from the one of operation position zones depending on whether the amount of light has increased or decreased.