| 摘要 |
A combination control knob and encoder drum unit, which has a number of indexing indentations corresponding to the number of desired stable positions thereof, is sized to pass through an opening in a control panel behind which is mounted a drum-receiving housing. The drum has groups of light-transparent areas each for providing a pattern of light identifying a different signal channel. The housing has a light source which passes within the drum when it is fully mounted within the housing, and a bearing adapted to receive a shaft extending from the combination knob and encoder unit. A spring loaded drum holding projection is urged toward and enters an adjacent encoder unit indentation. The housing has photocell means at a light pattern reading station to which the various groups of light-transmitting areas on the drum can be individually brought. To increase the number of channel selection positions, a combination knob and encoder unit is merely replaced by another similar unit with a different number of groups of light-transparent areas and indexing indentations.
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