Abstract: Apparatus for detecting the position of a movable member such as the control lever (42) of an audio fader (FIG. 2). A series of light emitting and detecting elements (Q1-Q5) define a plurality of light paths arranged over a distance of D units, and provide a first output indicating which of the light paths are blocked. A shutter (24) includes light-obscuring regions (53, 54, 56) alternating with nonlight-obscuring regions where both the light-obscuring and nonlight-obscuring regions are D units in length. The shutter travels through the light paths so as to affect the output of the light detecting elements. The shutter is coupled to the control lever so that the position of the shutter is dependent upon, and therefore indicates, the position of the movable member.

Abstract: Apparatus is provided for sensing the position of a movable member, such as an audio fader control slider (42), and for controlling an operational characteristic of a controlled device (29), such as the gain of an audio amplifier (34), in accordance therewith. A position detector circuit (26) detects the location of the movable member and provides a first signal indicative thereof. A translation circuit (28) responds to the first signal to provide a second signal representing the value assigned to the position indicated by the first signal. The second signal is applied to the controlled device (29) to control its operational characteristic. The position detection circuit (26) includes elements (24, 36, 38) using radiant energy to detect the location of the movable member.