Disclosed examples include optical and capacitive position detection systems and user interface control apparatus to detect relative positions of a stationary first structure and a movable second structure. The optical system includes pairs of optical source and sensor devices spaced along a first direction on the first structure and a reflector extending along the first direction on the second structure to selectively reflect light from one of the optical sources to the corresponding optical sensor of a given pair when the reflector is proximate the given pair. The capacitive sensing system includes capacitor plate structures on the first structure and a conductive structure on the second structure to move along the first direction to selectively modify a capacitance of a given group of two or more of the plate structures. The detection system also includes an interface circuit to provide a position signal representing the relative position of the first and second structures according to signals from the optical sensors and the capacitor plate structures.