A sensor including lenses, light emitters, each emitter projecting light out of a lens in a particular emission direction along a detection plane, light detectors, each detector detecting maximum light intensity when light enters a lens at a particular detection angle, a table of hotspots, each hotspot corresponding to an emitter-detector pair, the hotspot being a two-dimensional location in the detection plane along the emission direction of the emitter of the pair where projected light reflected by an object placed at that location, enters the lens for the detector of the pair at the detection angle of the detector, and a processor receiving outputs from the detectors corresponding to detected amounts of projected light reflected by an object in the detection plane, and calculating a two-dimensional location of the object in the detection plane based on the received outputs and based on hotspots for synchronously activated emitter-detector pairs.