Abstract: Radiant energy sensors situated in first and second orthogonally positioned rrays may be activated by radiant energy projected thereupon by radiant energy sources spatially separated therefrom, each of the sensors providing a first output level when activated and otherwise providing a second level of output. A control element subject to an operator's manipulation is situated between the sensors of both arrays and their respective activating sources, and is disposed to be movable in two spatial dimensions to selectively shadow sensors of both arrays. The combined outputs of the sensors of the first and second array comprise a control signal in digital form, wherein discrete positions of the control element are represented, the digital control signal being coupled through a digital-to-analog converter to generate analog signals determinative of the motion of a light element on the screen of a cathode ray tube (CRT) display device and functionally related to control element position.