Abstract: An apparatus for providing a control signal utilizes a liquid crystal panel and means for transiently forming transparent windows therein. There is a source of electromagnetic radiation (EMR) adjacent the panel and positioned to pass EMR through transiently open windows. There is an EMR detector positioned adjacent the source and a defined EMR path between the source and detector which path is formed in response to a transiently open window and includes an area for the positioning of an object to occlude the EMR radiation passing between the source and detector. The path also includes a reflector which directs EMR from the source back in the same general direction to the detector. There is a timing and logic circuit correlating the opening of the transient windows and the detection of EMR at said detector to provide a control signal.

Abstract: An apparatus for providing a control signal includes a liquid crystal panel with means for transiently forming transparent windows therein. There is a source of electromagnetic radiation (EMR) adjacent one side of the panel and positioned to pass EMR through a first set of transiently open windows adjacent thereto. There is an EMR detector positioned adjacent an opposite side of the panel and positioned to detect EMR from the source which has passed through one or more of the first set of transiently open windows and which has also passed through one or more of a second set of transiently open windows positioned adjacent the detector. There is a timing and logic circuit which correlates the opening of windows in the first set and in the second set whereby an EMR occluding object may be located relative to mutually perpendicular axes, one of which is parallel to both the first and second set of transiently open windows, the location of said occluding object providing a control signal representative thereof.