Indicator location determination interface.

摘要

An interface for determining the co-ordinate location of a manually movable stylus (27) on a plane surface (26) comprises a a laser beam source 10 directed onto a rotating mirror scanner (12) behind the surface. The beam is reflected by the scanner along two dihedral mirrors (18, 19) at right angles and is reflected across the front of the surface to retroreflector strips (13, 15) at right angles, and back to a photodetector. The substantially constant photodetector current level is interrupted by the stylus (27) and the angular relationships derived from the timing of the interruptions. From these, the cartesian co-ordinates are determined.