Tracker-Ball For Atari St

48 TRACKER-BALL FOR ATARI ST ENE by A. Schaffert The use of a mouse for controlling a computer has become common practice. There may be a problem, though: space. It often happens that there is not enough room to move the mouse when the desk is littered with print-outs, pencils, notepads, books, diskettes and the odd cup of coffee. These space problems can be solved by the use of a tracker-ball, which is simply a mouse turned upside down. The operation of a tracker-ball is basically identical to that of a mouse, but the ball movement is achieved via direct operation by the hand, rather than via the desk surface, or, if this is too smooth or slippery, the mouse pad. The principle of operation of the tracker-ball is clearly illustrated by the drawing in Fig. 1. Two spindles, fitted at right angles, drive encoder discs. Two opto- couplers are fitted for each disc, to translate the ball rotation into a logic signal. A small auxiliary spindle (visible in the photograph of Fig. 5) is pro...