3.6. Mouse and Trackball   

3.6.1. Mouse   

Hand held device with rollers on its base. Moving mouse -> rollers turn -> potentiometer turns or pulse train sent out.

 Motion -> digital values -> direction and distance.

Since can pick up mouse and replace without changing cursor position

on screen, mouse reports relative position i.e.  dx, dy therefore

computer must maintain a "current mouse position" which is

incremented/decremented by mouse movement.

Very good feed back mechanism since cursor moves quickly

and accurately. However, very fine control is not always possible since

positioning motor control is not good.

 MOUSE also has keys/buttons for selection.

     


    
    Fig. 3.8 : A left and a right handed three buttoned mouse

     


    
                 Fig. 3.9 : A two buttoned mouse

3.6.2. Trackball   

A spherical ball set in a housing along with buttons. The ball turns easily ( and continuously if need be) in any direction. Either potentiometers are changed by the balls movement (analogue output to the computer) or the movement sends a pulse train to the computer (digital output).

Therefore hand movement on the trackball -> used to change position of a cursor on screen.