PC Hardware A Beginner’s Guide

(^466) PC Hardware: A Beginner’s Guide
 Optical encoding disk As the ball rolls, the rollers turn the shafts that spin
the optical encoding disks. The optical encoding disk has 36 holes along its
outside edge.
 Infrared LED and sensor On one side of each optical encoding disk is a
light-emitting diode (LED) that shines an infrared light beam on the disk. On
the other side of the disk is a light-sensitive transistor that serves as an infrared
sensor. As the disk turns, the solid areas between the holes on the disk break
the LED’s infrared beam and the infrared sensor sees pulses of light. The rate
and duration of the light pulses indicate the speed and distance of the mouse’s
travel. Figure 18-20 illustrates the placement of the infrared LED and sensor to
the optical encoding disk.
 Processor The mouse has a processor that reads the pulses sent from the
infrared sensors and converts them into binary data, which is sent to the PC’s
interface over the mouse’s connecting cord.
 Buttons The mouse also has one, two, three, or more buttons (two is the most
common number of buttons on PC mice) that are connected to small switches
that also connect to the mouse’s processor. As the user clicks the buttons to
select an object on the screen or start a program or applet, the processor converts
the clicks into binary data that is sent to the PC. Windows systems use two-button
mice; Macintosh systems have gotten by very nicely with a single mouse button;
and UNIX and Linux systems have functions that require the use of a third
mouse button. Mice that have buttons on to pas well as on the side and
elsewhere require special software device drivers to enable the function of
these buttons.
Figure 18-20. The optical encoding disk has 36 holes, like the four shown, through which an
infrared beam is sensed