Rounding the mouse ..........................................................................
A mouseis a rounded block of plastic with a sensor on the bottom that trans-
lates movement across a mouse pad or a desktop into movement on the
screen. For Windows-based systems, the mouse has at least two buttons; the
left button is generally used to select an item or execute a command, while
the right button brings up context-sensitive menus. You also see mice that
add a central scroll wheel that can be used by itself or in conjunction with
the left or right button to move the screen or menus up and down. Mice can
be of either mechanical or optical design. A mechanical mouse’s insides are
described in the preceding section.A mechanical mousehas a small rubber or plastic ball on its bottom or top.
As a mouse moves across a surface (or as your fingers move a trackball’s
ball), the ball turns small rollers or shafts, which cause metallic contacts or
brushes to sweep across a segmented conductor. As the brushes make and
break electrical contact, a microprocessor counts the number of contacts
and the time interval between them to determine the direction and speed of
movement. In most designs, there are two rollers or shafts, mounted at a 90-
degree angle; if both rollers are moving, the mouse is smart enough to figure
out that it is being moved on an angle. The end result is a signal sent to the
computer’s CPU for action.An optical mousehas no moving parts. Instead they employ an electronic
sensor that uses a special mouse pad with a highly reflective surface and
finely etched lines to determine movement and create signals. An alternate
design uses a high-intensity light-emitting diode (LED)that illuminates the
lines on a pad. In theory, an optical mouse is capable of discerning extremely
fine movement — as fine a resolution as^1 ⁄ 2000 of an inch, which is 2 to 10 times
as delicate as a mechanical device — and many of the latest designs no
longer require the use of a special optical pad.Perched in between are optomechanical mice,in which a moving ball turns
rollers with slots or perforations; an internal LED shines through the open-
ings and an optical sensor detects the pulses and converts them into a signal.
The advantage of optomechanical devices is high precision without the need
for a specialized mouse pad.Keeping your eye on the trackball ...................................................
Think of a trackballas a mouse turned upside down. You use your fingers to
rotate an oversized ball that uses sensors that translate that movement into
signals to the computer. Trackballs can use mechanical or optical sensors. A
mechanical trackballrolls against a set of rotary switches that sense up, down,
or side-to-side movement. An optical trackballmoves in front of a photoelectric
or photoreflective sensor that reads the movement of a pattern on the ball. The
optical trackball may be slightly more sensitive than a mechanical equivalent.174 Part III: Laying Hands on the Major Parts