Hardware Reference
In-Depth Information
physical movement. Fast movement is especially desirable in some games, which is why so-called
“gaming” mice have extremely high DPI ratings that can usually be configured via software included
with the mouse. Some mice have switches that allow you to change the DPI rating on the fly, since you
may want it instantly higher or lower at different times during gameplay.
Ball-Type Mice
The bottom of the mouse housing is where the detection mechanisms or electronics are located. On
traditional mice, the bottom of the housing contains a small, rubber ball that rolls as you move the
mouse across the tabletop. The movements of this rubber ball are translated into electrical signals
transmitted to the computer across the cable.
Internally, a ball-driven mouse is simple. The ball usually rests against two rollers: one for
translating the x-axis movement and the other for translating the y-axis movement. These rollers are
typically connected to small disks with shutters that alternately block and allow the passage of light.
Small optical sensors detect movement of the wheels by watching an internal IR light blink on and off
as the shutter wheel rotates and “chops” the light. These blinks are translated into movement along the
axes. Ball type mice are considered obsolete today, although many are still in use.
Optical Mice
The other major method of motion detection is optical. Some of the early mice made by Mouse
Systems and a few other vendors used a sensor that required a special grid-marked pad. Although
these mice were accurate, the need to use them with a pad caused them to fall out of favor.
Microsoft's IntelliMouse Explorer pioneered the rebirth of optical mice. The IntelliMouse Explorer
and the other new-style optical mice from Logitech and other vendors use optical technology to detect
movement, and they have no moving parts of their own (except for the scroll wheel and buttons on
top). Today's optical mice need no pad; they can work on virtually any surface. This is done by
upgrading the optical sensor from the simple type used in older optical mice to a more advanced CCD
(charge coupled device). This essentially is a crude version of a video camera sensor that detects
movement by seeing the surface move under the mouse. An LED or diode laser provides light for the
sensor. Many mice now incorporate IR laser technology sensors, which increase the resolution of the
sensor, allowing for improved tracking on glossy or transparent surfaces.
The IntelliMouse Explorer revolutionized the mouse industry; first Logitech, and then virtually all
other mouse makers, including both retail and OEM suppliers, have moved to optical mice for most of
their product lines, offering a variety of optical mice in most price ranges.
Figure 15.10
shows the
essential features of a typical optical mouse.
