INPUT DEVICES
Keyboard
The keyboard: most important device in a computer besides the processor. Since
the invention of the first few PCs, the keyboard has existed, and through
time the keyboard has evolved into many different looks and types. The keyboard
of today contains 109 keys in total not including extra keys such as shutdown,
suspend, power on or other special functions. Keyboards used to connect to
the computer via a large round 6-pin port called the AT, but today, as the
mouse, the keyboard connects to the computer via the PS2 port. Some new versions
of keyboards also connect to the USB(Universal Serial Bus) port, but these
are less common. Although it may look just like a keyboard, do not be fooled
that all keyboards are the same! Some keyboards are able to take in many keys
at a time while others can only accept one key at a time. This can be vital
when playing games (strafing/walking at the same time). The keyboards of today
also vary in other ways: Some are plug and play while others are not. However,
keyboards can also be called basically "similar" as all are automatically
detected at startup and, in many computers, do not need drivers to install,
as these drivers come with most operating systems such as Windows 95 or Windows
2000.
Mouse
Mouse (plural mice) entered the world of computers since 1985 to 1990, and has been vital in pushing computers into the main consumer market. It made everything easier for users: Clicking, for some, was and is faster than typing, and you can access files and edit them easier with mice. Mice work by sending coordinates of the amount the user moves to the computer, which then calculates where the mouse cursor is on the screen. Mice connect to computers by the serial and PS2 port. Like almost all other components, mice too can differ in quality and type. Some mice have a scrolling button in the middle for surfing the Internet and scrolling easier; others have two keys instead of three. Also, mouserates, or the rate at which the mouse reports are different with each mouse. Mouserates is measured in herz (hz), and the average or acceptable mouserate is about 50. Low mouserates will result in the cursor movement becoming jerky.
TouchPad
The most common pointing device on new laptop computers
is the touchpad, a small black or gray rectangle typically located below the
keyboard. Moving a finger across the pad causes the cursor to move similarly
on the screen. Touchpads began appearing on laptops only about four years
ago, but they have already displaced built-in trackballs as the standard pointing
device on portable computers. Today more than two thirds of all laptops sold
come equipped with touchpads. Touchpads offer better ergonomics for many people,
such as those afflicted with arthritis. And because the devices are completely
sealed and have no moving parts, dirt or grit cannot get inside them, making
them more suited to dusty or corrosive environments, such as workshops, factory
floors and garages. The most popular type of touchpad is capacitance-based.
It measures changes in capacitance as the user's finger alters the imperceptibly
minute electric fields above the pad.
Finding the finger involves shifting two patterns of voltage pulses. To check
the capacitance at every single point at which the electrodes cross would
take too much time, resulting in sluggish response to finger movement. Instead
two patterns (left and right diagrams) of positive (orange) and negative (green)
pulses are applied to the electrodes and the electric charge from the mutual
capacitance is measured. Calculations involving the ratio of the total charge
measured for each pattern locate the finger in relation to the boundary between
regions of positive and negative pulses. The two patterns must shift as the
finger moves to keep this boundary near the center of the finger. In this
illustration the patterns are shown for only the set of vertical parallel
electrodes; in operation, the same shifting patterns are executed on the other
(orthogonal) set of electrodes, enabling two-dimensional tracking of finger
movements at speeds up to 100 centimeters (40 inches) a second.
|
Electrodes are on two layers, oriented orthogonally to each other, and separated by a thin sheet of fiberglass.The fiberglass acts as an insulator, or "dielectric." An electric field is set up when a voltage pulse is applied between an upper and a lower electrode, in effect turning the two electrodes, the intervening dielectric fiberglass material and even the surrounding air into a capacitor. This electric field is modified by the presence of a finger. The distortion in the field caused by the finger results in a slightly lower mutual capacitance between the two electrodes. This decrease reduces the amount of electric charge coupled to the bottom electrode. |
 |
.......................................................................................
