INPUT DEVICES WORKINGCSE212

KEYBOARD BASICS

A keyboard's primary function is to act as an input device. Using a keyboard, a person can type a document, use keystroke shortcuts, access menus, play games and perform a variety of other tasks.

Keyboards can have different keys depending on the manufacturer,

the operating system they're designed for,

and whether they are attached to a desktop computer or part of a laptop.

KEYCAPS

Keycaps are the actual physical keys that you strike with your fingers when typing.

The term "keycap" arises from the fact that these pieces "cap" the actual keyswitches that move during a keystroke

KEYSWITCHES The main job of the keyboard is of course to

translate motion of the fingers into text-based commands sent to the PC.

In order to perform this task, the keyboard must have a way of detecting when keys are pressed. This detection is done through the use of small devices called keyswitches.

Over the years, many different technologies have been used in building the keyswitches used in PC keyboards.

Differences between these technology types have a very important impact on the attributes of the keyboard, especially its durability, cost and "feel".

KEYSWITCH DESIGN ATTRIBUTES

Travel Tactile Feedback Audibility Activation Force "Feel“ Durability Cost

MECHANICAL CONTACT KEYSWITCHES

In some designs, the mechanical keyswitch uses two metal contacts, made of a non-corroding, high-conductance material (the best designs use gold-plated contacts, which of course isn't cheap).

These are separated by a plastic piece that hold them apart, and a spring used to keep the plastic in place and hold the key in its default position. When you press down on the key, the plastic pivots out of the way, and the contacts move towards each other and touch, completing the circuit. When you release the key, the energy stored in the spring reverses the process, opening the circuit as the keycap rises back to its normal place. In other designs, a metal piece is mechanically pushed down to touch contacts on a circuit board to register a keypress.

LIMITATIONS

One problem with this sort of design is that you don't get much in terms of tactile feedback or audibility just by having two metal contacts close a gap and touch each other. As a result, this type of keyswitch usually includes additional hardware to create an audible and tangible "click" as the key is depressed.

ADVANTAGES

The chief advantage of mechanical keyswitches is that they are rather durable, typically rated for tens of millions of activations.

Their main disadvantage is cost: they are expensive to manufacture. They are not common in modern PC keyboards, but many people consider them to be desirable due to their solid feel and strong tactile feedback.

FOAM AND FOIL CONTACT KEYSWITCHES

Like the mechanical contact keyswitch, the foam and foil contact keyswitch design also uses contact to complete a circuit and indicate when a keypress is made. However, it takes a very different approach to creating the contact.

This keyswitch design provides very little in terms of tactile feedback, and typically no audible feedback at all. The foam pads "absorb" the keypresses and this results in a very "spongy" or soft feel.

These keyboards are also not considered by most to be amongst the best available from a practical standpoint. The main durability issue is corrosion and dirt problems that often plague the keyswitches. When either builds up on the foil or the contacts, keypresses become erratic, and problems with "bounce" or keys that won't register begin to occur.

RUBBER DOME (CARBON-CONTACT) KEYSWITCHES

The rubber-dome keyswitch design uses the same basic principle of operation as the foam and foil keyswitch, but significantly improves upon the latter's weaknesses by using better materials to make and break contact.

As with the foam and foil design, a circuit board with pairs of electrical contacts is used. In this technology, however, instead of a plunger pushing a foam pad onto the contacts, each keyswitch is fitted with a rubber dome, or hood, which is placed open-end down on the surface of the circuit board, the way you might place a bottle cap on a table with the flat surface up. On the underside of the rubber dome, at the top, is a small pad or "button" of carbon.

When the plunger is pressed by the keycap, the rubber dome is pushed down until it passes its "bending point", at which point it temporarily "collapses". When this happens, the carbon button connects the pads on the circuit board and the circuit is closed, registering the keypress. When the plunger is released, the rubber naturally reforms itself, forcing the key back to its normal position.

In terms of feel, most typists find rubber dome designs good, or at least acceptable. They don't have as strong a feel or loud a sound as the purely mechanical or capacitive designs

When it comes to durability, this technology is also fairly "middle of the pack". There are still occasionally corrosion and dirt problems, but less so than with foam and foil designs, since the small carbon buttons are less susceptible to contamination.

MEMBRANE CONTACT KEYSWITCHES

The membrane contact keyswitch is a variant of the rubber dome design and works in a rather similar way. The basic mechanism is the same: contact pairs on a circuit board, and rubberized boots or "dimples" with a carbon button underneath. Press down the key and the rubber deforms, the carbon touches the contacts and a keystroke is sensed.

The big difference here is that individual keycaps and plastic plungers are replaced with a thin membrane that fits over the rubber domes. There may not even be separate rubber domes, just molded "dimples" for each key, the carbon buttons in each dimple. The user presses directly on the membrane to collapse the domes and create contact with the printed circuit board. Travel is very small with this design, since there is no keycap and no plunger.

This technology has some advantages over the others, however. One is that it is quite cheap to make, because you eliminate a large percentage of the parts from a typical keyboard design. Another is that the solid membrane seals dirt and contamination out of the internal workings of the keyboard. For this reason, this technology is sometimes used in industrial applications

KEYBOARD SWITCHES

Keyboards use a variety of switch technologiesCapacitive switches

Capacitive switches are considered to be non-mechanical because they do not physically complete a circuit like most other keyboard technologies. Instead, current constantly flows through all parts of the key matrix.

Each key is spring-loaded and has a tiny plate attached to the bottom of it. When you press a key, it moves this plate closer to the plate below it. As the two plates move closer together, the amount of current flowing through the matrix changes.

A CAPACITIVE BUCKLING SPRING KEYSWITCH.

The processor detects the change and interprets it as a key press for that location. Capacitive switch keyboards are expensive, but they have a longer life than any other keyboard. Also, they do not have problems with bounce since the two surfaces never come into actual contact.

BASIC WORKING

A keyboard is a lot like a miniature computer. It has its own processor and circuitry that carries information to and from that processor. A large part of this circuitry makes up the key matrix.

The key matrix is a grid of circuits underneath the keys. In all keyboards (except for capacitive models, which we'll discuss in the next section), each circuit is broken at a point below each key.

When you press a key, it presses a switch, completing the circuit and allowing a tiny amount of current to flow through.

The mechanical action of the switch causes some vibration, called bounce, which the processor filters out. If you press and hold a key, the processor recognizes it as the equivalent of pressing a key repeatedly.

When the processor finds a circuit that is closed, it compares the location of that circuit on the key matrix to the character map in its read-only memory (ROM).

A character map is basically a comparison chart or lookup table. It tells the processor the position of each key in the matrix and what each keystroke or combination of keystrokes represents.

For example, the character map lets the processor know that pressing the a key by itself corresponds to a small letter "a," but the Shift and a keys pressed together correspond to a capital "A."

Whether it's through a cable or wireless, the signal from the keyboard is monitored by the computer's keyboard controller. This is an integrated circuit (IC) that processes all of the data that comes from the keyboard and forwards it to the operating system. When the operating system (OS) is notified that there is data from the keyboard, it checks to see if the keyboard data is a system level command. A good example of this is Ctrl-Alt-Delete on a Windows computer, which reboots the system. Then, the OS passes the keyboard data on to the current application.

The application determines whether the keyboard data is a command, like Alt-f, which opens the File menu in a Windows application.

If the data is not a command, the application accepts it as content, which can be anything from typing a document to entering a URL to performing a calculation. If the current application does not accept keyboard data, it simply ignores the information. This whole process, from pressing the key to entering content into an application, happens almost instantaneously.

In fact, the keyboard has within it small versions of several components you find within the PC as a whole. It has its own microprocessor, which "runs the show" so to speak. (This is of course a tiny CPU like the 8048, not a full-fledged CPU as the main PC hardware uses.) There is also some read-only memory (ROM) that runs this small processor, similar to the system BIOS code on the motherboard. Programmable keyboards also contain some EEPROM memory to hold programming information

KEYBOARD CABLE

KEYBOARD AND MOUSE CONNECTORS.

KEYBOARD POWER

To simplify the operation of the PC, the keyboard was designed from the start to take its power from the system--more specifically, from the motherboard. Thus, two of the wires that run through the keyboard cable carry power and ground signals from the motherboard to the keyboard. This is usually a +5 volt signal, the standard for many devices within the PC.

Most keyboards have between 80 and 110 keys, including:

Typing keys A numeric keypad Function keys Control keys

TYPING KEYS

The typing keys include the letters of the alphabet, generally laid out in the same pattern used for typewriters.

According to legend, this layout, known as QWERTY for its first six letters, helped keep mechanical typewriters' metal arms from colliding and jamming as people typed.

Some people question this story -- whether it's true or not, the QWERTY pattern had long been a standard by the time computer keyboards came around. 

Keyboards can also use a variety of other typing key arrangements. The most widely known is Dvorak, named for its creator, August Dvorak. The Dvorak layout places all of the vowels on the left side of the keyboard and the most common consonants on the right. The most commonly used letters are all found along the home row. The home row is the main row where you place your fingers when you begin typing. People who prefer the Dvorak layout say it increases their typing speed and reduces fatigue. Other layouts include ABCDE, XPeRT, QWERTZ and AZERTY. Each is named for the first keys in the pattern. The QWERTZ and AZERTY arrangements are commonly used in Europe.

NUMERIC KEYPAD

The numeric keypad is a more recent addition to the computer keyboard. As the use of computers in business environments increased, so did the need for speedy data entry. Since a large part of the data was numbers, a set of 17 keys, arranged in the same configuration found on adding machines and calculators, was added to the keyboard.

FUNCTION AND CONTROL KEYS

In 1986, IBM further extended the basic keyboard with the addition of function and control keys. Applications and operating systems can assign specific commands to the function keys. Control keys provide cursor and screen control. Four arrow keys arranged in an inverted T formation between the typing keys and numeric keypad move the cursor on the screen in small increments.

Other common control keys include: Home End Insert Delete Page Up Page Down Control (Ctrl) Alternate (Alt) Escape (Esc)

Many keyboards connect to the computer through a cable with a PS/2 or USB (Universal Serial Bus) connector.

Laptops use internal connectors. Regardless of which type of connector is used, the cable must carry power to the keyboard, and it must carry signals from the keyboard back to the computer.

THE PRIMARY KEYBOARD TYPES ARE AS FOLLOWS:

101-key Enhanced keyboard 104-key Windows keyboard 83-key PC and XT keyboard (obsolete) 84-key AT keyboard (obsolete)

Read the docx file uploaded for that

TO USE A KEYBOARD CONNECTED VIA THE USB PORT, YOU MUST MEET THREE REQUIREMENTS:

Have a USB port in the system Run Microsoft Windows 98, Windows Me,

Windows 2000, or Windows XP (all of which include USB keyboard drivers)

Have a system chipset and BIOS that feature USB Legacy support

USB Legacy support means your motherboard has a chipset and ROM BIOS drivers that enable a USB keyboard to be used outside the Windows GUI environment. When a system has USB Legacy support enabled, a USB keyboard can be used with MS-DOS (for configuring the system BIOS) when using a command prompt within Windows or when installing Windows on the system for the first time. If USB Legacy support is not enabled on the system, a USB keyboard will function only when Windows is running. Most recent systems include USB Legacy support, although it might be disabled by default in the system BIOS.

KEYBOARD TROUBLESHOOTING AND REPAIR

Keyboard errors are usually caused by two simple problems. Other more difficult, intermittent problems can arise, but they are much less common. The most frequent problems are as follows:

Defective cables Stuck keys

Desassembly & cleaning

POINTING DEVICES

When the mouse hit the scene -- attached to the Mac, it was an immediate success. There is something about it that is completely natural.

In the PC world, mice took longer to gain ground, mainly because of a lack of support in the operating system.

Once Windows 3.1 made Graphical User Interfaces (GUIs) a standard, the mouse became the PC-human interface of choice very quickly.

INSIDE A MOUSE The main goal of any mouse is to translate

the motion of your hand into signals that the computer can use. Let's take a look inside a track-ball mouse to see how it works:

A ball inside the mouse touches the desktop and rolls when the mouse moves.

The underside of the mouse's logic board: The exposed portion of the ball touches the desktop.

Two rollers inside the mouse touch the ball. One of the rollers is oriented so that it detects motion in the X direction, and the other is oriented 90 degrees to the first roller so it detects motion in the Y direction. When the ball rotates, one or both of these rollers rotate as well. The following image shows the two white rollers on this mouse:

CONCEPT OF ENCODER WHEEL

The rollers that touch the ball and detect X and Y motion

A TYPICAL OPTICAL ENCODING DISK: THIS DISK HAS 36 HOLES AROUND ITS OUTER EDGE.

The rollers each connect to a shaft, and the shaft spins a disk with holes in it. When a roller rolls, its shaft and disk spin. The following image shows the disk:

On either side of the disk there is an infrared LED and an infrared sensor. The holes in the disk break the beam of light coming from the LED so that the infrared sensor sees pulses of light. The rate of the pulsing is directly related to the speed of the mouse and the distance it travels.

An on-board processor chip reads the pulses from the infrared sensors and turns them into binary data that the computer can understand. The chip sends the binary data to the computer through the mouse's cord.

In this optomechanical arrangement, the disk moves mechanically, and an optical system counts pulses of light. On this mouse, the ball is 21 mm in diameter. The roller is 7 mm in diameter. The encoding disk has 36 holes. So if the mouse moves 25.4 mm (1 inch), the encoder chip detects 41 pulses of light.

OPTICAL MICE

Developed by Agilent Technologies and introduced to the world in late 1999, the optical mouse actually uses a tiny camera to take thousands of pictures every second.

Able to work on almost any surface without a mouse pad, most optical mice use a small, red light-emitting diode (LED) that bounces light off that surface onto a complimentary metal-oxide semiconductor (CMOS) sensor.

In addition to LEDs, a recent innovation are laser-based optical mice that detect more surface details compared to LED technology. This results in the ability to use a laser-based optical mouse on even more surfaces than an LED mouse.

HERE'S HOW THE SENSOR AND OTHER PARTS OF AN OPTICAL MOUSE WORK TOGETHER:

The CMOS sensor sends each image to a digital signal processor (DSP) for analysis.

The DSP detects patterns in the images and examines how the patterns have moved since the previous image.

Based on the change in patterns over a sequence of images, the DSP determines how far the mouse has moved and sends the corresponding coordinates to the computer.

The computer moves the cursor on the screen based on the coordinates received from the mouse. This happens hundreds of times each second, making the cursor appear to move very smoothly.

OPTICAL MICE HAVE SEVERAL BENEFITS OVER TRACK-BALL MICE:

No moving parts means less wear and a lower chance of failure.

There's no way for dirt to get inside the mouse and interfere with the tracking sensors.

Increased tracking resolution means a smoother response.

They don't require a special surface, such as a mouse pad.

All optical mice have a resolution of at least 400dpi and at least one sensor. However, for better performance, some optical mice have improved on these basic features, as listed

After the mouse is connected to your computer, it communicates with your system through the use of a device driver, which can be loaded explicitly or built into the operating system software. For example, no separate drivers are necessary to use a mouse with Windows or OS/2, but using the mouse with most DOS-based programs requires a separate driver to be loaded from the CONFIG.SYS or AUTOEXEC.BAT file. Regardless of whether it is built in, the driver translates the electrical signals sent from the mouse into positional information and indicates the status of the buttons.

POINTING DEVICE INTERFACE TYPES

The connector used to attach your mouse to the system depends on the type of interface you are using. Three main interfaces are used for mouse connections, with a fourth option you also occasionally might encounter. Mice are most commonly connected to your computer through the following three interfaces:

Serial interface Dedicated motherboard (PS/2) mouse port USB port

SERIAL

A popular method of connecting a mouse to older PCs is through the standard serial interface. As with other serial devices, the connector on the end of the mouse cable is typically a 9-pin male connector; some very old mice used a 25-pin male connector. Only a couple of pins in the DB-9 or DB-25 connector are used for communications between the mouse and the device driver, but the mouse connector typically has all 9 or 25 pins present.

MOTHERBOARD MOUSE PORT (PS/2)

Most computers include a dedicated mouse port built into the motherboard. This practice was introduced by IBM with the PS/2 systems in 1987, so this interface is often referred to as a PS/2 mouse interface. This term does not imply that such a mouse can work only with a PS/2; instead, it means the mouse can connect to any system that has a dedicated mouse port on the motherboard.

HYBRID MICE

Hybrid mice are those designed to plug into two types of ports. Although a few low-cost mice sold at retail are designed to plug into either the serial port or the PS/2 port, most mice on the retail market today are designed to plug into either the PS/2 port or the USB port. These combination mice are more flexible than the mice typically bundled with systems, which are designed to work only with the PS/2 or USB port to which they attach.

USB

MOUSE TROUBLESHOOTING

Cleaning Your Mouse Interrupt Conflicts Interrupts are internal signals used by your

computer to indicate when something needs to happen. With a mouse, an interrupt is used whenever the mouse has information to send to the mouse driver. If a conflict occurs and the same interrupt used by the mouse is used by a different device, the mouse will not work properly—if at all.

Interrupt conflicts caused by mice can occur when a serial or PS/2 mouse is used, but not when a USB mouse is used. Mouse ports built in to modern motherboards are almost always set to IRQ12. If your system has a motherboard mouse port, be sure you don't set any other adapter cards to IRQ12; otherwise, a conflict will result.

The best way around these interrupt conflicts is to make sure no two devices use the same interrupt. Serial port adapters are available for adding COM3 and COM4 serial ports that do not share the interrupts used by COM1 and COM2. These boards enable the new COM ports to use other normally available interrupts, such as IRQs 10, 11, 12, 15, and 5.

DRIVER SOFTWARE

Most mice and other pointing devices in use today emulate a Microsoft mouse, enabling you to have basic two-button plus scrolling functions with current versions of Windows without loading any special drivers. However, if your mouse has additional buttons or other special features, you will need to install device-specific drivers available from the mouse vendor.

If you plan to use the mouse from a Windows 9x/Me command prompt or with DOS, you must load the driver manually.

SCROLL WHEELS

Late in 1996, Microsoft introduced the IntelliMouse, which differed from standard Microsoft mice by adding a small gray wheel between the mouse buttons. This was the first scrolling mouse, and since then, Logitech, IBM, and virtually all other mouse vendors have made scroll wheels or similar devices standard across almost all models, including OEM mice bundled with computer systems.

The wheel has two main functions. The primary function is to act as a scrolling device, enabling you to scroll through documents or Web pages by manipulating the wheel with your index finger. The wheel also functions as a third mouse button when you press it.

TRACKPOINT II/III/IV

IBM studies conducted by Selker found that the act of removing your hand from the keyboard to reach for a mouse and replacing the hand on the keyboard takes approximately 1.75 seconds. If you type 60wpm, that can equal nearly two lost words per minute, not including the time lost while you regain your train of thought. Almost all this time can be saved each time you use TrackPoint to move the pointer or make a selection (click or double-click). The combination of the buttons and the positioning knob also enable you to perform drag-and-drop functions easily.

IBM's research also found that people can get up to 20% more work accomplished using the TrackPoint instead of a mouse, especially when the application involves a mix of typing and pointing activities, such as with word processing, spreadsheets, and other typical office applications. In usability tests with the TrackPoint III, IBM gave a group of desktop computer users a TrackPoint and a traditional mouse. After two weeks, 80% of the users had unplugged their mice and switched solely to the TrackPoint device.

MOUSE AND POINTING STICK ALTERNATIVES

Because of Windows, many users spend at least as much time moving pointers around the screen as they do in typing, making pointing device choices very important. In addition to the mouse and the pointing stick choices discussed earlier in this chapter, several other popular pointing devices are available, including

Track pads, such as the Cirque GlidePoint Trackballs from many vendors Upright mice, such as the 3M Renaissance

Mouse

GLIDEPOINT/TOUCH PAD

Cirque originated the touch pad (also called a track pad) pointing device in 1994. Cirque refers to its technology as the GlidePoint and has licensed the technology to other vendors such as Alps Electric, which also uses the term Glidepoint for its touch pads. The GlidePoint uses a flat, square pad that senses finger position through body capacitance. This is similar to the capacitance-sensitive elevator button controls you sometimes encounter in office buildings or hotels.