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| Sunday, 26 March 2006 |
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Junior Observer |  |
| News Business Features Editorial
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Keyboards and switches In a previous issue, we introduced you to computer keyboards. This week you can learn more about them. A computer can also use separate character maps, overriding the one found in the keyboard. This can be useful if a person is typing in a language that uses letters that don't have English equivalents on a keyboard with English letters. People can also set their computers to interpret their keystrokes as though they were typing on a Dvorak keyboard, even though their actual keys are arranged in a QWERTY layout. In addition, operating systems and applications have keyboard accessibility settings that let people change their keyboard's behaviour to adapt to disabilities.
Keyboards use a variety of switch technologies. 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 its bottom. 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 (was explained in the previous article)changes. 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.
All other types of switches used in keyboards are mechanical in nature. Each provides a different level of audible and tactile (touch-sensitive) response - the sounds and sensations that typing creates. Mechanical key switches include rubber dome, membrane, metal contact and foam element. Rubber dome switches are very common. They use small, flexible rubber domes, each with a hard carbon centre. When you press a key, a plunger on the bottom of the key pushes down against the dome, and the carbon centre presses against a hard, flat surface beneath the key matrix. As long as the key is held, the carbon centre completes the circuit. When the key is released, the rubber dome springs back to its original shape, forcing the key back up to its at-rest position. Rubber dome switch keyboards are inexpensive, have pretty good tactile responses and are fairly resistant to spills and corrosion because of the rubber layer covering the key matrix. Rather than having a switch for each key, membrane keyboards use a continuous membrane that stretches from one end to another. A pattern printed in the membrane completes the circuit when you press a key. Some membrane keyboards use a flat surface printed with representations of each key rather than keycaps. Membrane keyboards don't have good tactile response, and without additional mechanical components, they don't make the clicking sound that some people like to hear when they're typing. However, they're generally inexpensive to make. Metal contact and foam element keyboards are increasingly becoming common. Metal contact switches simply have a spring-loaded key with a strip of metal on the bottom. When the key is pressed, the metal strip connects the two parts of the circuit. The foam element switch is basically the same design, but with a small piece of spongy foam between the bottom of the plunger and the metal strip, providing a better tactile response. Both technologies have good tactile response, make satisfyingly audible 'clicks,' and are inexpensive to produce. The problem is that the contacts tend to wear out or corrode faster than on keyboards that use other technologies. Also, there is no barrier that prevents dust or liquids from coming in direct contact with the circuitry of the key matrix. Non-traditional keyboards Different manufacturers have used these standard technologies, and a few others, to create a wide range of non-traditional keyboards. A lot of modifications to the traditional keyboard design are an attempt to make them safer or easier to use. For example, some people have associated increased keyboard use with repetitive stress injuries, although scientific studies have produced conflicting results. Ergonomic(more suited to the environment or work) keyboard designs are intended to keep a person's hands in a more natural position while typing, in an attempt to prevent injuries. While these keyboards can certainly keep people from holding their hands in a 'praying mantis' position, studies disagree on whether they actually prevent injury. With the exception of the Virtual Laser Keyboard, which has its own sensing system, each of these keyboards use the same type of technology as traditional models do, to communicate with the computer. As you type, the processor in the keyboard analyses the key matrix and determines what characters to send to the computer. It maintains these characters in its memory buffer and then sends the data. 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. Wireless keyboards, on the other hand, connect to the computer through infrared (IR), radio frequency (RF) or Bluetooth connections. IR and RF connections are similar to what you'd find in a remote control. Regardless of which sort of signal they use, wireless keyboards require a receiver, either built in or plugged in to the USB port, to communicate with the computer. Since they don't have a physical connection to the computer, wireless keyboards have an AC power connection or use batteries for power. 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. 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. |
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