Keyboard technology

There are many types of keyboards, usually differentiated by the switch technology employed in their operation. Since there are so many switches needed (usually about 80-110) and because they have to be highly reliable(SONY Vaio VGN-FW32J Battery), this usually defines the keyboard. The choice of switch technology affects key response (the positive feedback that a key has been pressed) and travel (the distance needed to push the key to enter a character reliably) (SONY Vaio VGN-FW17W Battery). Newer models use hybrids of various technologies to achieve greater cost savings.

Types

Membrane keyboard

Main article: Membrane keyboard

There are two types of membrane-based keyboards: Flat-panel membrane keyboards and full-travel membrane keyboards(SONY Vaio VGN-FW31E Battery):

Flat-panel membrane keyboards are most often found on appliances like microwave ovens or photocopiers. A common design consists of three layers. The top layer (and the one the user touches) has the labels printed on its front and conductive stripes printed on the back. Under this it has a spacer layer(SONY Vaio VGN-FW139E Battery), which holds the front and back layer apart so that they do not normally make electrical contact. The back layer has conductive stripes printed perpendicularly to those of the front layer. When placed together, the stripes form a grid(SONY Vaio VGN-FW139E/H Battery). When the user pushes down at a particular position, their finger pushes the front layer down through the spacer layer to close a circuit at one of the intersections of the grid. This indicates to the computer or keyboard control processor that a particular button has been pressed(SONY Vaio VGN-FW465J Battery).

Generally, flat-panel membrane keyboards do not have much of a "feel", so many machines which use them issue a beep or flash a light when the key is pressed. They are often used in harsh environments where water or leak proofing is desirable(SONY Vaio VGN-FW31M Battery). Although used in the early days of the personal computer (on the ZX80, ZX81 and Atari 400), they have been supplanted by the more tactile dome and mechanical switch keyboards. However, membrane keyboards with interchangeable key layouts, such as the IntelliKeys and Discover(SONY VAIO VGN-FZ21E Battery):board are still commonly used by people with physical, visual, or cognitive disabilities as well as people who require assistive technology to access a computer(SONY VAIO VGN-FZ21Z Battery).

Full-travel membrane-based keyboards are the most common computer keyboards today. They have one-piece plastic keytop/switch plungers which press down on a membrane to actuate a contact in an electrical switch matrix(SONY VAIO VGN-FZ21J Battery).

Dome-switch keyboard

How a dome-switch keyboard works: Finger depresses the dome to complete the circuit

Dome switches mesh with keys (keyboard is upside down in this image) (SONY Vaio VGN-FW11 Battery)

Dome switch keyboards are a hybrid of flat-panel membrane and mechanical keyboards. They bring two circuit board traces together under a rubber or silicone keypad using either metal "dome" switches or polyester formed domes(SONY Vaio VGN-FW11M Battery). The metal dome switches are formed pieces of stainless steel that, when compressed, give the user a crisp, positive tactile feedback. These metal types of dome switches are very common, are usually reliable to over 5 million cycles(SONY Vaio VGN-FW11S Battery), and can be plated in either nickel, silver or gold. The rubber dome switches, most commonly referred to as polydomes, are formed polyester domes where the inside bubble is coated in graphite. While polydomes are typically cheaper than metal domes, they lack the crisp snap of the metal domes(SONY Vaio VGN-FW21E Battery), and usually have a lower life specification. Polydomes are considered very quiet, but purists tend to find them "mushy" because the collapsing dome does not provide as much positive response as metal domes. For either metal or polydomes(SONY Vaio VGN-FW21J Battery), when a key is pressed, it collapses the dome, which connects the two circuit traces and completes the connection to enter the character. The pattern on the PC board is often gold-plated(SONY Vaio VGN-FW21L Battery).

Both are common switch technologies used in mass market keyboards today. This type of switch technology happens to be most commonly used in handheld controllers, mobile phones, automotive, consumer electronics and medical devices. Dome switch keyboards are also called direct-switch keyboards(SONY Vaio VGN-FW21M Battery).

See also: Chiclet keyboard

Scissor-switch keyboard

Main article: Scissor-switch technology (keyboard terminology)

A special case of the computer keyboard dome-switch is the scissor-switch. The keys are attached to the keyboard via two plastic pieces that interlock in a "scissor"-like fashion, and snap to the keyboard and the key. It still uses rubber domes(SONY VGP-BPS13Q Battery), but a special plastic 'scissors' mechanism links the keycap to a plunger that depresses the rubber dome with a much shorter travel than the typical rubber dome keyboard. Typically scissor-switch keyboards also employ 3-layer membranes as the electrical component of the switch(SONY VGP-BPS13B/Q Battery). These stabilizing scissor-like devices extend the lifespan of the membrane to as much as 10 million keystrokes.[citation needed] They also usually have a shorter total key travel distance (2 mm instead of 3.5 – 4 mm for standard dome-switch keyswitches) (SONY VGN NR11S/S battery). This type of keyswitch is often found on the built-in keyboards on laptops and keyboards marketed as 'low-profile'. These keyboards are generally quiet and the keys require little force to press(SONY VGN NR11M/S battery).

Scissor-switch keyboards are typically slightly more expensive. They are harder to clean (due to the limited movement of the keys and their multiple attachment points) but also less likely to get debris in them as the gaps between the keys are often less (as there is no need for extra room to allow for the 'wiggle' in the key as you would find on a membrane keyboard) (SONY VGN NR11Z/S battery).

Capacitive keyboard

In this type of keyboard, pressing the key changes the capacitance of a pattern of capacitor pads. Unlike "dome switch" keyboards, the pattern consists of two D-shaped capacitor pads for each switch, printed on a printed circuit board (PC board) and covered by a thin, insulating film of soldermask which plays the role of a dielectric(SONY VGN NR11Z/T battery). The mechanism of capacitive switches is very simple, compared to mechanical ones. Its movable part is ended with a flat foam element (of dimensions near to a tablet of Aspirin) finished with aluminium foil below. The opposite side of the switch is a PC board with the capacitor pads(SONY VGP-BPS13A/Q Battery).

When a key is pressed, the foil tightly clings to the surface of the PC board, forming a daisy chain of two capacitors between contact pads and itself separated with thin soldermask(SONY VGP-BPS21/S Battery), and thus "shorting" the contact pads with an easily detectable drop of capacitive reactance between them. Usually this permits a pulse or pulse train to be sensed. The keys do not need to be fully pressed to be fired on, which enables some typists to work faster(SONY VGP-BPS21 Battery).

As of 2008 they are a rare find in generic PC keyboards[citation needed]. Vintage PCs may in some cases be equipped with this type of keyboard, because the original IBM keyboards for the Personal Computer, Personal Computer XT(SONY VGP-BPS21B Battery), and Personal Computer AT were Model F keyboards, which used the buckling spring mechanism to actuate a capacitative switch, unlike the 101-key Enhanced Keyboard, also known as the Model M(SONY VGP-BPS21A/B Battery), which also had the buckling spring mechanism, but a membrane contact switch. At the present time, the best-known keyboard for use with desktop personal computers that uses a capacitative switch is that made by Topre, either under its own name(SONY VAIO PCG-5K1L battery), or for Fujitsu, which sells a keyboard custom-manufactured for it to its specifications as the Happy Hacking Keyboard. The Topre mechanism uses a spring underneath a rubber dome, and the depression of the spring causes a change in capacitance between the underlying capacitor pads(SONY VAIO PCG-6W2L battery).

There are also industrial makes of flat-panel capacitive keyboards that are inexpensive, and they resist wear, water, foreign objects and dirt.

Mechanical-switch keyboard

Mechanical-switch keyboards use real switches, one under each key. Depending on the construction of the switch, these keyboards have varying responses and travel times. Notable keyboards utilizing this technology are the Apple Extended Keyboard (the original and/or the "II")(SONY VAIO PCG-7112L battery), as well as its modern imitator, the Matias Tactile Pro. These two keyboards use ALPS switches. On PCs, the OmniKey series from Northgate Computers was popular and the line is now carried by Creative Vision Technologies under the Avant brand(SONY VAIO PCG-8Z1L battery). Cherry Corporation of Germany also makes mechanical switches used in special purpose and high end keyboards. Their popular MX series of keyswitches are available in three actuation force/travel designs(SONY VAIO PCG-8Z2L battery), often referred to by the colour of the centre stem to which the keycap attaches: black is a linear feel where the force increases monotonically as the key is pressed, brown provides tactile feedback as the force required decreases just before the key actuates(SONY VAIO PCG-8Y2L battery), and blue which is tactile and also has a click sound. In India, the TVS Gold mechanical keyboard is very popular despite costing about five times as much as a membrane keyboard(SONY VAIO PCG-8Y1L battery).

Buckling-spring keyboard

Many typists prefer buckling-spring keyboards. The buckling spring mechanism (expired U.S. Patent 4,118,611) atop the switch is responsible for the tactile and aural response of the keyboard. This mechanism controls a small hammer that strikes a capacitive or membrane switch(SONY VAIO PCG-7Z2L battery).

In 1993, two years after spawning Lexmark, IBM transferred its keyboard operations to the daughter company. New Model M keyboards continued to be manufactured for IBM by Lexmark until 1996, when Unicomp purchased the keyboard technology(SONY VAIO PCG-7Z1L battery).

Today, new buckling-spring keyboards are manufactured by Unicomp. Unicomp also repairs old IBM and Lexmark keyboards(SONY VAIO PCG-7133L battery).

Hall-effect keyboard

Hall effect keyboards use magnets and Hall effect sensors instead of an actual switch. When a key is depressed, it moves a magnet, which is detected by the solid-state sensor. These keyboards are extremely reliable(SONY VAIO PCG-7113L battery), and are able to accept millions of keystrokes before failing. They are used for ultra-high reliability applications, in locations like nuclear powerplants or aircraft cockpits. They are also sometimes used in industrial environments(SONY VAIO PCG-6W3L battery). These keyboards can be easily made totally waterproof. They also resist large amounts of dust and contaminants. Because a magnet and sensor is required for each key, as well as custom control electronics, they are very expensive(SONY VAIO PCG-7111L battery).

Laser keyboard

A laser projection device approximately the size of a computer mouse projects the outline of keyboard keys onto a flat surface, such as a table or desk. This type of keyboard is portable enough to be easily used with PDAs and cellphones(SONY VAIO PCG-6W1L battery), and many models have retractable cords and wireless capabilities. However, sudden or accidental disruption of the laser will register unwanted keystrokes. Also, if the laser malfunctions, the whole unit becomes useless, unlike conventional keyboards which can be used even if a variety of parts (such as the keycaps) are removed(SONY VAIO PCG-6V1L battery). This type of keyboard can be frustrating to use since it is susceptible to errors, even in the course of normal typing, and its complete lack of tactile feedback makes it even less user-friendly than the cheapest membrane keyboards(SONY VAIO PCG-6S3L battery).

Roll-up keyboard

Most keyboards are rigid, but this foldable keyboard demonstrates one of many variations from the usual(SONY VAIO PCG-6S2L battery).

Some keyboards are designed out of flexible materials that can roll up in a moderately tight bundle. Normally the external materials are either silicone or polyurethane. It is important to note that although many manufacturers claim that the keyboards are foldable(SONY VAIO PCG-5J2L battery), they cannot be folded without damaging the membrane that holds the circuitry. Typically they are completely sealed in rubber, making them watertight like membrane keyboards. Like membrane keyboards, they are reported to be very hard to get used to, as there is little tactile feedback(SONY VAIO PCG-5L1L battery).

As of 2005, roll-up keyboards include:

the CoolMac keyboard [1],

the Eumax keyboard,

the VIK ("virtually indestructible keyboard") [2], [3],

the pocket VIK [4],

the Flexboard keyboard [5],

the CoolMIR keyboard [6], and

the Whitelite FX100 Keyboard [7].

See Roll-away computer(SONY VAIO PCG-5K2L battery).

Optical keyboard technology

Also known as photo-optical keyboard, light responsive keyboard, photo-electric keyboard and optical key actuation detection technology(SONY VAIO PCG-5J1L battery).

The optical keyboard technology has been introduced in 1962 by Harley E. Kelchner – for use in a typewriter machine with the purpose of reducing the noise generating by actuating the typewriter keys(SONY VAIO PCG-5G3L battery).

An optical keyboard technology utilizes light-emitting devices and photo sensors to optically detect actuated keys. Most commonly the emitters and sensors are located in the perimeter, mounted on a small PCB(SONY VAIO PCG-5G2L battery). The light is directed from side to side of the keyboard interior and it can only be blocked by the actuated keys. Most optical keyboards require at least 2 beams (most commonly vertical beam and horizontal beam) to determine the actuated key(SONY VGP-BPS13B/S Battery). Some optical keyboards use a special key structure that blocks the light in a certain pattern, allowing only one beam per row of keys (most commonly horizontal beam) (SONY VGP-BPS13S Battery).

The mechanism of the optical keyboard is very simple – a light beam is sent from the emitter to the receiving sensor, the actuated key blocks, reflects, refracts or otherwise interacts with the beam, resulting in an identified key(SONY VGP-BPS13AS Battery).

Some earlier optical keyboards were limited in their structure and required special casing to block external light, no multi-key functionality was supported and the design was very limited to a thick rectangular case(SONY VGP-BPS13A/S Battery). None of the known optical technologies were ever developed to a mass production stage, with the exception of MOBBAL Keyboard Technology by Aymer International. MOBBAL Technology allows almost any shape and design of the keyboard, and can be used for laptop and desktop keyboards, ATM keypads etc(Sony VAIO VGN-FZ15G Battery).

The advantage of the optical keyboard technology is that it offers a real waterproof keyboard, resilient to dust and liquids, it is electromagnetic emissions free (thus cannot be eavesdropped to wirelessly) and it uses about 20% PCB volume(Sony VAIO VGN-FZ15T Battery), compare with the membrane keyboard or dome switch keyboards, significantly reducing the electronic waste. The advantage of the optical keyboard technology over other keyboards such as Hall effect keyboard(SONY VGP-BPS13/B Battery), laser keyboard, roll-up keyboard and transparent keyboard lies in cost (Hall effect keyboard) and feel – the optical keyboard technology do not require different key mechanism, typing tactile feeling remains to offer its user the same known feeling of the keyboard, for over 60 years(SONY VGP-BPS13B/B Battery).

The specialist Datahand keyboard uses optical technology to sense keypresses, with a single light beam and sensor per key. The keys are held in their rest position by magnets; when the magnetic force is overcome to press a key, the optical path is unblocked and the keypress is registered(SONY VGP-BPS13 Battery).

Debouncing

When pressing a keyboard key, the key "bounces" like a ball against its contacts several times before it settles into firm contact. When released, it bounces some more until it reverts to the uncontacted state. If the computer was watching for each pulse, it would see many keystrokes for what the user thought was just one(SONY VAIO VGN-FZ31B Battery).

To resolve this problem, the processor in a keyboard (or computer) "debounces" the keystrokes, by aggregating them across time to produce one "confirmed" keystroke that (usually) corresponds to what is typically a solid contact(SONY VAIO VGN-FZ31M Battery). It could be argued that the dome switch technology outlined above owes its popularity to the ability of the processor to accurately debounce the keystrokes. Early membrane keyboards limited typing speed because they had to do significant debouncing. This was a noticeable problem on the ZX81(SONY VAIO VGN-FZ31J Battery).

Keytops

Keytops are used on full-travel keyboards. While modern keycaps are typically surface-printed, they can also be 2-shot molded, laser printed, sublimation printed, engraved, or they can be made of transparent material with printed paper inserts(SONY VAIO VGN-FZ31E Battery).

There are also Keycaps, which are thin shells that are placed over keytop bases. These were especially used on IBM PC keyboards(Sony Vaio VGN-FZ31S battery).

Other parts of the PC keyboard

The modern PC keyboard also includes a control processor and indicator lights to provide feedback to the user about what state the keyboard is in. Depending on the sophistication of the controller's programming, the keyboard may also offer other special features(SONY VAIO VGN-FZ31z Battery). The processor is usually a single chip 8048 microcontroller variant. The keyboard switch matrix is wired to its inputs and it processes the incoming keystrokes and sends the results down a serial cable (the keyboard cord) to a receiver in the main computer box. It also controls the illumination of the "caps lock", "num lock" and "scroll lock" lights(SONY VAIO VGN-FZ38M Battery).

A common test for whether the computer has crashed is pressing the "caps lock" key. The keyboard sends the key code to the keyboard driver running in the main computer; if the main computer is operating, it commands the light to turn on. All the other indicator lights work in a similar way(SONY VAIO VGN-FZ210CE Battery). The keyboard driver also tracks the shift, alt and control state of the keyboard.