Keyboard technology

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Keyboard construction, in four layers, of a typical notebook computer keyboard Keyboard Construction.JPG
Keyboard construction, in four layers, of a typical notebook computer keyboard

Computer keyboards can be classified by the switch technology that they use. Computer alphanumeric keyboards typically have 80 to 110 durable switches, generally one for each key. The choice of switch technology affects key response (the positive feedback that a key has been pressed) and pre travel (the distance needed to push the key to enter a character reliably). Newer keyboard models use hybrids of various technologies to achieve greater cost savings.



Membrane keyboard

There are two types of membrane-based keyboards, flat-panel membrane keyboards and full-travel membrane keyboards:

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 has the labels printed on its front and conductive stripes printed on the back. Under this it has a spacer layer, 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. 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.

Generally, flat-panel membrane keyboards do not produce a noticeable physical feedback. Therefore, devices using these 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. Although used in the early days of the personal computer (on the Sinclair ZX80, ZX81 and Atari 400), they have been supplanted by the more tactile dome and mechanical switch keyboards.

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.

Dome-switch keyboard

How a dome-switch keyboard works: Finger depresses the dome to complete the circuit Keyboard Construction Button Press.JPG
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) Membrane keyboard.jpg
Dome switches mesh with keys (keyboard is upside down in this image)

Dome-switch keyboards are a hybrid of flat-panel membrane and mechanical-switch keyboards. They bring two circuit board traces together under a rubber or silicone keypad using either metal "dome" switches or polyurethane formed domes. 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, and can be plated in either nickel, silver or gold. The rubber dome switches, most commonly referred to as polydomes, are formed polyurethane 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, 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, 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.

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.

Scissor-switch keyboard

Scissor switch mechanism Scissor switch mechanism.svg
Scissor switch mechanism

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, 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. They also usually have a shorter total key travel distance (2 mm instead of 3.5 – 4 mm for standard dome-switch keyswitches). 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.

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 smaller (as there is no need for extra room to allow for the 'wiggle' in the key, as typically found on a membrane keyboard). [1]

Capacitive keyboard

In this type of keyboard, pressing a key changes the capacitance of a pattern of capacitor pads. The pattern consists of two D-shaped capacitor pads for each switch, printed on a printed circuit board (PCB) and covered by a thin, insulating film of soldermask which acts as a dielectric.

Despite the sophistication of the concept, the mechanism of capacitive switching is physically simple. The movable part ends with a flat foam element about the size of an aspirin tablet, finished with aluminum foil. Opposite the switch is a PCB with the capacitor pads. When the key is pressed, the foil tightly clings to the surface of the PCB, forming a daisy chain of two capacitors between contact pads and itself separated with thin soldermask, 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. Because the switch doesn't have an actual electrical contact, there is no debouncing necessary. The keys do not need to be fully pressed to be actuated, which enables some people to type faster. The sensor tells enough about the position of the key to allow the user to adjust actuation point (key sensitivity). This adjustment can be done with the help of the bundled software and individually for each key, if so implemented. [2]

The IBM Model F keyboard is mechanical-key design consisted of a buckling spring over a capacitive PCB, similarly to the later Model M keyboard that used a membrane in place of the PCB.

The most known company for their capacitive (electrostatic) switching technology is Topre Corporation [3] from Japan. However, while their products are for sale on eBay and Amazon (new and used), they are generally less available in large parts of the world. Topre's key switches use a spring below a rubber dome. The dome provides most of the force that keeps the key from being pressed, similar to a membrane keyboard, while the spring helps with the capacitive action. [4]

Mechanical-switch keyboard

Each key on a mechanical-switch keyboard contains a complete switch underneath. Each switch is composed of a housing, a spring, and a stem, and sometimes other parts such as a separate tactile leaf or a clickbar. Switches come in three variants: linear with consistent resistance; tactile with a non-audible bump; and clicky, a tactile with an audible click. [5] Depending on the resistance of the spring, the key requires different amounts of pressure to actuate and to bottom out. The shape of the stem as well as the design of the switch housing varies the actuation distance and travel distance of the switch. The amount of sound produced by actuation can also be changed by the addition of rubber dampeners. Like other types of keyboards, mechanical keyboards allow for the removal and replacement of keycaps, but replacing them is more common with mechanical keyboards due to common stem shapes.

Mechanical keyboards typically have a longer lifespan than membrane or dome-switch keyboards. Cherry MX switches, for example, have an expected lifespan of 50 million clicks per switch [6] , while switches from Razer have a rated lifetime of 60 million clicks per switch. [7]

The major current mechanical switch producer is Cherry. Alps Electric, a former major producer, ended production in the early 2000s, [8] but Alps style switches continue to be made by others companies as Matias, Xiang Min(XM), [9] Tai-Hao (APC) [10] and Hua-Jie (AK). [11] Other switch manufacturers include Gateron, [12] Kaihua (Kailh), [13] Gaote (Outemu), [14] Greetech, [15] TTC [16] and Omron.

Buckling-spring keyboard

Illustration from the original buckling spring U.S. Patent 4,118,611, issued to IBM in 1978. Bucklingspring1-o.svg
Illustration from the original buckling spring U.S. Patent 4,118,611 , issued to IBM in 1978.

Many typists prefer buckling spring keyboards. [17] 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. [18]

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 1999, when Unicomp purchased the keyboard technology.

Today, new buckling-spring keyboards are manufactured by Unicomp. Unicomp also repairs old IBM and Lexmark keyboards.

Hall-effect keyboard

Hall effect keyboards use magnets and Hall effect sensors instead of switches with mechanical contacts. When a key is depressed, it moves a magnet that is detected by a solid-state sensor. Because they require no physical contact for actuation, Hall-effect keyboards are extremely reliable and can accept millions of keystrokes before failing. They are used for ultra-high reliability applications such as nuclear power plants, aircraft cockpits, and critical industrial environments. They can easily be made totally waterproof, and can resist large amounts of dust and contaminants. Because a magnet and sensor are required for each key, as well as custom control electronics, they are expensive to manufacture.

Laser projection 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, 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. 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 lowest quality membrane keyboards.

Roll-up keyboard

Most keyboards are rigid, but this keyboard demonstrates one of many variations from the norm. Foldable keyboard.jpg
Most keyboards are rigid, but this keyboard demonstrates one of many variations from the norm.

Keyboards made of flexible silicone or polyurethane materials can roll up in a moderately tight bundle. Tightly folding the keyboard may damage the internal membrane circuits. When they are completely sealed in rubber they are water resistant. Like membrane keyboards, they are reported to be very hard to get used to, as there is little tactile feedback, and silicone will tend to attract dirt, dust, and hair.

Optical keyboard technology

Also known as photo-optical keyboard, light responsive keyboard, photo-electric keyboard, and optical key actuation detection technology.

Optical keyboard technology was 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.

An optical keyboard technology utilizes light-emitting devices and photo sensors to optically detect actuated keys. Most commonly the emitters and sensors are located at the perimeter, mounted on a small PCB. 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 a vertical beam and a horizontal beam) to determine the actuated key. 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 a horizontal beam).

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

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.

The advantages of optical keyboard technology are that it offers a real waterproof keyboard, resilient to dust and liquids; and it uses about 20% PCB volume, compared with membrane or dome switch keyboards, significantly reducing electronic waste. Additional advantages of optical keyboard technology over other keyboard technologies such as Hall effect, laser, roll-up, and transparent keyboards lie in cost (Hall effect keyboard) and feel – optical keyboard technology does not require different key mechanisms, and the tactile feel of typing has remained the same for over 60 years.

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.


When striking a keyboard key, the key oscillates (or bounces) against its contacts several times before settling. When released, it oscillates again until it reverts to its rest state. Although it happens on such a small scale as to be invisible to the naked eye, it's sufficient for the computer to register multiple key strokes inadvertently.

To resolve this problem, the processor in a keyboard "debounces" the keystrokes, by aggregating them across time to produce one "confirmed" keystroke that (usually) corresponds to what is typically a solid contact. Early membrane keyboards had limited typing speed because they had to do significant debouncing. This was a noticeable problem on the ZX81.[ citation needed ]


Keycaps are used on full-travel keyboards. While modern keycaps are typically surface-printed, they can also be double-shot molded, laser printed, sublimation printed, engraved, or they can be made of transparent material with printed paper inserts.

There are also keycaps which are thin shells that are placed over key bases. These were used on IBM PC keyboards.

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. 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.

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. The keyboard driver also tracks the shift, alt and control state of the keyboard.

Keyboard switch matrix

The keyboard switch matrix is often drawn with horizontal wires and vertical wires in a grid which is called a matrix circuit. It has a switch at some or all intersections, much like a multiplexed display. Almost all keyboards have only the switch at each intersection, which causes "ghost keys" and "key jamming" when multiple keys are pressed (rollover). Certain, often more expensive, keyboards have a diode between each intersection, allowing the keyboard microcontroller to accurately sense any number of simultaneous keys being pressed, without generating erroneous ghost keys. [19]

See also

Related Research Articles

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Microelectromechanical systems (MEMS), also written as micro-electro-mechanical systems and the related micromechatronics and microsystems constitute the technology of microscopic devices, particularly those with moving parts. They merge at the nanoscale into nanoelectromechanical systems (NEMS) and nanotechnology. MEMS are also referred to as micromachines in Japan and microsystem technology (MST) in Europe.

Chiclet keyboard Type of keyboard

Chiclet keyboard, island-style keyboard or flat keyboard is a type of input device for electronic systems such as personal computers, calculators and remote controls that uses keys in the shape of small squares with rounded corners and straight sides, in the style of Chiclets, an American chewing gum brand. A perforated bezel fills the gaps between the keys.

Membrane keyboard type of computer keyboard

A membrane keyboard is a computer keyboard whose "keys" are not separate, moving parts, as with the majority of other keyboards, but rather are pressure pads that have only outlines and symbols printed on a flat, flexible surface. Very little, if any, tactile feedback is felt when using such a keyboard, and error-free blind typing is difficult.

The Model F was a series of computer keyboards produced from 1981–1994 by IBM and later Lexmark. Its mechanical-key design consisted of a buckling spring over a capacitive PCB, similarly to the later Model M keyboard that used a membrane in place of the PCB.

Touchscreen input/output device usually layered on the top of an electronic visual display

A touchscreen, or touch screen, is a both input and output device and normally layered on the top of an electronic visual display of an information processing system. A user can give input or control the information processing system through simple or multi-touch gestures by touching the screen with a special stylus or one or more fingers. Some touchscreens use ordinary or specially coated gloves to work while others may only work using a special stylus or pen. The user can use the touchscreen to react to what is displayed and, if the software allows, to control how it is displayed; for example, zooming to increase the text size.

Buckling spring Mechanical switch mechanism famously used in IBM PC model M keyboard.

A buckling spring is a type of keyswitch mechanism, popularized by IBM's keyboards for the PC, PC/AT, 5250/3270 terminals, PS/2, and other systems. It was used by IBM's Model F keyboards, and the more common Model M. It is described in U.S. Patent 4,118,611 and U.S. Patent 4,528,431, both now expired.


A keypunch is a device for precisely punching holes into stiff paper cards at specific locations as determined by keys struck by a human operator. Other devices included here for that same function include the gang punch, the pantograph punch, and the stamp.

Key Tronic is a technology company founded in 1969. Its core products initially included keyboards, mice and other input devices. KeyTronic currently specializes in PCBA and full product assembly.

Kinesis (keyboard)

The Kinesis line of ergonomic computer keyboards is an alternative to the traditional keyboard design. Most widely known among these are the contoured Advantage line, which feature recessed keys in two bucket-like hollows which allow the fingers to reach keys with less effort as well as a central array of modifiers such as enter, alt, backspace, control, etc. where they can be pressed with the thumbs. All Kinesis keyboards support the capability to re-map individual keys. Recent models also come with the ability to switch between the Dvorak layout with the press of a special key combination, though keycaps printed with dual-legend QWERTY/Dvorak letters are included only on specific models. Moreover, the keys are laid out in perfect vertical rows to avoid the need for lateral movements during typing.

Membrane switch

A membrane switch is an electrical switch for turning a circuit on and off. It differs from a mechanical switch, which is usually made of copper and plastic parts: a membrane switch is a circuit printed on PET or ITO. The ink used for screen printing is usually copper / silver / graphite filled and therefore conductive.

Cherry (keyboards) company

Cherry GmbH is a German computer peripheral-device maker. The company has its roots in the United States and is headquartered in Germany. It has additional offices in the United States, France, and China. They manufactured a large range of products including sensors, vibrators and automotive modules until 1976, when Peter Cherry, the son of Walter L. Cherry, sold his company to ZF Friedrichshafen AG. Cherry was bought by ZF Freihadelibergur AG and renamed to ZF Electronics GmbH, the CHERRY naming was continued only for its computer input devices. Since the beginning of 2016 this product line has been operating independently on the market as the Cherry Group. After an eight-year partnership with ZF Friedrichshafen AG, Cherry was sold to GENUI Partners in October 2016.

Das Keyboard

Das Keyboard is a series of computer keyboards sold by Metadot Corporation, a software company located in Austin, Texas. Some models feature blank keycaps, supposedly to help improve touch typing skills and eliminate the need to rearrange keys for alternative keyboard layouts. Labeled versions have also been available since 2008. The current iterations employ mechanical keyswitches manufactured by either Cherry or Greetech.

Gateway AnyKey

The Gateway AnyKey is a programmable PC keyboard that was sold with desktop computers from the Gateway 2000 company roughly from 1990 to 1997. It was manufactured in at least five known versions and incarnations by Tucson, Arizona-based Maxi Switch, now a subsidiary of LiteOn Technology Corporation. The AnyKey is no longer manufactured, with the latest dated model available marked 1997. Maxi Switch, Gateway, and LiteOn currently do not offer any product labeled as or comparable to the AnyKey.

Projection keyboard

A projection keyboard is a form of computer input device whereby the image of a virtual keyboard is projected onto a surface: when a user touches the surface covered by an image of a key, the device records the corresponding keystroke. Some connect to Bluetooth devices, including many of the latest smartphone, tablet, and mini-PC devices with Android, iOS or Windows operating system.

A touch switch is a type of switch that only has to be touched by an object to operate. It is used in many lamps and wall switches that have a metal exterior as well as on public computer terminals. A touchscreen includes an array of touch switches on a display. A touch switch is the simplest kind of tactile sensor.


A keycap is a small plastic cover placed over the keyswitch of a computer keyboard. Keycaps are often illustrated to indicate the key function or alphanumeric character they correspond to. Early keyboards were manufactured with the keyswitch and keycap integrated in one unit; separate keycaps were introduced to facilitate the production of different keyboard layouts.

Silicone rubber keypads are used extensively in both consumer and industrial electronic products as a low cost and reliable switching solution.

Computer keyboard device comprising an arrangement of buttons or keys used to input text in computers

A computer keyboard is a typewriter-style device which uses an arrangement of buttons or keys to act as mechanical levers or electronic switches. Following the decline of punch cards and paper tape, interaction via teleprinter-style keyboards became the main input method for computers.

Tactile sensor device that measures information arising from physical interaction with its environment

A tactile sensor is a device that measures information arising from physical interaction with its environment. Tactile sensors are generally modeled after the biological sense of cutaneous touch which is capable of detecting stimuli resulting from mechanical stimulation, temperature, and pain. Tactile sensors are used in robotics, computer hardware and security systems. A common application of tactile sensors is in touchscreen devices on mobile phones and computing.


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