Keyboard technology
The technology of computer keyboards includes many elements. Many different keyboard technologies have been developed to meet consumer demands and optimized for industrial applications. The standard full-size computer alphanumeric keyboard typically uses 101 to 105 keys; keyboards integrated in laptop computers are typically less comprehensive.
Virtual keyboards, which are mostly accessed via a touchscreen interface, have no physical switches and provide artificial audio and haptic feedback instead. This variety of keyboard can prove useful, as it is not limited by the rigid nature of physical computer keyboards.
The majority of modern keyboards include a control processor and indicator lights to provide feedback to the user about what state the keyboard is in. Plug-and-play technology means that its "out of the box" layout can be notified to the system, making the keyboard immediately ready to use without the need for further configuration, unless the user so desires. This also enables manufacture of generic keyboards for a variety of language markets, that differ only in the symbols engraved on the keytops.
Keystroke sensing
Membrane
A common membrane design consists of three layers. The top and bottom layer have exposed electrical matrix traces, and the middle layer is a spacer to prevent current from passing through the top and bottom conductive traces passively. When pressure is applied to the top membrane, it bridges the top and bottom conductive contact pads, allowing current to transfer.Two of the most common types of membrane keyboards include full-travel rubber dome over membrane and flat-panel membrane keyboards. Flat-panel membrane keyboards are most often found on appliances like microwave ovens or photocopiers.
Rubber dome over membrane
Full-travel rubber dome over membrane keyboards are the most common keyboard design manufactured today. In these keyboards, a rubber dome sheet is placed above the membranes, ensuring that the domes align with the contact pads. The rubber dome serves a dual purpose: it acts as a tactile return spring and provides a soft surface to transfer force onto the top membrane. To bridge the connection between the two contact pads, the rubber dome must be fully depressed.Rubber dome over membrane keyboards became very popular with computer manufacturers as they sought to reduce costs while PC prices declined.
Scissor-switch
A common, compact variant of rubber dome over membrane is the scissor-switch, based on the scissors mechanism. Due to the requirement of many notebooks to be slim, they require the keyboards to be low-profile. Therefore, this technology is most commonly featured on notebooks. 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 keycap. 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 but also less likely to get debris in them as the gaps between the keys are often smaller.
Flat-panel membrane
Flat-panel membrane keyboards are often used in harsh environments where water or leak-proofing is desirable. They can have non-tactile, polydome tactile and metal dome tactile keys. Polydome tactile membrane switches use polyester, or PET, and is formed to create a stiff plastic dome. When the stiff polydome is pressed, the conductive ink on the back of the polydome connects with the bottom layer of the circuit. Metal dome membrane switches are made of stainless steel and offer enhanced durability and reliability and can feature custom dome designs. Non-tactile flat-panel membrane keyboards have little to no keypress feel and often issue a beep or flash of light on actuation.Although this keyboard design was commonly used in the early days of the personal computer, they have been supplanted by more responsive and modern designs.
Roll-up keyboard
Computer keyboards made of flexible silicone or polyurethane materials can roll up in a bundle. This type of keyboard can take advantage of the thin flexible plastic membranes, but still pose the risk of damage. When they are completely sealed in rubber, they are water resistant. Roll-up keyboards provide relatively little tactile feedback. Because these keyboards are typically made of silicone, they unfavorably tend to attract dirt, dust, and hair.Metal contact
Keyboards which have metal contact switches typically use discrete modules for each key. This type of switch are usually composed of a housing, a spring, and a slider, and sometimes other parts such as a separate tactile leaf or clickbar.file:Cherry MX -- switch contacts.jpg|thumb|right|Cherry MX switch contacts
At rest, the metal contacts inside of the switch are held apart. As the switch is pressed down, the contacts are held together to conduct current for actuation. Many switch designs use gold for contact material to prolong the lifetime of the switch by preventing switch failure from oxidization. Most designs use a metal leaf, where the movable contact is a leaf spring.
A major producer of discrete metal contact switches is Cherry, who has manufactured the Cherry MX family of switches since the 1980s. Cherry's color-coding system of categorizing switches has been imitated by other switch manufacturers, such as Gateron and Kailh among many others.
Keyboards which utilize this technology are commonly referred to as "mechanical keyboards", but there is not a universally agreed-upon clear-cut definition for this term.
Since mid-2000s, mechanical keyboards are used by gamers and professionals again.
Hot-swappable keyboard
keyboards are keyboards in which switches can be pulled out and replaced without requiring the typical solder connection. Instead of the switch pins being directly soldered to the keyboard's PCB, hot-swap sockets are instead soldered on. Hot-swap sockets can allow users to change different switches out of the keyboard without having the tools or knowledge required to solder.Reed
The reed module in a reed switch consists of two metal contacts inside of a glass bubble usually sealed with some inert gas like nitrogen to help prevent particle build-up. The slider in the housing pushes a magnet down in front of the reed capsule and the magnetic field causes the reed contacts to become attracted to each other and make contact. The reed switch mechanism was originally invented in 1936 by W B Ellwood at Bell Telephone Laboratories.Although reed switches use metal leaf contacts, they are considered separate from all other forms of metal contact switch because the contacts are operated magnetically instead of using physical force from a slider to be pressed together.
Capacitive
In a capacitive mechanism, 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 and covered by a thin, insulating film of soldermask which acts as a dielectric.For the most common, foam and foil implementation of this technology, 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 a 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.
An advantage of the capacitive technology is that the switch is not dependent on the flow of current through metal contacts to actuate. There is no debouncing necessary.
The sensor tells enough about the distance of the keypress to allow the user to adjust the actuation point. This adjustment can be done with the help of the bundled software and individually for each key, if so implemented. A keyboard which utilizes these abilities include the Real Force RGB.
IBM's Model F keyboard is a design consisting of a buckling spring over a capacitive PCB, similar to the later Model M keyboard, but instead used membrane sensing in place of a PCB.
The Topre Corporation design for switches uses a conical spring below a rubber dome. The dome provides resistance, while the spring does the capacitive action.
Hall effect
keyboards use Hall effect sensors to detect the movement of a magnet by the potential difference in voltage. 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.A hall switch works through magnetic fields. Every switch has a small magnet fixed inside it. When the electricity passes through the main circuit, it creates a magnetic flux. Every time a key is pressed, the magnetic intensity changes. This change is noticed by the circuit and the sensors send the information to the motherboard.
Optical
Optical switch technology was introduced in 1962 by Harley E. Kelchner for use in a typewriter machine with the purpose of reducing the noise generated by typewriter keys.An optical keyboard technology utilizes light-emitting devices and photo sensors to optically detect actuated keys, offering faster response times and eliminating the need for physical contact between moving parts. 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 two beams 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.
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.
A major advantage of optical switch technology is that it is very resistant to moisture, dust, and debris because there are no metal contacts that can corrode.
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.