Editing Keyboard technology (section)

== Keystroke sensing ==

=== Membrane ===
{{Main|Membrane keyboard}}
[[File:AppleDesign Keyboard (NMB,B) -- membrane assembly 4.jpg|thumb|right|A typical membrane assembly]]
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 oven]]s or [[photocopier]]s.

==== {{anchor|Dome-switch keyboard}} Rubber dome over membrane ====
[[File:Rubber dome over membrane, exploded.svg|thumb|center|Exploded view of a typical rubber dome over membrane design]]
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 =====
{{See also|Chiclet keyboard}}
[[File:Scissor switch mechanism.svg|thumb|Scissor switch mechanism]]
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 (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).<ref>{{Citation |title=Keyboards |access-date=21 April 2009 |archive-url=https://web.archive.org/web/20120222204455/http://www.ergocanada.ca/ergo/keyboards/mechanical_vs_membrane_keyswitches.html |url-status=live |contribution=Mechanical vs membrane keyswitches |contribution-url=http://www.ergocanada.ca/ergo/keyboards/mechanical_vs_membrane_keyswitches.html |place=[[Canada|CA]] |publisher=Ergo |archive-date=22 February 2012}}.</ref>{{clear}}

==== Flat-panel membrane ====
[[File:Atari 400 keyboard.jpg|thumb|Atari 400 keyboard]]
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.<ref>{{cite web | url=http://www.dotkeys.in/membrane-keyboards.html | title=Dotkeys &#124; Membrane Switches }}</ref> 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]] (on the [[Sinclair ZX80]], [[ZX81]], and [[Atari 400]]), they have been supplanted by more responsive and modern designs.

==== Roll-up keyboard ====
[[File:Foldable keyboard.jpg|thumb|Most keyboards are rigid, but this keyboard is flexible.]]
{{See also|Roll-away computer}}
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.<ref>{{cite web | url=https://keyboardsexpert.com/roll-up-keyboards/ | title=Roll-Up Keyboards - What are They and Are They Durable? | date=12 November 2021 }}</ref>{{clear}}

=== Metal contact ===
[[File:Cherry MX -- opened, 2.jpg|thumb|right|Cherry MX Blue (left) and disassembled Cherry MX Brown (right)]]
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 (company)|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.<ref>{{cite web |last1=Smith |first1=Ernie |title=The Company That Makes Mechanical Keyboards Clack |url=https://www.vice.com/en/article/the-company-that-makes-mechanical-keyboards-clack/ |website=Vice |access-date=11 September 2021 |date=10 July 2018 |archive-date=11 September 2021 |archive-url=https://web.archive.org/web/20210911200340/https://www.vice.com/en/article/a3qzy5/the-company-that-makes-mechanical-keyboards-clack |url-status=live }}</ref><ref>{{cite web |last1=Burek |first1=John |last2=Brant |first2=Tom |last3=Wilson |first3=Jeffrey L. |title=The Best Keyboards for 2021 |url=https://www.pcmag.com/picks/the-best-keyboards |website=PC Mag |access-date=11 September 2021 |date=19 July 2021 |archive-date=11 September 2021 |archive-url=https://web.archive.org/web/20210911081252/https://www.pcmag.com/picks/the-best-keyboards |url-status=live }}</ref>

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.<ref>{{Cite web |last=Shark |first=Admiral |date=30 May 2021 |title=The problems with the term 'mechanical keyboard' |url=https://sharktastica.co.uk/gists/mech_term_bad |access-date=2023-12-08 |website=Admiral Shark's Keyboards |language=English}}</ref>

==== Hot-swappable keyboard ====
[[Hot swapping|Hot-swappable]] keyboards are keyboards in which switches can be pulled out and replaced without requiring the typical [[soldering|solder]] connection.<ref>{{cite web |last1=Schoon |first1=Eric |title=The 8 Best Hop Swappable Mechanical Keyboards |url=https://www.reviewgeek.com/34512/the-4-best-hot-swappable-mechanical-keyboards/ |website=Review Geek |access-date=11 September 2021 |date=28 June 2021 |archive-date=11 September 2021 |archive-url=https://web.archive.org/web/20210911193554/https://www.reviewgeek.com/34512/the-4-best-hot-swappable-mechanical-keyboards/ |url-status=live }}</ref><ref>{{cite web |last1=Porter |first1=Jon |title=The Keychron Q1 Is an Enthusiast-Quality Keyboard Right Out of the Box |url=https://www.theverge.com/22662686/keychron-q1-review-price-mechanical-keyboard-features |website=The Verge |access-date=11 September 2021 |date=9 September 2021 |archive-date=11 September 2021 |archive-url=https://web.archive.org/web/20210911081024/https://www.theverge.com/22662686/keychron-q1-review-price-mechanical-keyboard-features |url-status=live }}</ref> Instead of the ''switch'' pins being directly soldered to the keyboard's [[printed circuit board|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 ===
[[File:Omron B2R-M -- reed module removed.jpg|thumb|Reed switch with reed module removed]]
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 ===
[[File:Topre switch.png|right|thumb|Topre electrostatic capacitive switch]]
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]] (PCB) 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 [[Tablet (pharmacy)|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 [[series circuits|daisy chain]] of two capacitors between [[contact pad]]s and itself separated with a thin soldermask, and thus "shorting" the [[contact pad]]s 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 (key sensitivity). This adjustment can be done with the help of the bundled software and individually for each key, if so implemented.<ref>Topre keyboard documentation, describing various features [http://www.realforce.co.jp/en/products/R2SA-US4-IV/index.html] {{Webarchive|url=https://web.archive.org/web/20190723000131/http://www.realforce.co.jp/en/products/R2SA-US4-IV/index.html|date=23 July 2019}} and they software manual [http://www.realforce.co.jp/en/support/download/REALFORCE_Software_Manual_EN.pdf pdf] {{Webarchive|url=https://web.archive.org/web/20210917195133/https://www.realforce.co.jp/en/support/download/REALFORCE_Software_Manual_EN.pdf|date=17 September 2021}}</ref> 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|Topre Corporation]] design for switches uses a conical spring below a rubber dome. The dome provides resistance, while the spring does the capacitive action.<ref>{{Cite magazine |last1=Wong |first1=Anson |last2=Li |first2=Tom |date=6 April 2019 |title=The complete guide to mechanical keyboard switches for gaming |url=https://www.pcgamer.com/best-mechanical-switches-for-gaming/ |magazine=[[PC Gamer]] |access-date=9 January 2020 |archive-date=4 March 2020 |archive-url=https://web.archive.org/web/20200304195543/https://www.pcgamer.com/best-mechanical-switches-for-gaming/ |url-status=live }}</ref>{{clear}}

=== Hall effect ===
[[file:RAFI RS 76 C 010 -- fully disassembled, top views.jpg|thumb|RAFI RS 76 C 010 hall effect switch fully disassembled]]
[[Hall effect]] keyboards use [[Hall effect sensor]]s 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_effect_sensor#Human interface devices|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.<ref>{{Cite web |last=James |first=Elliana |date=21 November 2020 |title=Keyboards with Hall Effect Technology – Why is it better than other switches? |url=https://keybolab.com/hall-effect-keyboard-switches/ |website=Keybolab}}</ref>

=== 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 diode|light-emitting devices]] and [[Photoelectric sensor|photo sensors]] to optically detect actuated keys. Most commonly the emitters and sensors are located at the perimeter, mounted on a small [[Printed circuit board|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 (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, [[Reflection (physics)|reflects]], [[Refraction|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 [[magnet]]s; when the magnetic force is overcome to press a key, the optical path is unblocked and the keypress is registered.

=== Laser projection ===
{{Main|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 [[Personal digital assistant|PDA]]s and cellphones, and many models have retractable cords and wireless capabilities. However, this design is prone to error, as accidental disruption of the laser will generate unwanted keystrokes. This type of keyboard's inherent lack of tactile feedback makes it often undesirable.