Editing Keystroke sensing (section)

==Electromagnetic==
While all full-travel keyboards require moving parts to function, conductive switches have extra moving parts that wear out with use. Switch lifetime can be increased by replacing the physical switch contacts with electromagnetism. In addition to greatly improved longevity, electromagnetic sensing also significantly reduces the friction in the switch feel compared to metal leaf switches, as the slider is not rubbing against movable switch contacts.

===Capacitive===
{{Main|Capacitive keyboard}}

A capacitive contact mechanism makes use of a property of capacitors, that their capacitance is related to the distance between the plates that make up the capacitor. A capacitive keyboard switch moves a conductive object towards a pair of pads on the PCB, which are connected to a signal generator. Capacitive contacts have a long expected lifetime, but are also quite expensive and have thus fallen out of popularity for general purpose usage. Capacitive keyboards also have the advantage of not suffering from [[ghosting]] due as they are not dependent on the flow of current through the contacts. They are however sensitive to contamination affecting the capacitive sensing, but usually this can be resolved by cleaning the switch. Capacitive sensing lives on as the basis of most [[touch screen]] and [[trackpad]] technology used today.

[[IBM]] made use of capacitive sensing in [[beam spring]] and capacitive [[buckling spring]] keyboards, both very highly regarded designs. The most common implementation is [[foam and foil]], where the movable part of the variable capacitor is a foil disc placed onto the bottom of a foam pad (added to provide [[overtravel]]). [[BTC foam and foil]] and [[Key Tronic foam and foil]] are the most commonly occurring foam and foil implementations.

[[Topre Corporation|Topre]], with their very long-standing [[rubber dome]]-based [[Topre switch]], was left as the only known manufacturer of mainstream capacitive keyboards by the 2000s, but more recently, their switch design has been copied, with the [[Noppoo capacitive]] switch being the first to be recognised.

<gallery widths=250 heights=187>
File:KT foam and foil switch internals.jpg                   | [[Key Tronic foam and foil]] modules
File:BTC 5100 -- sliders with foil.jpg                       | [[BTC 5100]] foil discs (top of keyboard upside down)
File:BTC 5100 -- PCB (top).jpg                               | BTC 5100 PCB with pairs of sense pads
File:Noppoo Capacitive -- PCB, Dome Sheet, Spring.jpg        | [[Noppoo capacitive]]: variable capacitor formed from a conical spring over dual PCB pads, under a rubber dome sheet
</gallery>

See: [[:Category:Capacitive switches|List of capacitive switches]]

===Hall effect===
{{Main|Hall effect keyboard}}

Hall effect keyboards use a solid state sensor (in a microchip found inside each switch) to detect the movement of a magnet by the potential difference (voltage) that the magnet creates across a wire. A typical implementation of a Hall effect switch consists of a linear switch which has a magnet attached to the slider, whose movement when the key is pressed actuates the switch. They are extraordinarily reliable, with an expected lifetime measured in billions of key presses. However, they are too expensive for general use, and are usually reserved for military and aerospace applications.

Hall effect keyboards use discrete switches just as with most metal contact keyboards, but the switch modules typically have four legs instead of the two or three in metal contact switches. Four-leg switches are good indication of either Hall effect or magnetic valve.

[[Honeywell]] is by far the best known manufacturer of Hall effect keyboard switches and switches through their Micro Switch division. Similar switches were also made in Eastern Europe during the Soviet era, often copies of Honeywell's switches. [[RAFI]] in Germany still manufacture their long-standing [[RAFI RS 76 C|RS 76 C]] series of Hall effect keyboard switches.

<gallery widths=250 heights=187>
File:Micro Switch 15SD15-1-E top view.JPG     | [[Micro Switch SD Series]] switches
File:RAFI-RS76C-disassembled.jpg              | RAFI RS 76 C switch disassembled, showing the Hall sensor IC; the magnet is inside the slider
</gallery>

See: [[:Category:Hall effect switches|List of Hall effect switches]]

===Magnetic valve===
{{Main|Magnetic valve keyboard}}

Magnetic valve keyboards operate by controlling the flow of electrons using wire loops and a ferrite core. As current flows around one loop, it converts into a magnetic field generated inside the ferrite core. The movement of the magnetic field causes a flow of electrons in the second loop. To stop the flow of electrons, the magnetic field around the ferrite is stopped. This can be done by using a permanent magnet that has a magnetic orientation in another direction. Or by moving the ferrite far enough away from one of the loops that it can no longer generate sufficient current to be detected by the keyboard controller.<ref name="HaaTaGuide"/>

Magnetic valve keyboards can be fully or partially discrete, and in such cases, as with most Hall effect switches they have four legs. Where the wire loops are part of the PCB (as with ADI keyboards) this is itself a distinguishing characteristic.

[[ITW]], [[ADI]] and [[Nixdorf]] have used magnetic valve switches.

See: [[:Category:Magnetic valve switches|List of magnetic valve switches]]

===Inductive===
{{Main|Inductive keyboard}}

Inductive keyboard switches are built using an induction loop. The induction loop generates a magnetic field. To complete the circuit, and register a keypress, a metallic object is placed inside the loop. The presence of the metallic object will increase the overall current flowing through the wire which can be detected by the controller.

Inductive switches are common but the only known keyboard switch example was built by [[HP]] for one of their function generators in the 1970s.

See: [[:Category:Inductive switches|List of inductive switches]]