Editing Keystroke sensing (section)

===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]]