Editing Keystroke sensing (section)

===Reed===
A reed switch consists of two metal contacts, hermetically sealed and usually with some inert gas inside a glass envelope. The slider pushes a magnet down in front of the reed capsule. In a normally open switch, the magnetic field causes the reed contacts to become attracted to each other and to make contact; the contacts are themselves not magnetised. The reed switch mechanism was invented in 1936 by W B Ellwood at Bell Telephone Laboratories.

Reed switches support both normally open and normally closed operation. Hysteresis is also a standard feature; the degree of hysteresis present depends on the specification. Latching reed switches require alternating magnetic polarity to cycle the switch.<ref>RRE — [https://www.reed-sensor.com/general-reed-switch-faq/ Reed Switch and Reed Sensor FAQ!]</ref>

The reed capsule can be orientated in a number of ways. Fujitsu and Omron B2R series switches have the reed capsule orientated vertically, which demands a tall switch to contain it. To save space, Clare/Pendar low-profile switches have the reed capsule arranged diagonally in the vertical plane, while FR Electronics, IZOT and Unitra Dolam opted to place it horizontally across the bottom of the switch. Fujitsu also used the horizontal arrangement.

Although reed switches are metal leaf contact switches, here they are considered separate from all other forms of metal contact switch, even those with sealed contact assemblies such as [[Futaba complicated linear]], because the contacts are operated magnetically instead of using physical force.

<gallery widths=250 heights=187>
File:ASM MEXICO reed -- opened.jpg           | [[Clare-Pendar Series S880]], opened
File:ASM MEXICO reed -- internals, rear.jpg  | Internals, rear view; here, the magnet attaches directly to the return spring
File:ASM MEXICO reed -- reed capsule.jpg     | Reed capsule connected to the terminals via leads
</gallery>

[[Fujitsu Magnetic Reed]] and [[Omron B2R series]] are fairly different in appearance, but the reed modules in each are very similar:

<gallery widths=250 heights=187>
File:FMR-VR ReedCloseup.jpg                  | Fujitsu Magnetic Reed reed module
File:Omron B2R-M -- reed module removed.jpg  | Omron B2R series reed module
</gallery>

See:

*[[:Category:Reed switches|List of reed switches]]
*YouTube — [https://www.youtube.com/watch?v=ClvP1HqqxTI Actuating distances of Reed Switches having different Release AT (Drop-out)] (depicts different amounts of hysteresis)
*YouTube — [https://www.youtube.com/watch?v=5d0eRaMLzZs How does a bi-stable / latch reed sensor work?]