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{{TODO photo|more=true|not all variants are covered yet}} {{infobox dswitch | image name = RAFI RS 74 M.jpg | manufacturer = [[RAFI]] | product code = | contact mechanism = [[Metal leaf]] | switch type = Linear, alternate action, changeover | introduced = 1975<ref name="Intro" /> | discontinued = 2005 | family = [[RAFI full-travel key switch]] | keycap mount = [[RAFI mount]] | switch mount = [[PCB mount]] | travel = 2.5 mm | actuation force = 80 cN | patents = [https://google.com/patents/DE2504091 DE2504091] (1975)<br>GB1533154 (1976)<br>[http://www.google.com/patents/DE2914954 DE2914954] (1979) }} '''RAFI RS 74 M''' is a low-travel switch in the [[RAFI Full-Travel Keyswitch]] family. It is the mechanical counterpart to the Hall effect [[RAFI RS 74 C|RS 74 C]]. ==Description== RS 74 M switches share the same overall design as the 4 mm [[RAFI RS 76 M]] switch, but have a reduced travel of 2.5 mm. They are targeted at a [[unit]] of 0.75", or 19.05 mm, and the switch shells are themselves this exact width. The switch uses a square loop of sprung metal that is kept away from a metal contact by the slider. When the slider is depressed, the metal loop lowers until it reaches the static contact. The switch has two solder points, and the slider recess appears to form the single PCB fixing pin. Actuation is at 1.5±0.5 mm; the lug on the slider which raises the loop travels further than the loop drops. The sprung loop and the static contact both feature [[gold crosspoint]] contacts, as with most [[Cherry]] switches. The switches are available in several forms: linear, linear (illuminated), latching, and latching (illuminated). So-called "illuminated" switches simply have room for an [[LED]] in the top-right corner; they are not intended to provide backlit keycaps. RS 74 M was patented together with RS 74 C in [https://google.com/patents/DE2504091A German patent DE2504091A], filed in 1975. According to RAFI, RS 74 M was discontinued in July 2005.<ref>Conversation with RAFI, July 2013</ref> ==Key feel== RS 74 M switches appear to be intended for keypads, not desktop keyboards (for which, you would use the [[RAFI RS 76 M|RS 76 M]] or [[RAFI RS 76 C|RS 76 C]]); they have an actuation force of 80 cN within a pretravel distance of 1.5 mm, which makes them quite stiff. Based on a 1984 keyboard, they can also suffer from binding when struck at the corner. ==Keycaps== QWERTY keycaps are [[double-shot molding|double-shot]]; other legended keycaps are engraved and painted; RAFI's catalogue suggests that the engraving is not performed with a laser, as the infill process is not stated as being applied to lasered keycaps, only the "labour intensive" low volume engraving process. [[Relegendable key]]caps are also available. ==Variants== RS 74 M was covered in the 2001 Electromechanical Components catalogue, allowing some part numbers to be retrieved. Some switches have been discovered however were already end-of-life when that catalogue was published. Tentatively, the series appears to be divided as follows: *3.12960.nnnn — alternate action *3.12961.nnnn — momentary *3.17960.nnnn — illuminated {| class="wikitable variants-table" ! !! Part !! IP rating !! Type |- | [[File:RAFI RS 74 M SPST uncovered.jpg|175px]] || || IP40 || Momentary |- | [[File:No photograph.svg|175px]] || || IP40 || Momentary, illuminated |- | [[File:RAFI RS 74 M 3.12961.001.jpg|175px]] || 3.12961.001 || IP40 || Momentary, with increased ESD strength |- | [[File:RAFI RS 74 M red.jpg|175px]] || || IP40 || Momentary (red cover) |- | [[File:RAFI RS 74 M 3.12960.101.jpg|175px]] || 3.12960.101 || IP40 || Alternate action |- | [[File:No photograph.svg|175px]] || 3.17960.101 || IP40 || Alternate action, illuminated |- | [[File:RAFI RS 74 M SPDT latching.jpg|175px]] || || IP40 || [[RAFI RS 74 M SPDT latching|Alternate action changeover]] |- | [[File:No photograph.svg|175px]] || 3.12961.211 || IP54 || Momentary |- | [[File:No photograph.svg|175px]] || 3.12960.311 || IP54 || Alternate action |- | [[File:No photograph.svg|175px]] || 3.17960.351 || IP54 || Alternate action, illuminated |} ===IP40=== Standard momentary switches can be found with and without a clear plastic cover. The clear cover is depicted on type 3.12961.001, which has [[sealed terminals]] and is described as having "increased ESD-strength". The cover is non-conductive and appears simply to insulate the contacts. A variant with a transparent red cover has also been discovered; nothing is known about this version. The exact number of configurations is not clear. The basic unsealed momentary type supports two stationary contacts; a DPST/SPDT version has yet to be seen. Curiously, the SPST alternate action and SPDT alternate action variants have different part numbers moulded into the the bases (".374" and ".512" respectively) but these bases appear to be identical, supporting two stationary contacts. The momentary illuminated switch uses a different base where the top-right accepts an LED; this base also accepts a latching mechanism and will be shared with alternate action illuminated. All known sliders are white; the cream slider of the alternate action version depicted above is due to yellowing of the plastic. <gallery widths=250 heights=187> File:RAFI RS 74 M 3.12960.101 -- base.jpg | SPST alternate action base marked ".374" File:RAFI RS 74 M SPDT latching -- bottom.jpg | SPDT alternate action base marked ".512" </gallery> ===IP54=== The IP54 splash-proof variant was introduced in 1980.{{citation needed}} Instead of the clear top, it sports a diaphragm between the switch and its cap. An insert punches through the foil and connects the keycap with the slider.<ref name="Sealing" /> Illumination and alternate action are available in the IP54 sub-series. ==Keyboards== *Gercom portable unit (illuminated switches minus the LEDs)<ref>Reddit — [https://www.reddit.com/r/MechanicalKeyboards/comments/2duwxw/help_identify_switch_old_terminal_keyboard_project/ Help identify switch, old terminal keyboard *PROJECT*]</ref> *[[Neve Necam 96]] audio workstation keyboard *[[Siemens]] field programming unit 670 C (has the splash-proof variant){{citation needed}} *Thorn EMI Liberator keyboard<ref name="Liberator" /> ==Availability== RS 74 M switches were discontinued from production in 2005 but old stock was still available in 2013; in April 2015, RAFI confirmed that spare switches are no longer available. ==Gallery== <gallery widths=250 heights=187> File:Neve Necam 96 -- RAFI switches.jpg | RAFI RS 74 switches File:Neve Necam 96 -- RAFI switches angled.jpg | RAFI RS 74 switches File:RAFI RS 74 M -- PCB traces.jpg | PCB traces File:RAFI RS 74 M linear -- opened.jpg | Opened switch File:RAFI RS 74 M linear -- opened, rear.jpg | Opened switch viewed from the rear File:RAFI RS 74 M -- slider, spring, upper shell.jpg | Slider, spring, upper shell File:RAFI RS 74 M -- upper shell is hard to remove without damage.jpg | Upper shell is hard to remove without damage File:RAFI RS 74 M -- gold crosspoint prism on the static contact.jpg | Gold crosspoint prism on the static contact File:RAFI RS 74 M -- gold crosspoint prism on the sprung contact.jpg | Gold crosspoint prism on the sprung contact File:RAFI RS 74 M linear -- slider fully depressed.jpg | Slider fully depressed File:RAFI RS 74 M linear illuminated.jpg | Linear illuminated variant; the switch design is open and has no transparent top File:RAFI RS 74 M linear illuminated -- slider removed.jpg | Slider removed File:RAFI RS 74 M linear illuminated -- spring removed.jpg | Spring removed from the slider File:RAFI keycaps -- engraved vs double-shot.jpg | RAFI keycaps targeted at the RS 74 </gallery> ==Documentation== *[[:File:RAFI Electromechanical Components 2001, section 5, excerpt RS 74 and 76.pdf|RS 74 and 76 excerpt from Electromechanical Components 2001]] ==References== <references> <ref name="Intro">''Engineering Materials and Design'' '''19''' (1975) p. 77: ''The new Rafi RS74 keyboard system from Cole Electronics consists only of key switches and a printed circuit board — a matrix frame is not needed — giving low profile with an overall height of 15 mm.''</ref> <ref name="Liberator">The Register — [http://www.theregister.co.uk/2012/11/12/the_secret_history_of_liberator_the_first_british_laptop_part_one/?page=4 Liberator: the untold story of the first British laptop part 1] (page 4) Dated 2012-11-12. Retrieved 2015-08-01.</ref> <ref name="Sealing">Patent {{cite patent|country=DE|number=2914954}}. For a photo of the sealed switch, see "Rafi-System RS74, spritzwassergeschützt IP 54" in ''Konstruktion im Maschinen-, Apparate- und Gerätebau'' (1981), p. 169.</ref> </references> [[Category:RAFI switches]] [[Category:Keyboard switches with a RAFI mount]] [[Category:Low travel switches]] [[Category:Linear switches]] [[Category:Alternate action switches]] [[Category:Illuminated switches]] [[Category:Metal contact switches]] [[Category:List of all keyboard switches]]
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