Cherry M8, MD and MJ
Serie M8 is an ultra-low-profile keyboard switch series from Cherry in Germany, offering 2.5 mm travel. German M8 is fairly well documented: see the M8 schema for details. Standard German M8 switches use the 6 mm keycap mount, which is effectively a shorter version of the 8 mm mount used on Cherry MX. Variants were also available that accepted 12 mm keycaps. Hirose Cherry Precision in Japan ran their own M8 product line; Hirose M8 switches used their own contact system and accepted Hirose keycaps. Hirose also introduced MD and MJ series in 1983 that extended the travel to 3 mm and 4 mm respectively, with corresponding increases to the height of the switch body.
German M8 was divided into three subseries—M81, M82 and M84—according to the type of switch contacts used. M81 and M82 use solid metal contact prisms with gold and silver alloy contact surfaces respectively. These metal prisms were expensive to manufacture, and shortly after the introduction of Cherry MX, Cherry introduced a new lower-cost contact type based on gold-plated wire. This new contact type was introduced to M8 switches as subseries M84. M83 was used by Hirose for their switches, using their own contact arrangement.
German M8 switches offered the following configuration options:
- Single or double pole configuration
- Linear or one of two strengths of tactility
- Optional LED illumination
- 0° or 7° keystem angle
- Higher weighting for space bar
- Open-top shell for minimum height or enclosed shell for dust protection
- Keystem for 6 mm or 12 mm keycaps
- Choice of solid gold alloy, solid silver alloy or gold-plated switch contacts
M8 was not patented: initially Cherry did not consider it necessary, which they came to regret. This means that the age of M8 cannot be determined from a patent. Peter Cherry suspected that the series was introduced around 1976 or 1977, whereas Günter Murmann suggested 1981 or 1982, on the basis that he feels that it came out perhaps a couple of years before MX. Cherry in Germany provided a copy of the numbering system chart for M8, drawn (“gez” denoting “gezeichnet”) in 1981, but appearing to replace an older document of the same number (“gl.Nr.”, “gleich Nummer”) from February 1979. No advertisements or marketing material have been found that cover the introduction of M8. With the MX numbering chart originally drawn around a year before MX’s introduction, M8 could have been introduced as late as 1980 or 1981 without contradicting the dates on the chart.
In Evaluation Engineering in 1979, the following was written in an unspecified article somewhere within volumes 18 to 18, partially available on Google Books:
During the past year, the German facility of Cherry Electrical Products has been developing a low-profile key-module, the M8 Series, using similar construction and the same ‘‘gold cross-point’’ contacts also used in Cherry’s standard M61 and its German M71 key-modules.
The remainder of the paragraph (if any) can only be unlocked if one can guess what words appear in it, and it does not indicate when the series became available, but it would appear to be no earlier than 1979.
Cherry issued an end-of-life notification for M8 on the 31st of July 2013, and set the 31st of October 2013 as the last-buy date. A small quantity of M84A-0100 was obtained for Deskthority by Robin Bithrey of Cherry UK, while 20 models remained available up to that date. Only M82, M84, and M85 (a different but related series) were available by this point, with M81 being already discontinued.
Note that the contact bounce time differs between the 1982 catalogue (2 ms) and the various M8 brochure scans, all of unknown age. Bounce time was not given in the 1998 catalogue.
|Pretravel||1.6±0.6 mm (linear)|
|1.3±0.6 mm (regular tactile)|
|1.4±0.6 mm (German postal tactile)|
|Bounce time||2 ms max (M81, 1982) or 5 ms max (brochure, all types)|
|Lifetime||10 million (momentary)|
|Contacts||Au Ag 26 Ni 3 solid prism||Ag Pd 30 solid prism||Au Ag 10, 3 µm plated wire|
|Switching current||100 mA maximum||100 mA maximum||10 mA maximum|
|Carrying current||500 mA|
|Voltage||28 V maximum||60 V maximum||12 V maximum|
|Contact resistance||200 mΩ max. initial (typical 25 mΩ)|
Hirose Cherry M8
Separately, Hirose Cherry Precision in Japan made their own versions of M8 switches. These are themselves divided up into two separate subseries, M83A and M83S. Unlike German switches which were linear by default, Hirose M8 switches all seem to be tactile, although this was not advertised on the datasheet. Hirose Cherry provided a datasheet covering M8, MD and MJ, which they do not permit to be shown here.
The relationship between German-made M93 and Japanese-made M83 is not known. Japanese-made M8 switches use Hirose’s own contact form, using a through-hole copper (or copper alloy) base plated in gold alloy, which stands in stark contrast to their datasheets which depict a structured solid alloy identical in form to that of American-made switches. However, the contact alloy used by M93 matches the composition of Western Electric Alloy #1, which is the alloy that Hirose claim to have used. The alloy itself is not sufficient to define the characteristics of a switch, as the contact construction as a whole needs to be taken into account.
Switches with the Hirose planform but with German M81/M82–style contacts have been found in the German-made Basis 108 microcomputer keyboard, used for the unstabilised wider keycaps. The keystem however is German-style, suggesting that these special switches were moulded afresh in Germany. This type is not given in the M8 brochure. The encoder seems to be from week 34 1982.
Pale pink plungers have been found by パンミア (rzwv) in the keyboard of a SORD M23 computer. These switches look as though they use German-style triangular prism contacts as with the Basis 108 keyboard, the design that Hirose themselves claimed to use in their datasheets. Unfortunately パンミア has not provided any way to determine the age of that unit.
M83A appears to be the standard Japanese M8 switch. These switches exhibit a number of differences compared to their German counterparts. The most notable is the plunger planform, which appears to be designed for increased stability. This prevents an LED from being placed centre-edge as in German switches. Instead, the switch accommodates a miniature 2 × 4 mm rectangular LED in the rear-left corner. Travel is 2.5 mm as per German M8 switches.
M83S is the same size as M83A, but it reduces switch travel from 2.5 mm down to 1.5 mm. The raised areas on either side of the plunger are omitted. These switches so far have been found with black plungers. These have been found in the Epson PX-8 (for the function keys) and Yamaha QX21. In the former case, they are fitted with dust covers, unlike the MD switches used for the other keys.
Hirose Cherry MD and MJ
Hirose also produced two related series, offering greater travel. MD series extends the shell height from 6.7 mm to 7.3 mm, and the total height from PCB top surface to the top of the keystem by 0.5 mm from 10.6 to 11.1. Travel is increased to 3 mm. MD switches with angled keystems were used in the Epson PX-8, although keystem angle was not a documented feature on the datasheet. MJ series extends the shell height another 0.4 mm to 7.7 mm, and the total above-PCB height by 0.6 mm to 11.7 mm, providing a full 4 mm of travel. MD and MJ were mentioned on the chronology/milestones page of the former Hirose Cherry website:
|昭和58年4月||低背形キースイッチ(MDシリーズ)発売。||April 1983||Low-profile keyswitch (MD series) was released.|
|昭和58年4月||低背形キースイッチ(MJシリーズ)発売。||April 1983||Low-profile keyswitch (MJ series) was released.|
The datasheet that covers M8, MD and MJ is not clear. All three types are shown with the Hirose M8 slider planform, but the M8 drawing appears to show a regular MX-style keystem. MD and MJ are shown with Hirose keystems. The keystem details are not clarified for any variant, but all types are shown with the shorter 3.5 mm keystem.
In summary, the types are as follows:
|M83A||2.5 mm||6.7 mm|
|M83S||1.5 mm||6.7 mm|
|MD||3 mm||7.3 mm|
|MJ||4 mm||7.7 mm|
Shell height includes the stand-off nubs, i.e. it is the distance from the top of the shell to the top of the PCB.
The Epson PX-8 computer used MD switches, with M83S used for the top row (Esc through PF5).
See the M8, MD and MJ variants page.
- Nummern-System Flachtaste TS-00001 (M8 part number system, 1982-02-02; scanned by Cherry in Germany)
The Hirose Cherry M8 datasheet cannot be made publicly available unfortunately.