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Cherry M9

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Overview

Cherry M9 was patented by Günter Murmann of Cherry Mikroschalter in 1979 (German patent DE2952107, subsequent English language patent US4339643 from 1980). According to Günter Murmann, the switches were designed for Triumph Adler’s electronic typewriters, and to use TA’s existing keycaps by way of custom keystems. This appears to confirm the “TA” in Cherry’s number system chart for M9. It also ties in with the switch appearing to be patented from the outset as double-action, which is a switch type generally only found (in keyboards) in typewriters.

He also reports that “Before we had MX available, we tried to use M9 for our own Keyboards with different keystem sizes”. It appears that Cherry designed the switches for both purposes simultaneously, because the first two keystem types numerically (1 and 2) are for standard Cherry 12 mm keycaps, with TA keystems taking higher numbers.

Examples in standard keyboards are extremely rare. A custom version of the switch—M94A-1GBR, with the same non-standard keystem as M51-0129/M51-0131—was used by IZOT (ИЗОТ) in their ES 8531 M2KL (ЕС 8531 М2КЛ) keyboard. Curiously this example was made in 1987, long after the M9 design was obsolete for keyboards. It is not known whether IZOT acquired surplus stock or whether this part was made specifically for them. Confusingly, these switches do not appear to take the same keycaps as IZOT’s reed switches. IZOT would also clone these custom M9 switches as IZOT 0125D (0125Д).

Configuration choices for this series include:

Subseries

Cherry M8 in Germany was divided into three subseries (M81, M82 and M84) according to the type of switch contacts used. Although no documentation has been discovered that names them as such, M9 also has four contact options: M91 through M94. The 1982 catalogue only lists M93, while the 1985 part number schema lists M92 to M94. No documentation exists that references M91, but boxes of M91A-11NN switches exist at Incotel Electronics in Lebanon; photos of these are shown below, provided by Incotel:

M91A-11NN box from July 1985
M91A-11NN box from August 1986

For some reason the part numbers on these boxes were wrong and needed correcting, in both the 1985 and 1985 batches.

The oldest visible date on the boxes at Incotel is only a few days earlier than the most recent date on the 1985 part number schema. The schema chart has a blank box where M91 could be listed. It is not clear if Cherry removed M91 from the chart after discontinuing it, or if they anticipated that M91 may at some point be produced and left a space for it. There is no information on when Cherry in the USA received that chart.

Specifications

Details on M9 are scarce. The only documentation comes from the Cherry Mikroschalter Keyboards and Switches Catalogue 1982, and the part number schema from 1985. See the M9 part number schema page for details.

The vast majority of M9 switches encountered are in typewriters, which appears to be the primary market for this series. Most if not all of the switches in typewriters are custom parts not listed in the catalogue.

General

Travel 4.2 mm
Pretravel 2±0.6 mm
Stage two operating point 3.5±0.5 mm
Bounce time 2 ms max
Lifetime 16 million (momentary)
5 million (alternate action)

Electrical

Note that the switching current limit for M93 differs between the 1982 catalogue (125 mA) and the 1985 part number schema (100 mA).

M91 is proven to exist, but no technical literature has been discovered for it.

Characteristic M91 M92 M93 M94
Contacts Ag Pd 30 solid prism Au 69 Ag 25 Pt 6 solid prism Au Ag 10, 3 µm plated wire
Switching current 100 mA 100 or 125 mA 10 mA maximum
Carrying current 500 mA
Voltage 60 V 28 V maximum 12 V maximum
Contact resistance 200 mΩ initial (typical 25 mΩ)

Variants

See the M9 variants page for details.

See also