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Micro Switch and Honeywell



Micro Switch of Freeport, Illinois—typically written in capitals as “MICRO SWITCH” and commonly abbreviated to “Micro”—was an early entrant to the computer keyboard market, with keyboard switches entering production somewhere in the early 1960s. The company was founded in 1937 to produce the then recently-invented “micro switch” (being a trademarked term). Honeywell would later purchase the company in 1950; for its entire time as a keyboard manufacturer, it was a division of Honeywell. Following on from mechanical and reed switches and keyboards, Micro Switch introduced the world’s first solid state keyboards around 1968 with the Hall effect–based SW Series. This was succeeded by SD Series in 1975, also Hall effect. Honeywell continued to advertise Micro Switch solid state computer keyboards and switches through 1999, which is the last known instance of these products. Their product range also encompassed conductive and capacitive membrane keyboards, as well as straightforward rubber dome keyboards.

According to Larry Bishop, a long-time employee who spent 12 years in quality engineering with the Solid State Keyboards group, Honeywell were a great parent organisation who permitted Micro Switch to run as a separate company, and the organisation as a whole was “One Huge Family”. Engineering resources were provided by Honeywell to improve the solid state sensing technology. He cites keyboard production as 1000 per month.

Honeywell itself (now Honeywell International) dates back to 1906, as the Honeywell Heating Specialty Company. Honeywell produced lower-end keyboards under its own name in the 1980s and 1990s, before selling off keyboard production. Production of WN Series rubber dome keyboards was licensed to Siam United Hi-Tech (SUH) during the period 1990–1994, during which time they were produced under licence by SUH as SUH-Honeywell. Keyboard production in Mexico (including WN Series) was sold to Key Tronic in 1993. Michael R Bonsignore, who was the Honeywell CEO at the time, said that “Honeywell’s keyboard division has been profitable but no longer fits with company plans to focus on systems controls.” The acquisition cost around $30 million, and had completed by the beginning of August 1993.

It seems that the Honeywell brand continued to be used. Key Tronic model E03601ELHW-C was found with Honeywell branding in addition to the Key Tronic name.

In 1999, AlliedSignal bought Honeywell, and (according to Larry Bishop) moved basic switches to Mexico, solid-state sensors to China and engineering to Bangalore in India. This is the same year in which the website was redesigned and the same year as the final date on the SW Series charts, although not necessarily for the same reasons.

Keyboards history

Very little is known of early keyboard production. The oldest known involvement by Micro Switch in the keyboard industry is KB series. The self-encoding switches from this series date back to 1964, and reed switches followed around 1965 or 1966. “Mechanical” keyboards with KB switches were introduced later circa 1967, and the “Phase II” reed switch keyboards followed in 1967 or 1968, under RW Series. (There is some disagreement with the presently available information as to the exact years of introduction.) The series name of “KB” instead of “7” does imply that the keyboard switches were originally the primary goal for the series.

In late 1968, Micro Switch introduced Hall effect solid-state switches and keyboards in the form of the “Phase III” SW Series. SW keyboards are much more commonly found than the older KB and RW keyboards. One significant change with SW Series is that, while still mounted into metal bars, SW switches snap into place, making assembly and disassembly much quicker than with KB switches, which must each be separately secured with two screw clamps.

SW Series is much better understood, and is known to have offered a wide variety of options, including alternate action, centre illumination, secretarial shift, double action (“bi-level”) and apparently also tactile feedback.

Somewhere around the late 60s, Micro Switch also introduced clicky mechanical switches built around SM Series microswitches; these were placed into the larger PB Series. These PB keyboard switches are even rarer than KB switches. The most interesting aspect of PB keyboard switches is their mechanical one-shot mechanism, which releases the switch contacts immediately, so long as the operator does not tease the switch by holding it at the point between microswitch actuation and where release is triggered. This appears to be a means to achieve N-key rollover without diodes.

In 1974, Micro Switch redesigned their Hall effect switches to produce SD Series; commercial availability appears to have been 1975. SD Series switches are smaller, and fit into a metal mounting plate. SD Series keyboards were hugely successful. The most recent example discovered to date is a Sun Microsystems 32-key keypad, made in 1996. SD Series was still advertised on the Honeywell website as late as 1999, around 24 years after the series was introduced. SD Series keyboards and keypads are widely available second hand. (SN Series Hall effect switches were also still advertised in 1999.)

In parallel, Micro Switch and later Honeywell also produced a number of membrane-based types, starting with keyboards with discrete plate-mount actuators, and finishing off with simple rubber dome keyboards.

Yamatake Honeywell

The brief information on the Honeywell website about Honeywell Japan Ltd mentions “Yamatake Honeywell JV” in 1953 at the start of the timeline, suggesting the commencement of a joint venture. One keyboard from Yamatake Honeywell is known, 100SW5-3J2661A from April 1984. There are no close-up photos of the switches, so thus no way to check for indications of whether the switches were made in Japan or sourced from the US. The switches appear to be largely 1SW51, based on the red plunger colour and straight keystems. A Yamatake-Honeywell SD Series keyboard with catalogue listing 76SDU-3J1612 can be seen in the NEC Spinwriter 7720 printing terminal; this example was manufactured in “7-82NT”, likely July 1982.


Final assembly and testing of some keyboards took place at Dörnigsheim, a location owned by Honeywell Bull, according to Larry Bishop. Switches and populated PCBs were supplied from the US factories. Only two such keyboards are presently known: an ICL 2903 mainframe keyboard from 1974 (84SW11-4) and a Decision Data 8010 keypunch keyboard from 1975 (54SW11-19).

Product range

Switches and keyboards

KS Series switches (such as 1KS1-T and 1KS3-T) could potentially be usable in keyboards, but this has never been observed, and it seems unlikely that they were ever used as such.


Catalogue listing numbers

There are at least two prominent part number (“catalog listing”) formats. Numbered series (e.g. Series 2, Series 3, Series 6) have catalogue listing numbers that begin with the series number, which is followed by a single sub-classification letter. The rest of the code is formed from both letters and numbers. For example, switch 3A14A denotes Series 3 (“3”), power switch with matrix mounting subcategory (“A”), one form X with one lamp circuit (“14”) and black housing without barriers (final “A”). The length and format varies considerably and is completely series-specific; catalogue listing 4A22BMA91 denotes Series 4 (“4”), switch (“A”), barriers and mounting clips on the short sides (“22B”), SPDT-NO alternate action with 10-amp silver contacts (“MA”), and no lamp socket (“91”).

Most series used two-letter alphabetic names. Catalogue listing numbers for these series have the curious property that the series name is enclosed on both sides by the remaining characters. Subclassification is handled by placing a numeric prefix in front of the series name. For example, in SN Series, the prefix can be one of 11 (snap-in panel mount), 101 (PCB-mount non-illuminated) or 201 (PCB-mount illuminated). For example, catalogue listing 11SN1B2 denotes snap-in panel mount subcategory (“11”) within SN Series (“SN”), standard momentary switch (“1”), sink pulse Hall sensor (“B”) and pre-installed incandescent bulb (“2”). With PB series, the prefix is frequently a combination of the number of poles and other characteristics, e.g. prefix “3” denotes three-pole momentary, while prefix “83” denotes three-pole alternate action. For keyboards, the prefix number indicates the number of keys. For example, a catalogue listing beginning “2SW” indicates an SW-series keycap, while a catalogue listing number beginning “12SW” indicates a 12-key keypad.

Series KB is an exception, with part numbers that indicate that it is Series 7, but the series name is alphabetic.

Certain keyboards follow a non-standard pattern. These have long prefixes in front of a more typical-looking catalogue listing that lacks its suffix codes:



Further reading