Micro Switch and Honeywell
- Keyboards history
- Product range
- Catalogue listing numbers
- Further reading
Micro Switch of Freeport, Illinois—typically written in capitals as “MICRO SWITCH” and commonly abbreviated to “Micro”—was one of the world’s first manufacturers of dedicated computer keyboards. 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 reed switch–based keyboards, Micro Switch introduced the world’s first solid state keyboards around 1968 with the Hall effect SW Series. This was succeeded by SD Series around 1975 or 1976, 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.
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.
Very little is known of early keyboard production. The oldest known involvement by Micro Switch in the keyboard industry is Series KB. Switches from this series show date codes going back to 1966. This series is listed in the 1973 manual switches catalogue, but the keyboard reed switch part of the series is given only a brief mention there. The series name of “KB” instead of “7” does imply that the keyboard switches were originally the primary goal for the series. It may be that the reed keyboard switches had been sidelined by 1973 in favour of the solid-state switches, or it may be that Micro Switch simply preferred to supply fully-assembled keyboards (under RW Series) and covered these wholly in a separate brochure or catalogue.
The RW Series reed-based keyboards are very rare, and only seem to date from 1970. Previous keyboards using Series KB switches appear to have been assembled by the computer manufacturers using switches bought from Micro Switch. These too are rare.
Series KB seems to have only been current for a brief period (as little as two years, if they were introduced in 1966) before Micro Switch introduced Hall effect solid-state switches and keyboards in the form of SW Series in late 1968. SW keyboards are much more commonly found. 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.
Around 1975, Micro Switch redesigned their Hall effect switches to produce SD Series. 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.
Switches and keyboards
- Series KB switches
- RW Series reed switch keyboards using Series KB switches
- PB Series switches (of which a small subset can be used in keyboards)
- SW and SN Series Hall effect switches and keyboards (so called “dual-magnet” switches)
- SD Series Hall effect switches and keyboards (“Honeywell Hall Effect”)
- SC and ST Series membrane keyboards
- RX Series rubber dome over membrane keyboards
- WN Series rubber dome over membrane 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.
- 2SW Series: double-shot keycaps used with SW, SN and SD Series switches
- CT Series low-profile double-shot keycaps
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.