Micro Switch KB
- See also
KB was a series of pushbutton switches from Micro Switch, that also contained the associated indicator units, buttons and connector blocks. It sat in a family alongside Series DS miniature display switches and Series 3 power and reed switches, all of which assemble into strips by way of mounting frames. A photograph of a Series 3 switch in Electronic Design Vol. 21 No. 10 (10th of May 1973; page 27, PDF page 31) shows how similar the two series are.
The series provided both mechanical and keyboard reed switches. The reed switches from this series were briefly used in keyboards, including RW Series from Micro Switch. The mechanical switches support output encoding, alternate action, illumination, tactile feedback and mechanical interlock, and there are models suitable for power switching. The feature set of the reed switches is not known as no documentation for them has been found.
In the 1973 catalogue, the name “Series KB” is used in the table of contents, but the section for that series calls them only “KB”, as does all other literature discovered to date.
KB part numbers are anomalous. All the part numbers begin “7”, as though it were Series 7. The part number pattern follows those of actual numeric series, such as Series 2 and the closely related Series 3.
KB is also one of only two types found to have symbol codes stamped onto some switches.
The earliest mention of the series is from Information Display, January/February 1966 (page 14, PDF page 12), where they are described as “NEW MICRO SWITCH KB”. The reed switches are not mentioned in the advertisement. Promotional material from 1966 to 1969 (see under Documentation below) also omits the reed switches, even though they are confirmed to have been in production since the end of 1966, based on manufacture dates stamped onto the switches. Dates on KB switches in general have been found ranging from 1966 to 1982.
The series was present in the 1973 manual switches catalogue (Catalog 51 issue C), but was absent from the 1988 manual switches catalogue, Micro Switch Catalog 30 Issue 8. This latter document includes Series 2, 3, 4 and 6, but lacks both Series KB and Series DS, suggesting that KB had reached end of life by that time.
Keyboards using these switches have so far only been found in the 1966–1970 timeframe; KB reed switches were swiftly replaced with SW Series solid state switches for keyboard purposes, which former Solid State Keyboards staff member Larry Bishop confirms.
KB switches are mounted together in rows into pairs of metal bars. The top edge of each bar has regularly spaced notches; a small ridge around 2.25 mm wide on one side of the switch locates it within the bar. The top of the switch has overhanging ridges that sit around the mounting bar, and each switch has two threaded rubber pieces with corresponding ridges that secure the switch to the bar from below. The lower grips are pressed against the bar by turning the screws on which they are placed. Each row in turn appears to be attached to the keyboard by way of narrow modules that attach to both the bar and the top case.
The illustration below is only approximate, as dimensions were taken only from a single loose switch.
Series 3 mounting bars come under subseries 3M. Catalogues only depict 3M1 full-height bars; the short bars for direct wiring is 3M2. KB shares the mounting bar system from Series 3. Mounting bars also exist in KB, under subseries 7E.
There are at least three keycap families used with these switches. One of them is 2SW Series or a derivative thereof, which was revised to fit special wide keystem adapters; these are seen in RW Series keyboards. There were also slot-mount keycaps similar to those found on IBM beam spring switches, found so far in a single keyboard. A third type, using circular raised areas on square blocks, also used the slot mount. The 1973 catalogue does not give the keycap series name; it only notes that a truncated form was chosen.
Keycaps cannot be attached directly to KB reed switches. The switch itself has a slot mount, that is a combination of two overlaid slots around 1.1 × 2.2 mm, one at 0° and one at 90°. A flat metal adapter is placed into this slot, bearing the desired keycap mount. It appears that at least two such adapters exist: a narrower one that fits older keycaps, and a wider one that takes specially-modified 2SW Series keycaps.
Many switches appear to have a simple hole in the keystem, without the slots. Examination of 7A1H-X55 shows that there are small ridges on the inside that serve to define the slots. The shape is something similar to this; the image is only a suggestion as the details are too small to photograph or measure:
In other examples, these do not appear to exist at all, but there are no photographs clear enough to be certain, and there is likely to still be something within the hole to ensure correct orientation of the keystem adapter.
Within the switch there is a flat plastic frame which sits above the return spring and holds one or two cylindrical magnets. This frame may extend out to form the intermediate keystem. The intermediate keystem can also be a separate part that presses onto the magnet frame. This has been shown to be removable, but with 7A1H-X55 it cannot be removed without excessive force and damage.
The same general style of adapter system appears to be used with 1KS switches, being observed in 1KS1-T and 1KS3-T (which look identical).
Some keyboards with KB switches do not have a PCB for the switches. Instead, the switches are all connected via flying leads. Here, the flat terminals on the switch permit the use of spade connectors for solder-free attachment. These switches do not have stand-offs.
For keyboards where the switches are soldered to a PCB, normal PCB solder terminals were used. The terminals are wider just where they protrude from the switch; this short wide area appears to serve as a stand-off.
The non-reed switches are designed for socket connection via connector blocks, which are special sockets that separate out the wiring from the switches. Such switches can be extracted from the control panel or keyboard and replaced without the need to desolder the failed switch.
KB reed switches are capable of single and double pole configurations. Some switches have the holes in the base for the second pair of terminals (and for additional terminals of unknown purpose), while others have a shell that only accepts a single-pole configuration.
No double-pole reed switches have yet been observed.
|7C*||Indicators (lamp-only units)|
|7D*||Connector blocks, which are sockets for the switches that keep the wiring connections separate from the switches|
|7E*||Mouting bars, mounting blocks|
|7G*||Half-unit spacers, lugs, screws|
The fourth character in the part number indicates the switch grouping. Non-reed types include:
|7A1A*||Encoding switches||Various||1 unit|
|7A1C*||Illuminated non-reed||Double||1 unit|
|7A1D*||Illuminated non-reed||Single||1 unit|
|7A1E*||Illuminated non-reed||Quad||1.5 unit|
|7A1G*||Illuminated non-reed||Double||1.5 unit|
|7A1H*||Reed switch with hand-wire terminals (unconfirmed); possibly H for hermetically sealed contacts||Single (unconfirmed)||1 unit|
|7A1M*||Reed switch with PCB terminals (unconfirmed)||Single (unconfirmed)||1 unit|
The following reed types have been discovered to date. Presently no documentation has been found that covers them, and the differences between some of the types remains a complete mystery.
|Catalogue listing||Type||Shell colour||Plunger colour||Configuration||Terminals||NSN||Observed dates|
Illuminated panel buttons
The following models are given in the 1973 catalogue:
Other switch types
The following types are not in the catalogue, and have not been inspected closely.
|7A1AA||Six sets of terminals; found dated 6952 (eBay)|
|7A1AH||One set of terminals, with long trombone protrusion from base (eBay, 6631)|
|7A1CG||Similar to 7A1CA, but with the trombone (eBay, 7442)|
The following table lists keyboards made by Micro Switch customers using KB switches. For Micro Switch’s own keyboards, see RW Series.
|Burroughs D8565 keyboard||7A1HA, 7A1H-X27, 7A1H-X4||ca. 1968|
|Mohawk Data Sciences keyboard||7A1H-X17, 7A1H-X18||ca. 1966?|
|Unidentified keyboard||7A1HS, 7A1CA||ca. 1970?|
The Micro Switch Catalog 51 excerpt was provided by the National Museum of American History Library (part of the Smithsonian Institution). The PDF of promotional material was scanned in by the Computer History Museum, and is (apparently despite their best efforts) low resolution and out of focus. No documentation has been found that covers the reed keyboard switches, however.
- Micro Switch KB promotional material (1966–69)
- Micro Switch Catalog 51 issue C section D (March 1973), covering Series DS, Series 3 and Series KB
- Micro Switch magnetic reed page on the Deskthority wiki