Omron B3G-S series
Here follows a few notes on Omron B3G-S series mechanical keyboard switches and B35 series keycaps. Some of these notes relate to discussions with Sandy in 2015.
- “Flat” switches
- Moving click leaf patent
- B3G-S series catalogue entry (1986)
This translates to:
Key switch for B3G-S full keyboard (low profile type)
Low-profile type with an overall height of 18.1 mm suitable for DIN standards
- Despite its small size and low cost, it can provide the same feel as a high-end machine.
- Achieves reliability comparable to non-contact type by adopting dual-leaf crossbar contact mechanism.
- The jumper terminal structure (2 NO terminals) makes wiring on the board easy.
This two-finger contact approach was previously introduced by companies such as Marquardt and Mitsumi. The switch is specifically noted as being DIN-compliant, which is likely to be one of the reasons for the redesign.
Until I get around to posting a transcription of the whole document, here a couple of notes:
The page above only covers B3G-S100, B3G-S200 and B3G-S400. B3G-S300, which was not retained in B3G-S*N, is notably absent, and this possibly represents the latching variant, since Sandy notes that the later design no longer supports the latching guide frame. The higher numbers listed below (500 to 700) are also not covered.
The second digit covers “LEDスポット照光” (the presence of an integrated LED), being 0 (no LED), 1 (赤, red LED), or 2 (緑, green LED). For example, B3G-S220 would be S200 with a green LED.
“Flat” is Sandy’s nickname for the original design of B3G-S switch: the slider is a plain rectangle with notches in the corners, as seen on the 1986 catalogue page:
“Flat” switches are extremely rare, but two dated examples have been found so far, one from 1985 and one from 1987 (out of only four known instances of these switches). Sandy also possesses two latching “flat” switches (found in an NEC 8313-12 keyboard, and depicted by his photograph above), something not seen in the later design. (We are theorising that as the redesign did not allow for a latching mechanism, those few customers still requiring latching switches would continue to receive custom batches of the original design; latching switches at this stage were seldom used outside of Apple, who were not an Omron customer.)
“Non-flat” is familiar design of B3G-S where the front and back of the slider have cut-away recesses, and the opening in the switch shell has slits at the front and back: the front and back of the slider/opening design was modified to be similar to the sides of the slider and opening of Alps SKCL/SKCM switches.
Sadly, neither of us have yet determined more sensible names for these two design characteristics!
The history of B3G-S remains poorly understood. We know that in 1988, Omron issued PRDN 495, listing the part number correspondence between B3G-S and B3G-S*N. This occurred around the time that “flat” appears to have been superseded with “non-flat”.
- B3G-S to B3G-S*N part replacement (PRDN 495 1988-07-01)
The document is summarised thus:
Announcement of discontinuation of some mechanical key switch type B3G-S Series
A part of the mechanical key switch type B3G-S series will stop production.
The part replacement table (“生産中止機種と代替機種”) is given thus, with translations in parentheses:
|形B3G-S100シリーズ (B3G-S100 Series)||形B3G-S100Nシリーズ (B3G-S100N Series)|
|形B3G-S200シリーズ (B3G-S200 Series)||形B3G-S200Nシリーズ (B3G-S200N Series)|
|形B3G-S300シリーズ (B3G-S300 Series)||特殊対応 (Special handling)|
|形B3G-S400シリーズ (B3G-S400 Series)||形B3G-S600Nシリーズ (B3G-S600N Series)|
|形B3G-S500シリーズ (B3G-S500 Series)||代替機種なし (No alternative model)|
|形B3G-S600シリーズ (B3G-S600 Series)||形B3G-S600Nシリーズ (B3G-S600N Series)|
|形B3G-S700シリーズ (B3G-S700 Series)||形B3G-S700Nシリーズ (B3G-S700N Series)|
*外形寸法・仕様規格値の変更はありません。 / * Dimensions and specifications there is no change of the standard value.
The document also notes that “Manufacturing propriety of old products” is “impossible”.
So far, no documentation has been found that indicates what modification to the switch necessitated the change in part numbers, and whether this change occurred at the same time that the slider design was updated. A number of changes occurred around this time, including the removal of “JAPAN” from the switch shell, suggesting that the tooling had been shipped abroad. However, this occurred after the redesign from “flat” to “non-flat”, as the latter was seen briefly with “JAPAN” marking.
More dated examples of keyboards might give us better insight into this enigmatic switch series.
Amber Omron switches are generally seen with the word “JAPAN” deleted from the mould: that part of the mould has been ground away to remove the writing. However, this Focus keyboard (an FK-727, according to the controller marking) ca. late 1986 has Japanese-made amber switches.
|Date of notice:||1994-01-06|
|Date of discontinuation:||1995-03-31|
Moving click leaf patent
US patent 5015811 “Snap-action pushbutton switch with click sound” describes an alternative variant of B3G-S that uses a sliding click leaf (called a “plate spring”). Citing the typical click leaf design as prior art (redrawn from the Alps SKCM patent), the patent shows a new design with an inverted leaf that is pushed upwards by the slider. The slider bears a ramp that engages with the click leaf, and upon clearing the leaf, the leaf is fired upwards and collides with the top of the switch. The same action occurs when the switch is released, with the slider firing the leaf back downwards. Consequently this guarantees a tactile event and click sound on both press and release.
The patent does not appear to suggest why the leaf spring does not fall down after it has been fired upwards (it is depicted as remaining at the top of the switch), or why it does not deflect off the top of the switch. The spring is not loose when released, as the slider holds it down, but this is not the case when the switch is pressed, so friction alone would have to hold up the spring.
This patent was filed in 1988, which is likely to be after clicky B3G-S switches were introduced. No switches with this design have ever been seen.