Micro Switch SD Series

Honeywell Micro Switch
Hall Effect Switch
Manufacturer	Honeywell
Inventor	Everett A. Vorthmann; Joeseph T. Maupin
Switch type	Linear, Tactile
Sense method	Hall effect
Rated lifetime	Tested up to 30 billion; (extremely long)
Peak force	45 cN? to 320g

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A bunch of Honeywell Hall Effect switches and keycaps, Model 4A3A.

History

Introduced in 1968, Micro Switch (a division of Honeywell) adapted their Hall effect switch technology to work in keyboards. These switches are among the highest quality ever produced by any keyboard switch company, with reliability being paramount to their design. For increased reliability, there are both 3 pin and 4 pin designs of the switch, the later with dual sense lines for redundancy. The patent itself originates from 1969, but the design is aesthetically very different from the produced switches.

The Honeywell Hall Effect switch is most famous on some Symbolics keyboards, as well as the Space-cadet keyboard.

Features (as per Honeywell)

Details for switch Model 4A3A which should be consistent across all models, except for operating force:

Total Travel - 0.160 in (4.1 mm) nom.
Force at operating point - 2.8 oz. (78 g) nom.
Pretravel - 0.090 in. (2.3 mm) nom.
Release point at 5 VDC and 75°F (24°C) (With respect to free position) - 0.040 in. (1.0 mm) min.

Keyfeel

Smooth linear switch, makes Cherry MX Black switches feel like they have sandpaper on the stems.

Keycaps

Underside of Honeywell keycaps from the TI Telex 58SD17-2-B.

Top of Honeywell keycaps from the TI Telex 58SD17-2-B.

Triple shot for the LED windows of a keycap on a Convergent 64-00164 keyboard.

Honeywell Hall Effect keycaps are known to be exclusively double-shot, using very thick plastic in all cases.

Some keycaps have some odd properties such as this Caps Lock LED keycap (Switch Model 12B3S):

Lock keycap with an embedded red LED.
Underside of a Lock keycap with an embedded red LED.
Keycap mounting point for the Lock keycap with an embedded LED.

Availability

Honeywell hasn't been making these switches since the early 1990's and has been out of the keyboard business since then, so it's probably impossible to source them. Keyboards with the switches do show up occasionally on auction sites like Ebay, but this isn't always obvious, and they most certainly don't work with modern computers without a converter. The last known keyboard with these switches was made in mid 1996 for Sun Microsystems. Further research has shown that Honeywell has been using their "dual magnet" design to make backlit switches for industrial keyboards as recently as 1999. (Link)

Models

Angled B type Honeywell Hall Effect switches (mostly 4T3S), Convergent 64-00164.

White slider variants. The 1A8S has an extremely heavy weighting, 1A3S, is the standard weighting. TI Telex 58SD17-2-B.

While the switch isn't in production anymore, there were many variants of the switch, with a specific naming scheme to the models.

In almost all standard variants of the switch, there is a spot for a LED add-on part as seen in the Convergent 64-00164 keyboard.

Naming Scheme

As a regular expression, the models can be shown as such (not yet confirmed from Honeywell datasheets): ([A-Z])?([0-9]+)([A-Z])([0-9])([A-Z])

([A-Z])? Sensor variant? (All sensor PCBs with this code have this printed on it)
- Q - ?
- R - ?
- T - ?
([0-9]+) Switch variant
- 1 - White stem
- 4 - Black stem
- 5 - Black stem, locking mechanism
- 6 - Short black stem
- 11 - Black stem, tactile
- 12 - LED keycap stem
- 16 - Alternate keyboard mount (Link)
([A-Z]) Stem type
- A - Straight stem
- B - Angled stem
- F - No keycap stem
- T - Angled stem, ridged housing
([0-9]) Switch weighting
- 1 - Light (45g?)
- 2 - Mid (55g?)
- 3 - Normal (78g)
- 5 - Heavier (120g?)
- 8 - Heavy (320g)
([A-Z]) Switch type
- A - 4 pins, 2 [redundant] sense lines (Unknown difference from K,S)
- D - Dummy (no pins)
- E - 3 pins, 1 sense line
- K - 4 pins, 2 [redundant] sense lines (Unknown difference from A,S)
- S - 4 pins, 2 [redundant] sense lines (Unknown difference from A,K)