Micro Switch SD Series

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Micro Switch SD Series
Manufacturer Micro Switch
Inventor Everett A. Vorthmann
Joeseph T. Maupin
Supersedes Micro Switch SW Series
Switch type Linear, Tactile
Sense method Hall effect
Rated lifetime Tested up to 30 billion
(extremely long)
Peak force 45 g to 320 g[Citation needed]


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 4 pin are +5, GND and dual open-collector outputs, allowing wired-or of the X, Y keyboard matrix. These switches are naturally bounce-free!

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

The last accessible reference to SN and SD series on the Honeywell website is from the 22nd of February 1999.[1] The products list at this time were:

  • Hall-Effect Keyboards Sales Sheet (02509_a.pdf)
  • SD16 Keyswitch Modules Product Sheet (02503_0.pdf)
  • 63SD30-4 Microcomputer-based Keyboard Product Sheet (02504_0.pdf)
  • 26SD1-2 Point-of-Sale Keyboard Product Sheet (02506_0.pdf)
  • 12SD/16SD Numeric Keyboards Product Sheet (02607_0.pdf)

The PDF documents were not archived. Later that year, Honeywell redesigned their website such that it could no longer be crawled (product data was accessible through form submission), so it is not clear when SD and SN series were phased out.

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.

Note that according to the 1998 1001SD Series Chart 2 (listed within Micro Switch SD16 Keyswitch Modules, below) this should be 0.695 N/2.5 oz, so the specifications may have changed over time.

Key feel

Linear switch, much smoother and consistent in feel than Cherry MX Black switches for example.


There are 26 confirmed variants of the switch, probably more unknown variants exist. For a detailed view of the inside of these switches please refer to dorkvader's Hall Effect Switch Compendium linked at the bottom of this page under the external links.

Part numbers

Micro Switch and Honeywell switches typically have the series name within the part number, which was apparently notably not the case for SD Series. According to the 1998 1001SD Series Chart 2, the part numbers are are of the form 1001SDnnnn, where the four-character "identification code" is all that is printed on the switch, for brevity.

As a regular expression, the models can be shown as shown below. Descriptions given in italics are observations not corroborated with Micro Switch documentation.

According to the datasheet, "sloped" switches have upright stems: the description refers to how a tilted keyboard the keycap top surfaces will be sloped. Angled stem switches are called "stepped" due to the presentation of a staircase profile in a tilted keyboard.


  1. ([A-Z])? Sensor variant? (All sensor PCBs with this code have this printed on it)
    • D - ?
    • Q - ?
    • R - ?
    • T - ?
  2. ([0-9]+) Switch variant
    • 1 - Unknown (white stem)
    • 4 - Momentary action (black stem)
    • 5 - Alternate action (black stem)
    • 6 - Support (short black stem)
    • 11 - Black stem, tactile
    • 12 - LED keycap stem
    • 16 - Alternate keyboard mount[2]
  3. ([A-Z]) Stem type
    • A - Sloped (non-angled)
    • B - Stepped (angled)
    • F - No keycap stem
    • G - Flat top
    • H - Flat-stepped
    • K - Narrow bar stem
    • S - Sloped
    • T - Stepped (ridged housing)
  4. ([0-9]) Switch weighting (hard to read in the datasheet; some figures are best guesses)
    • 1 - 0.362 N/1.1 oz
    • 2 - 0.556 N/2.0 oz
    • 3 - 0.695 N/2.5 oz
    • 5 - 0.973 N/3.5 oz
    • 6 - 1.668 N/6.0 oz
    • 8 - 2.224 N/8.0 oz
    • 4 - No spring (use with three unit button)
  5. ([A-Z]) Switch output
    • A - Sink level (4 pins, 2 redundant sense lines)
    • B - Sink pulse
    • C - Source level
    • E - 3 pins, 1 sense line
    • K - Timed repeat (4 pins, 2 redundant sense lines)
    • S - Logic scan (4 pins, 2 redundant sense lines)
    • D - None

Known variants

Confirmed variants of the switch:


SD Series appears to have gone out of production around 1999 or 2000. 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.[Citation needed]

Electrical characteristics

Sense circuit schematic for a Honeywell Hall Effect switch Sense circuit current sinking profile

Controller sensing characteristics

Sense circuit schematic for a Honeywell Hall Effect switch Sense circuit current sinking profile

Switch dimensions

16SD3-5 Hall Effect Keypad schematic, top view 16SD3-5 Hall Effect Keypad schematic, side view, keytops 16SD3-5 Hall Effect Keypad schematic, side view, no keytops


External links


  1. Internet Archive Wayback Machine — Hall-Effect Keyboards (1999-02-22)
  2. MouseFan — SUN 32SD38-4-E USA (Japanese only) Last updated 2004-05-02. Retrieved 2015-07-27.