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Micro Switch SW Series

Contents

Overview

SW and SN are Micro Switch’s original series of Hall effect pushbutton switches.

Micro Switch Solid State Keyboards used SW series switches. These switches clip into rail trays in the keyboard that sit atop the PCB. These trays have a line of clips on each side to secure the switches, the lower locating nubs for each return spring, and holes to allow the terminals of Hall sensors to pass through to the PCB. Micro Switch give the reason for this arrangement as being a way to prevent keystroke impact from reaching the solder joints on the PCB. In effect, these trays function very similarly to mounting plates, but they support the switches from below instead of from the side or top.

SW switches are open at the bottom, and when removed from the keyboard, the Hall sensor remains in the keyboard. The return spring is not part of the bill of materials for the switch: the switch models cover only the physical design and choice of Hall sensor. When sold separately, the spring is included, and these parts have separate numbers indicating that they are replacement modules and—for models with a spring weight other than the default of 3 ounces—the weight of the included spring.

Micro Switch also provided a line of self-contained switches with sealed bases. These SN switches could be snapped into a panel, or attached directly to a PCB, depending on the model.

Design

SW Series switches are all open at the base: nothing holds the return spring inside the switch, and the Hall sensor is a slide-in fit. These switches clip into securing rails fitted onto the keyboard matrix PCB. The design rationale is not known, but a likely explanation is serviceability. Since the switches are contactless, they would typically only need servicing to replace a fouled housing or broken plunger. In such cases, there would be no need to supply or replace an expensive Hall sensor: all that is needed to replace a broken switch is to swap out the housing assembly, without the need for any desoldering. With that said, replacement switches do come with a fresh Hall sensor when purchased separately.

In the 1968 advertisement, the plungers were grey. In later years, different colours were used (as documented by Micro Switch). It seems that black was more common in early years, with colours added later. Leaflet PK 8503 2 shipped with replacement module 1SW51-R cites an additional plunger colour, of grey, which has a different internal design. The diagram in the leaflet is not clear enough to understand the difference; it is simply a guide to seating the return spring during switch replacement. This may relate to the grey plungers shown in the 1968 advertisement.

Options

N-key rollover

N-key rollover in SW Series keyboards is achieved by allowing each switch to only conduct electricity for 50 µs. This is achieved using the sink pulse Hall sensors. By the time that a second key is pressed, the first key should have already stopped conducting, and there will not be two keys conducting electricity at once. As such, even if the first key is held, it is no longer detected. With only one key active at a time, current cannot pass the wrong way through the switch.

The consequence of this decision is that it is not possible to detect whether keys are held or when they are released. Modifier keys use sink level or source level Hall sensors so that key press and key release can be detected separately.

Key repeat

Key repeat in SW keyboards was achieved using a strobe pin (STB) on the connector. This strobe output instructs the host equipment to apply repeat to the last keys depressed. There were at least three ways to enable the strobe output:

Product Brochure SW reported that Honeywell’s Systems and Research Division found that use of N-key rollover reduced operator error by up to 30% over 2-key rollover.

Lock keys

Lock keys are achieved using one of the following methods:

Models

Product and part numbers are divided into two main groupings. Components use catalogue listings of the form “SW-” followed by five digits. This grouping includes magnets, shells, plungers, “spacers” (pry tools), PCBs, sensors etc. Switches and complete keyboards have catalogue listings where “SW” is prefixed by a number.

Grouping Usage
1SW… Switches
500SW… Uncertain; includes 500SW90-3, which is a sealed keyboard plunger
Other nSW… Keyboards
SW-nnnnn Components

Switches

Schema

The part number schema for SW Series switches is as follows:

1SWM(-R(F))

“1”
Prefix for keyswitch modules (higher numbers indicate keyboard with that number of key stations)
“SW”
Series name
M
Model number, in a range of at least 1–301
“R”
Denotes a replacement part
F
Operating force in ounces; where omitted, the operating force is the default of 3 oz

Subseries

Switches in SW Series fall into at least two subseries:

Subseries Range Type Numbering
1SW Series 1SW1–1SW99 Non-illuminated Odd sloped, even stepped
1SW100 Series 1SW100–1SW199 Illuminated Unknown
1SW200 Series? 1SW200–1SW299? Unknown
1SW300 Series? 1SW300–1SW399? Unknown

1SW1 Series switches appear to exist in pairs, with each odd-numbered model having a straight keystem for sloped keyboards, and each even-numbered model having an angled keystem for stepped keyboards.

1SW100 Series switches are not fitted with lamps: unlike 201SN Series, there are not pairs of part numbers depending on whether a lamp is fitted.

No useful data remains on 1SW300-R and 1SW301-R.

The allocation of part numbers to double action and secretarial shift types is not known.

Models

1SW Chart 1 lists a large number of models, but omits most product details. Known models are listed below.

The “R” suffix indicates a replacement switch sold separately in a box along with an instruction leaflet, return spring and two “spacers”, which are the pry tools used to extract a failed switch. The digits that follow the “R” are not explained, but they appear to indicate the weight in ounces of the spring supplied in the box; they are only seen on “R” models. “1.5” is a half force switch, used together with a support switch on wide keys; “2” would be 2 oz semi-light, and “8” would be a heavy 8 oz switch.

The switches identified solely by a circled letter are models that were made obsolete during the series lifetime. The model number is deleted and replaced with a chart revision letter. On the engineering charts, the obsoleted models are listed, but it is not always clear which entry corresponds to which model, as multiple models could have been made obsolete in the same revision.

Clearer details of the switches will be forthcoming, pending completion of collection and analysis of charts.

A source of “↓” indicates that the switch is given in the keyboards table that follows the switches table.

Catalogue listing Action Output Plunger colour Plunger style Source NSN
1SW1-R Parts listings
1SW11 Momentary Black Sloped 5930-00-524-0338
1SW11-R Black, green Sloped eBay (date 7409), 1SW Chart 1 5930-00-524-0338
1SW11-R1.5 Green Sloped 1SW Chart 1
1SW12-BL Black Stepped Deskthority
1SW12-R Green Stepped 1SW Chart 1, eBay (date 7703) 5930-01-141-2002
1SW13-R Alternate Black Sloped 1SW Chart 1, eBay (date 8121) 5930-01-039-3169
1SW14 NSN 5930-01-174-7525
1SW14-R
1SW15-R Momentary Black Sloped 1SW Chart 1
1SW17 Momentary Black Sloped 5930-01-046-3393
1SW17-R Momentary Blue Sloped 1SW Chart 1 5930-01-046-3393
1SW17-R1.5 Momentary Blue Sloped 1SW Chart 1
Momentary Blue Sloped 1SW Chart 1
Momentary Blue Sloped 1SW Chart 1
Momentary Blue Stepped 1SW Chart 1
1SW17-R2 ? Blue Sloped? eBay (date 9541)
1SW17-R8 ? Blue Sloped? eBay (date 8444)
1SW18 NSN 5930-01-337-6279
1SW18-R ? Black/Blue Stepped eBay 5930-01-155-5558
1SW19-R Momentary Blue Sloped 1SW Chart 1
Momentary Black Stepped 1SW Chart 1
1SW21-R Momentary Black Sloped 1SW Chart 1
1SW23-R Parts listings
1SW31-R Momentary Green Sloped 1SW Chart 1
1SW41-R Momentary Green Sloped 1SW Chart 1
1SW43-R Momentary Red Sloped 1SW Chart 1
1SW45-R Momentary Green Sloped 1SW Chart 1
1SW51 Momentary Sink level Black, red NSN 5930-01-046-0767
1SW51-R Sloped 1SW Chart 1, eBay (date 8446), eBay (9511) 5930-01-036-5181
1SW51-R1.5 Sloped 1SW Chart 1
1SW52 NSN 5930-01-337-6280
1SW52-R Stepped eBay (date 8742)
1SW52-R8 Stepped 1SW Chart 1
1SW53-R Alternate Black Sloped 1SW Chart 1 5930-01-175-8352
1SW54-R Alternate Black Stepped 1SW Chart 1
1SW55-R R&J Components Corp
1SW71 Black Sloped stemless eBay (date 9412)
1SW101-R NSN 5930-01-039-3167
1SW107-R NSN 5930-01-039-3168
1SW111-R Parts listings
1SW121 NSN 5930-01-354-7030
1SW121-R NSN 5930-01-354-7030
1SW151-R Parts listings
1SW152-R NSN 5930-01-039-3170
1SW181-R Illuminated White Sloped eBay
1SW201-R Parts listings
1SW204-R Parts listings
1SW300-R Momentary Black Stepped 1SW Chart 1
1SW301-R Momentary Black Sloped 1SW Chart 1

Keyboards

Schema

The model number schema for SW Series keyboards is as follows:

KSWA-B

K
Number of keys (at least two, as “1” in this position denotes a single switch)
“SW”
Series name
A
Unknown
B
Unknown

Subseries

There are at least two known subseries:

12SW Series
Current sinking non-encoded 12-station keypads (can be paired as a 24-station assembly)
16SW Series
Current sinking non-encoded 16-station keypads (can be paired as a 32-station assembly)

Documented

For more details, see Documentation below.

Model Description Output Rollover Lock Keycaps Source
50SW11-50 Keypunch Keyboard System 3 Code NKRO Sloped Product Brochure SW (373)
51SW5-1 Key-to-Tape/Disc Keyboard EBCDIC 2KRO Sloped Product Brochure SW (373)
51SW12-1 Typewriter Keyboard 6-bit address code NKRO Secretary shift lock Sculptured Product Brochure SW (373)
53SW1-2 Teleprinter Keyboard US ASCII 2KRO Sloped Product Brochure SW (373)
61SW12-1 Communications Keyboard Full US ASCII NKRO Electronic with LED Sculptured Product Brochure SW (373)
63SW5-4 Teleprinter Keyboard Full US ASCII 2KRO Alternate action Sloped Product Brochure SW (373)
70SW12-1 Remote Batch Keyboard US ASCII NKRO ? Sculptured Product Brochure SW (373)
75SW12-2 Communications Keyboard US ASCII NKRO Alternate action Sculptured Product Brochure SW (373)

Discovered

The following is not a complete list of all known SW keyboards. It only lists keyboards where at least one switch model is shown, or where it is particularly early or late production. In almost all instances of SW keyboards found online, the switch part numbers are not all shown, or are not shown at all (except for where it seems the switches were not marked in the factory).

Keyboard Micro Switch model Switches Date code Reference
Bare assembly 64SW1-4 Not shown 7012 flickr.com
Decision Data 8010 54SW11-14 1SW17 (sink pulse), 1SW11 (source level) 74/34 flickr.com
Custom keyboard Unreadable 1SW17 (sink pulse), 1SW51, … ca. 1980 deskthority.net

Other components

Cat. listing Component
500SW90-3 Sealed keyboard plunger (eBay); these can be seen in a 26SW3-3-S keypad
500SW90-5 Uncertain (NSN 5930-01-368-9087), allegedly a pushbutton switch
SW-11485 Keycap puller; depicted in PK 8919 2 for use with SD Series

Documentation

Honeywell have kindly provided 1SW Chart 1, which is freely available to all. Additional charts will be posted at a later date, once they are suitably redacted.

Product Brochure SW “Solid State Keyboards” and Product Sheet 51SW12-1 “Typewriter Keyboard” are in item SILNMAHTL_31166 at the National Museum of American History Library (part of the Smithsonian Institution), who kindly provided scanned copies of both documents. The dates for these documents are derived from the three-digit codes placed at the bottom of the last page of each. Product Brochure SW—seemingly from March 1973—is mentioned on Electronic Design 17, page 118, from the 16th of August, 1973.

See also