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MEI T-5 Series

Contents

Overview

T-5 is a series of mechanical keyboard switches from Mechanical Enterprises. Unlike most MEI keyboard switch series, T-5 appears not to have been patented, so there is no suggested date of introduction. It was available by 1977, and remains in production to this day from Datalux (the successor to MEI), although very few types are still available.

T-5 switches are comparatively tall; the shell height is 18.2 mm including the stand-offs, which is fractionally shorter than Cherry M6.

Specifications

Operating force Momentary single pole:
3.5±0.5 oz (99±14 gf) (EEM 1985, 1988, 1989)
3.0±0.5 oz (85±14 gf) (catalogue, date unknown)
Alternate action, double pole:
6.0±0.5 oz (170±14 gf) (EEM 1985, 1988, 1989)
5.0±0.5 oz (142±14 gf) (catalogue, date unknown)
Contact bounce 4 ms maximum
Initial contact resistance 100 Ω maximum
Pretravel 0.080±0.030″ (2.0±0.76 mm)
Full travel 0.170±0.010″ (4.3±0.25 mm)
Rated lifetime For 5 V at 100 µA:
10 million (EEM 1985, 1988, 1989)
20 million (catalogue, date unknown)

Part number schema

According to the catalogue excerpt, the part number schema is as follows:

T-5S-A-CC(-HS)

“T-5”
T-5 series (also written as “T5”)
S
Sub-series (e.g. C, D, H, J etc; see table below for known subseries)
A
Action: M = momentary; A = alternate
CC
Contact arrangement: NO = SPST NO, OO = DPST NO, OC = SPST NO + SPST NC
“HS”
The exact meaning is not given, but it can be treated as denoting “heavy spring” as this suffix indicates the use of a 5 oz return spring (single pole momentary action types only)

Subseries

T-5 series is divided up into subseries based on design. Each catalogue or advertisement discovered to date contains details of a small portion of the series, listing only a small number of the different subseries. Some subseries are known only from NSN records. The subseries found to date are listed below. The general descriptions below are unofficial, while the descriptions marked “1982” come from the 1982 advertisement in Electronic Design magazine.

Sub-series General description Official description
T-5B Takes low-profile keycaps, possibly short keystem; sloped profile Plain ¾″ flat truncated (1982)
T-5C Standard momentary type, sloped profile Plain ¾″ flat truncated (1982)
T-5D Undocumented; unsprung stemless plunger, with two spring-loaded possibly gold-plated pins protruding from the top
T-5H Shown in the 1988 and 1989 advertisements in outline form; some kind of stemless design
T-5J Sealed illuminated, with inside-fit box lens keycap ¾″ sealed and lighted (1982)
T-5K Illuminated, with inside-fit box lens keycap ⅝″ lighted (1982)
T-5L Illuminated, with outside-fit box lens keycap ¾″ lighted (box lens) (1982)
T-5P Stemless
T-5Q Sealed, with low-profile keycap Sealed flat truncated (1982)
T-5S Standard momentary type, stepped profile Plain ¾″ stepped truncated (1982)
T-5V Unknown illuminated (absent from catalogue excerpt)
T-5Y 2-unit version of T-5L, with strut-stabilised box lens keycap

The illuminated type sold by STRONIC does not match any of these drawings sufficiently, and appears to be another variant still. (It appears to be a modification of T-5L.)

Subseries T-5V (written in the alternative form as T5-V) is taken from the description of a set of keycaps made by Honeywell (CAGE code 27914) all described as “Fits with mechanical enterprises T5-V key switch”. NSN 7025-01-461-8550 is described as “Special Features: Lighted keytop with blue skirt and white”, while other items in this series (48 NSNs, including 5930-01-421-4908 to -17, -20 to -28 and -31 to -48) are all described as “Special Features: Blue skirt with white top, fits mechanical enterprises key switch T5-V”).

Subseries T-5L can be used with either a box lens (cuboid keycap) or a truncated lens (standard-shaped keycap). In 1982 it was advertised only with a box lens, but in 1985 it was advertised as being available in either configuration, just as it was in the catalogue.

The descriptions of T-5B and T-5C are the same, but T-5B is depicted with a considerably shorter keycap, somewhere around half the height of the full-size keycaps. This would suggest that T-5B has a shorter keystem.

Variations

The series has a number of unexplained variations. Most prominent is the use of the term “WEAB”, which can occur on any of the top, bottom or plunger. Some switches are branded only “MEI”, some are branded both “MEI” and “WEAB”, and some are branded solely “WEAB”. The term “WEAB” has so far not been found to correspond to any particular characteristic, be that terminal plating/tinning, plunger pigmentation or keystem. Datalux themselves do not recognise the term, nor do former importers Devlin.

Plungers can be either black or dark grey; the dark grey pigmentation appears to be metallic based on the swirls and the way it reflects light, but it is non-conductive (thus seemingly not related to electrostatic discharge protection). The grey colour does not directly correspond to any other characteristic, be that keystem, weight or “WEAB” marking.

Datalux confirmed that current production models use gold-plated terminals; the contact wire is also gold-plated. However, some variants instead have only one gold-plated terminal, specifically the terminal used as the stationary contact. In these variants, the other terminal has a grey finish that is too dark and dull to be silver plating (as used in some Cherry M9 variants); it is possible that instead the terminal is tinned. The grey colour continues all the way inside, where it is distinctly matt finish. Having both terminals gold plated does prevent oxide build-up between the contact wire and its terminal.

A red plunger stemless switch also exists. The terminal plating colours suggest T-5 (photos from Deepak Kandepet):

View full-size image View full-size image View full-size image View full-size image

This example is assumed to be a T-5P variant.

Parts

Very view part details have been discovered. A number of discovered types presently have no known part number.

Confirmed parts

The following table shows all recovered part numbers, either from their NATO Stock Numbers or from the catalogue excerpt retained by RS that was annotated with their own part numbers. Thus far, no service manuals have been obtained with part numbers in.

Part NSN RS
T-5C-M-NO 5930-01-158-2430 337-217
T-5C-A-NO 5930-01-252-6112 336-208
T-5C-M-NO-HS 335-794
T-5D-M-OO
T-5D-M-OO-W 5930-01-413-3432
T-5K-M-NO 5930-01-156-5708
T-5K-M-NO 5930-01-240-5290
T-5K-M-NO-HS 5930-01-326-9847
T-5K-A-OC 5930-01-253-8570
T-5L-M-NO 5930-01-056-3613 336-191
T-5L-A-NO 5930-01-056-3613 336-185
T-5L-A-OO 5930-01-056-5151

Available parts

As of March 2019, the following types are still available; for a small one-off order, they are $10.50 each, and $4.95 each for an unspecified larger quantity.

Alternate action and DPST NO+NC are no longer produced. Heavy spring (-HS) versions may still be available.

Observed variants

The following table lists directly observed examples (rather than catalogue listings), and their specific characteristics.

Variant Part Branding Plunger colour Terminal colours Keystem Known from
Top Base Plunger
Momentary non-illuminated T-5C-M-NO MEI Black Gold Standard tall Sold by RS via Devlin and by Datalux
Momentary non-illuminated heavy T-5C-M-NO-HS Sold by RS via Devlin
Momentary non-illuminated ? MEI MEI WEAB Dark grey Gold and silver Standard tall UK101; unknown keypad
Momentary non-illuminated ? WEAB ? WEAB Dark grey ? Standard tall Digicomp DR-70
Momentary illuminated T-5K-M-NO MEI Black Gold Inside-fit illuminated Sold by Datalux
Momentary illuminated T-5L-M-NO MEI Black Gold Outside-fit illuminated Sold by Datalux
Momentary illuminated ? WEAB Dark grey Gold and silver Outside fit Sold by STRONIC
Momentary illuminated T-5L-M-NO ? MEI Dark grey Gold Outside fit BargainMarge
Momentary non-illuminated ? WEAB WEAB Dark grey Gold Custom Scanvægt 810422
Momentary non-illuminated ? WEAB MEI Black Gold Short angled Volker Craig
Alternate action non-illuminated ? Gold and silver
Unknown T-5C-D-OO MEI Black Gold Unsprung stemless Sold by Datalux

Occurrences

See also

Documentation