- Example keyboards
The Maxi-Switch Company (later Maxi Switch Inc) was an American switch and keyboard manufacturer. Barely any literature has survived, but a few details have been recovered. Maxi-Switch are also known for manufacturing a subset of IBM Model M keyboards in Mexico.
One has to wonder if the name “Maxi-Switch” was a play on Micro Switch.
Maxi-Switch was founded in 1968 in Minneapolis. The owner sold the business to EECO (Electronic Engineering Company of California) in 1984. Maxi-Switch had a keyboard plant in Carborca, Mexico and a keyboard and switch business in Scotland, as well as a keypad manufacturing plant in Phoenix, Arizona. In May 1990, EECO filed for bankruptcy protection, and in July that year, the keyboard division was sold to Silitek of Taiwan. Silitek announced they would retain the Tucson, Arizona facility and rename it Maxi Switch Inc.
In December 1995, Maxi Switch “agreed to acquire the manufacturing rights, patents and assets for Lexmark International Inc.’s Select-Ease and Rubber Dome computer keyboards, including a patent for its Buckling Spring technology.”
The only documented correspondence between a series name and PCB code is for the 2900 Series hexadecimal keyboard from 1977, whose PCB is marked 2903-014-02 and whose part number is 2129-011. Other keyboards with block reed switches have PCB codes that begin “29” and part numbers that begin “2129”, suggesting that the PCB code indicates the series name, and that the first two digits of the series name are the third and fourth digits of the part number.
An unidentified keyboard with some form of discrete switch has a PCB code 3101-090-02 and part number 2132-033. As Series 3100 is documented a mechanical switch type, this would seem to strengthen that PCB code theory. The fact that the part number begins “2132” instead of “2131” cannot be explained.
The rubber dome keyboards however are more confusing. Here, the part numbers typically begin “2186” (PCB) or “2189” (membrane) or “219”. This would suggest series 8600, 8900, 9100, 9200 etc, but it may be that they simply stopped using series names at this point.
Some series are confirmed from the 1973 Electronic Engineers Master advertisement; see Documentation below.
The following series names are confirmed from literature.
Series 1600 and 1800
These are keystrip modules that can use reed capsules (28 V DC at 250 mA), cross-bar palladium contacts (3 A at 28 V DC or 115 V AC) and snap-action power contacts (only in Series 1600, 15 A at 250 V AC or 500 mA at 125 V DC). Series 1600 is 1.5″ high and Series 1800 is 1.1″ high. Key spacing can be 0.625″ or 0.75″.
Series 2700 was advertised as “pre-tested” reed switches; they are comparatively tall, cylindrical switches with fins that appear to attach the switch to a mounting plate. Series 2700 was described as “new” in Electronic Engineers Master catalogue in 1973 but it was also advertised in Electronics in September 1972. Bounce time is 0.4 ms maximum, with 200 mΩ maximum resistance and a current carrying capacity of 500 mA in DC-resistive applications. See Documentation below.
2900 Series comprises ganged reed blocks, with a reported lifetime of over 100 million operations and a 2.5 oz (around 70 g) operating force. The reed capsules can be individually replaced in the field through holes in the PCB. The plastic blocks house only the plungers, not the switch mechanism, which is soldered separately. This is the only confirmed series to date to be examined.
The reed blocks have a base to contain the return springs, and are secured to the PCB with screws and nuts. It appears that two nuts are placed onto each screw: one to hold the switch assembly together, and one to secure the assembly to the PCB.
2900 Series seems to be largely identical to a type of Key Tronic reed switch, leading to the question of who had the design first. The Key Tronic design can be seen in a 1978 Sundstrand keyboard. The leaflet with the 2900 Series hexadecimal keypad appears to be dated April 1977.
2900 Series was advertised in Computer Design magazine in November 1977, with a cutaway illustration of the switch; see Documentation below.
Series 3100 is a mechanical switch type. It is described as having wiping contacts. In Electronic Design Vol. 21 No. 17 from 16th of August 1973, Series 3100 was stated as having “dual bifurcated gold contacts” and a lifetime of 10⁶ (one million) operations under load. Series 3100 encoded keyboards were said to cost as low as $50. The same advertisement was repeated over a year later Electronic Design Vol. 22 No. 26 from the 20th of December 1974 (page 124, PDF page 143), with a single modification: the rated lifetime for Series 3100 was increased to 10⁷ (ten million) cycles.
The unidentified keyboard 3101-090-02 listed below has switches marked “PAT.NO.” and a patent number ending “10,060”. The only US patent for a pushbutton switch from that era that ends with those digits is US 3710060A, filed in July by Bunker Ramo, and granted in January 1973. The patent is contemporary with the Maxi-Switch advertisement and the design fits: it has the side holes as seen in the photos and the dual bifurcated contacts (not for redundancy, but because it is double-break, or bridge contact) and the contact design appears to provide wiping motion. At no point was the patent ever assigned to either Maxi-Switch or EECO, however.
The Bunker Ramo design has additional contacts that press against the PCB to make its electrical connections, and is secured with a nut and screw. Maxi-Switch’s version has standard solder terminals. Deepak Kandepet collected another variant of this switch—entirely devoid of markings—from a Rockola jukebox panel. This type also uses solder connections to the PCB. This variant could be an original Bunker Ramo switch. Yet, unlike the Maxi-Switch type, it lacks the holes in the side of the case for the plunger, making it further from the patent than the Maxi-Switch type.
CAP-TRON is a block foam pad capacitive series. The design is very similar to Series 2900. The modules lack the base found in Series 2900 and are open at the bottom so that the foam pad can reach the PCB; consequently the return spring is placed under the keycap instead. The sense pads on the PCB are curiously not protected by solder mask.
CAP-TRON keyboards offered 2-key rollover or N-key rollover, with the switch having a rated lifetime of 100 million cycles. The change in capacitance is given as being seven times higher than required by the electronics, ensuring reliable operation.
The switches were advertised as “CAP-TRON” (see Documentation below), while in Electronic Design magazine in 1976 [ED1976-FOK] they are given as “Captron” without the hyphen. The one known PCB code suggests Series 4000. The only known example is the Digital Group KEY-1 keyboard.
6000 series was advertised in Computer Design magazine in April 1979. The keyboard advertised was microprocessor-driven with mechanical switches. The advertisement notes, “Electronic hysteresis eliminates switch tease and multiple char output problems.” There is a photograph showing a keyboard, but there is no way to determine what switch type is used.
The scope of 6000 series is unclear. The MAX-II (or MAX-11) keyboard (see Documentation) is documented as being 6000 series, giving us the specifications for the switches. David Given’s Maxi-Switch 2160029 appears to be a MAX-II, and it has “Maxi-Switch vintage linear” switches, as do all other Maxi-Switch keyboards with part numbers in that range. The original MAX advertisement shows the same PCB holes (for unpopulated key stations) as David’s apparent MAX-II, suggesting that the original MAX keyboard was also “vintage linear”. However, the advertisment also notes that the switches have wiping action, which is not a known behaviour of that type of switch.
For 6000 series, the specifications are as follows (taken from the Standard-Tastatur MAX-II product leaflet, given under Documentation):
|Total travel||0.120±0.017″ (3±0.4 mm)|
|Pretravel||0.050″ (1.27 mm)|
|Overtravel||0.070″ (1.77 mm)|
|Operating force||3.5±1 oz (100±30 gf) standard|
|Bounce time||Below 3 ms|
|Contact rating||12 V DC, 100 mA|
|Initial contact resistance||Below 1 Ω|
|Operating lifetime||10 million cycles|
The similarity of the switches to those of SMK JM-0400 series—including an identical alternate action design—strongly implies that SMK were involved, either by licensing their tooling, or by producing the switches for Maxi-Switch just as they did for NEC.
The bounce time, rated lifetime and electrical rating match the specifications of SMK JM-0400 mechanical switches when advertised in 1979. The seemingly later SMK J-M 9031 flyer gave the rated lifetime as 100 million cycles, and the operating force of 90±30 grams (90±20%) and pretravel (at exactly half way) of 0.06″ (1.5 mm) both differ from Maxi-Switch’s specifications.
These are identical in principle to Alps elastic contact, and are only known from the oldest TRS-80 Model 4 keyboards — see Maxi-Switch elastic contact illustration. The design of the shell bears a very strong resemblance to that of SMK KBS01 membrane switches, suggesting that they were also manufactured by or licensed from SMK.
Miniature elastic contact
These are a very low profile elastic contact type. The keycaps are retained by plastic frames that sit atop rubber domes. These frames are secured to the PCB using screws; at each key position there are two screw holes and two fixing pins in the frame. The frames are branded “Maxi-Switch Co” and come in sizes of one, three, four and five units.
In the HP 46086A keypad, each key has a single-unit frame and a single-unit dome. By comparison, there is also a Decision Data keyboard that uses all four of the known frame sizes and large rubber dome mats.
The leading digits of the PCB codes (87) do not correspond with the part numbers, which begin 2185 instead of 2187. A possible interpretation is a series name of 8000, but this is by no means certain. Note that the part number prefix of 2185 immediately precedes the prefix of the more common plunger-over-dome families with prefixes 2186 and 2189.
Clear distinction between rubber dome families is not yet possible. Tentatively it appears that part numbers beginning “2186” indicate conductive domes over a PCB, while part numbers beginning “2189” indicate conductive domes over a single membrane sheet. The PCB for HP 46086A (a keyboard with miniature integrated dome switches) has part number 2185074, which is very close.
As these keyboards are held to be of much less interest to anyone, disassembly photos are rare, which impedes understanding. This is muddied further by the acquisition by Silitek, as production was moved at least in part to Silitek’s factories, causing the adoption of Silitek’s own plunger-less switch design into the Maxi Switch range.
For now, they are being treated separately but collectively.
Mechanical, reed, capacitive, integrated dome
Note that some series names are hypothetical; see above for more details.
|Keyboard||PCB code||Part number||Date||Country||Serial|
|CAP-TRON||Block foam pad||Digital Group KEY-1 keyboard||403003-04||ca. 1976|
|2900||Block reed||Maxi Switch 2900 Series hexadecimal keyboard||2903-014-02||2129-011||ca. 1977||372-507|
|MCM/900 keyboard||293079||2129-069||ca. 1977||238 347|
|3100||Discrete mechanical||Unidentified keyboard||3101-090-02||2132-033||1111 456|
|6000||“Vintage linear”||Cybernetic Data Products keyboard||630010-09||2160029||USA||1488-440|
|Unidentified ASCII keyboard||630015-02||2160014||ca. 1979||436-090|
|Commodore PET add-on keyboard||630011-03||2160010||749-199|
|Billings 6000 keyboard||630067-03||2160148||1983-04-22||USA||1123|
|Kaypro II keyboard||630184-02||2160150||1983-07-29||USA||017098|
|Xerox 928-900451||630107-02||110S80577 2160132||1984-01-11||USA||016020|
|Geomet 200||KYBD 2160177||2160177||1984-07-24||1228|
|Maxi-Switch 2160029 (MAX-II or MAX-11?)||630010-11||2160029||1984-10-05||USA||016703|
|8700?||Miniature elastic contact||HP 46086A||870094-01||2185074||1981-08-06?||42570|
|Decision Data XT-layout keyboard||870069-04||2185041||1984-12-11||USA||022366|
|Keyboard||Part number or model||Type||Keycaps||Date||Country|
|Maxi-Switch ME 101||218603XXX||Conductive dome, plungers, PCB||Not depicted||Unreadable in photo||Unreadable in photo|
|Gateway 2000 AnyKey||2189014-00-211||Conductive dome, plungers, single membrane||Double-shot||1992-01-??||Mexico|
|Unidentified internals||2189XXX-XX||Conductive dome, plungers, single membrane||1995 week 23|
|Maxi Switch 2192004-XX-XXX||2192004-00-001||Silitek rubber dome over membrane||1993||Malaysia|
|ALR 2196003-XX-XXX||2196003-00-200||Standard plungers; other details unknown||Lasered||1997-11-15||Mexico|
- Maxi-Switch keystrips and keyboards advertisement, Electronic Engineers Master 1972–72 Volume 2 (scanned by Bitsavers)
- Maxi-Switch keystrips and keyboards advertisement, Electronic Engineers Master 1973–74 Volume 2 (scanned by Bitsavers)
- Maxi-Switch 2700 series advertisement, Electronics, September 11 1972 (scanned by or for WorldRadioHistory.Com)
- Maxi-Switch CAP-TRON advertisement, Computer Design, September 1976 (scanned by Bitsavers)
- Maxi-Switch 2900 Series advertisement, Computer Design, November 1977 (scanned by Bitsavers)
- Maxi-Switch MAX keyboard advertisement, BYTE, Vol. 3 No. 9, September 1978 (Internet Archive, unknown origin)
- Maxi-Switch MAX keyboard advertisement, Computer Design, September 1978 (scanned by Bitsavers)
- Maxi-Switch 6000 series advertisement, Computer Design, April 1979 (scanned by Bitsavers)
- Standard-Tastatur MAX-II product leaflet, scanned by David Given (the original was aready a poor quality photocopy)