Licon and Cortron (ITW)

Contents

• Overview
• Numbering
• Patents
• Switch types
  • Ferrite core
  • Capacitive leaf
  • Mechanical
• Series
  • Series 550
  • Super Switch
  • Series 555
    • Style A
    • Style B
  • Series 54
  • Series 56
  • CP-4550
  • Series III
  • SS3
  • Series FC-2550
  • Series FC2500
  • CP6500
• Keyboards
• Documentation

Overview

Cortron was created as a spin-off from Licon, as a dedicated keyboard manufacturer, as noted in the Series 555 advertisements in Computer Design magazine in September and December 1976 (see Documentation below). Cortron was later sold to Amkey, who went on to merge with Cortron, with the new company taking Cortron’s name.

Details about the new Amkey-owned Cortron and present-day Cortron can be found on the Amkey and Cortron page.

Numbering

This page is at present an overview of ITW Licon and ITW Cortron keyboards, prior to Amkey’s acquisition of Cortron. Details on the product families is fairly scarce still.

The general pattern of the part numbers seems to be as follows:

The specific breakdown between series is only a guess at this time, as there are just too few examples of anything except Series 555. In particular, no linear DIN-compliant ferrite core types have ever been found, and most DIN-compliant ferrite keyboards are not properly documented. No keyboards from before Series 555 have been documented; one example was listed on eBay with photos that did not clearly show the switches, but that listing is now long gone.

Note that the third and fourth digits of the PCB part number correspond to the first two digits of the keyboard part number.

Patents

The table below provides an overview of relevant Illinois Tool Works patents, taken out on behalf of Licon and Cortron for keyboards. Several patents (thus marked) all derive their priority from application US14490271A (filed in May 1971), themselves filed in 1972, 1974 and 1981, with one of the patents filed in 1974 not being granted until 1985.

“Series 555” is used to indicate switches found in Series 555 keyboards, until we know the series identity of “Style A”, as it may not be part of Series 54.

US patent 4453063 says of the keycap mount, “This sleeve is not illustrated since the key cap and the switch actuator are old.” Likewise, of the switch implementation, “Various details of structure of the switch are not shown since they are old and are of no consequence to the present invention.” As such, it appears that the DIN-compliant design (FC-2550 and/or FC2500) were not patented, with the means of reducing the size of the switch not deemed to fall outside of the existing patents.

Switch types

Ferrite core

These are solid state switches which are sensed by controlling whether or not current will pass inductively from one wire to another through a ferrite core. They have been referred to as “magnetic valve” switches within the keyboard enthusiast community, but in advertisements from Licon and ITW, they are described as “ferrite core”. Here, the magnet in the plunger saturates the ferrite core—suppressing the inductance—and when the plunger is depressed, the inductance is restored and the key will be detected. These solid state switches are around the same age as Micro Switch SW, which is a Hall effect solid state keyboard series.

Cortron noted of these keyboards, “The Ferrite Core style switches were sensitive to PCB layout, grounding, and most importantly stray EMI or ESD. The way the wires or leads went up thru the core acted like antenna receivers or emitters, depending on inputs.”

The following diagram depicts two of ITW’s implementations; the original version used individual wires passed through the cores, before they moved onto discrete assemblies soldered to a printed circuit board.

In most cases, the older switches are all Micro Switch mount. The DIN-compliant types use a German-style snap on mount, although compatibility with German switches is not confirmed. However, HP 264XX Data Terminal keyboards use switches that appear to be designed for compatibility with Cherry M6 switches:

• HP 2645A keyboard, example 1
• HP 2645A keyboard, example 2

The technical literature for the simplified keyboard from this HP series—from August 1976—gives only HP part numbers for the “LICON” switches used.

Ferrite core keyboards are normally linear. Keyboards made for the Trendata 4000 use a patented click feedback system, found in US patent 3882295 filed in October 1973. The patent is titled “Tactile feedback switch mechanism” but it does specifically generate both audible and tactile feedback. The tactile feedback was added to simulate the feel and sound of “mechanical” switches, to avoid operator error arising from a lack of feedback that a key actuated. John “Jack” Spindler, who was part of the team at some point, noted: “They were also made to feel and sound like a Selectric typewriter keys. They felt that secretary would find transition easier.” This would not be the only product line designed to approximate the feel of an IBM Selectric.

As noted by Jack Spindler, the switch had the advantages of having no contact bounce and low manufacturing costs (with no intricate metalwork and very few parts per switch). The Deskthority forum topic Scanning a cortron Diablo keyboard demonstrates some of the complexity dealing with scanning the matrix, likely due to the very weak signals inherent in the design.

The inductive sensing created for their keyboards was later adopted by Licon for additional purposes. The article Transducers based on switch designs (Electronics vol. 48 no. 7, 3rd April 1975, pp. 39–40) describes the adaptation of the inductive keyswitch sensing for automotive sensing, in particular speed detection for anti-skid control. Later that year, the article Ferrite pot has no contact wear (Electronics vol. 48 no. 21, 15th October 1975, p. 34) describes a further adaptation to provide a contactless potentiometer, also intended for the automotive industry.

Capacitive leaf

This is a capacitive keyboard that uses a leaf spring under each key instead of a foam pad with foil attached. The design is very similar to Digitran Golden Touch switches. The examples below have a series of patents on the label but the switch patents thereon are for ferrite core switches.

Mechanical

At least two switch designs were also patented with mechanical contacts. So far, no ITW mechanical keyboards have been discovered.

Series

It appears that keyboards and switches were assigned separate series. Switch series names were likely all two-digit numbers, while keyboard series used three and four digits. The mechanical switches may have had alphanumeric codes, with Cortron suggesting something like “E3” or “E4”.

Series 550

Series 550 is presently the oldest known keyboard series. These keyboards, introduced around 1969, used threaded-wire switches. The oldest description of this series is from October 1969, and the patent for the encoding technique was filed in November that year. The oldest (and only) known depiction of the original switches is from an advertisement in Modern Data in December 1970. The rated lifetime was 25 million cycles. These switches do not use a PCB. Instead, a ferrite core is fitted to each switch, and one or more windings are fed through the cores, one per output bit. Unlike later designs, which only ever used a single wire for each winding, these switches were illustrated as using multiple wires for the windings.

Licon advertised a wired inductive encoding system where the encoding was defined by which sense wires passed through each ferrite core. This principle is covered under US patent 3638221 “Solid-state keyboard” filed in November 1969. The general principle is illustrated in the diagram below. The diagram does not cover the saturation of the induction cores; only the encoding technique is depicted. The advertisement in Modern Data shows many wires passing through the core, in accordance with the written description of the encoding used. The ferrite core wiring was automated in the factory.

In a letter to the editor, published in Electronics magazine on the 1st of March 1971 (page 8), John Pfeiffer from Licon offered a correction to a claim made in the In key with computers panel of the article Capacitive keys, simpler circuits add up to reliable keyboard from the 7th of December 1970 issue, where Licon’s keyboards were said to use TTL encoding. Licon countered:

… the Licon keyboard technology was misrepresented. One of its most important features is encoding at the switch, which allows the customer to choose standard or custom encoding formats without special tooling and eliminates the need for a diode matrix or MOS chip.

Within a year or so, the switch size was drastically reduced, as shown in a fresh patent. Keyboard 55-000084, manufactured for Sanders Data Systems, uses wired inductive low-profile switches exactly as per US patent 3714611 “Solid state switch construction”, indicating that the low-profile keyboards remained Series 550, although this is not verified by any literature. A 1971 advertisement in Electronic Design describes them, but does not name the series as the previous advertisement did.

Super Switch

Licon’s advertisement in Electronic Engineers Master 1973–74 Section 2000 is for an ASR33 keyboard with “Super Switch” ferrite core switches. From the top of the mounting plate to the bottom of the PCB, the height is shown to be 0.66″; this is effectively the distance for a Series 555 keyboard, suggesting that “Super Switch” could denote a switch series used in Series 555 keyboards.

However, a Super Switch keyboard was previously advertised in the Electronic Engineer in December 1972, with a switch design that does not match any patent or known switch type. Only the top of the switch can be seen (not including the plunger), making indentification difficult. These switches are also soldered to the PCB.

Keyboard 55-100007 from 1971 was most likely a Super Switch keyboard, with the implication that Super Switch keyboards were Series 551. The switches appear to be visually identical from above to the low-profile Series 550 switches, while the “Style A” switches used with Series 555 are a little different: the notches used to access the plate retention prongs are covered over in Series 555 keyboards, and the switches are a different design below the plate.

Series 555

Series 555 keyboards use low-profile ferrite core switches. These switches are specifically designed to be soldered to the PCB, although this change appears to pre-date Series 555. Patents for switches used in Series 555 date back to 1973, and the oldest advertisement discovered to date for Series 555 is from Computerworld, December 1972. A later Series 555 advertisement from Computer Design in September 1976 shows that both of the switch styles depicted in US patent 3902032 “Magnetic key switch having a removable support assembly” are used in the same keyboard series.

Although these keyboards are covered by a number of patents, most of these keyboards are marked as being covered by US patent 3035253, filed by George C Devol on magnetic storage.

This series includes a double-action switch that uses two ferrite cores. These switches are much taller than the standard momentary types, and while one could be forgiven for thinking that they belong to Series 550, they were patented after the standard Series 555 switches. These double-action switches can be found alongside standard-height momentary switches in the HP 9845 workstation keyboard.

Series 555 secretarial shift can be seen in the Xerox X998 keyboard.

Style A

This style of switch is rare. This design is so far only known from a Univac Uniscope 100 keyboard and for some of the alternate action switches in HP’s 9845B/C keyboard and 2645 keyboard. Style A switches keep the shell and the ferrite core assembly separate: removing the shell leaves the ferrite core assembly behind on the PCB. The design of the switch above the mounting plate is only marginally altered from previous switch designs.

The 1976 and 1981 service manuals for the HP 2645 give us (via NSN information) Cortron part numbers 54-0013 and 54-0202, suggesting that “Style A” switches are indeed part of Series 54, although stronger confirmation is still required.

Style B

This is the standard form of switch used in Series 555 keyboards, which is widely encountered, with examples ranging from the mid-1970s to the mid-1980s. These switches appear to be Series 54 Superswitch II; it is not known whether Style A also falls under Series 54. These switches have the ferrite core assembly snapped tightly into the switch shell.

Series 54

Series 54 “solid-state” keyswitches got a brief mention in Computerworld, 31st of May 1976. This series was further mentioned in the NCC 1976 booth announcement for Licon, which refers to “series 54 Superswitch II standard, tactile, alternate action, double depression, incandescent, and LED keyswitches.” These switches are not depicted. It’s curious that the term “SS3” is later used for Series III switches; possibly those are “Superswitch 3” not “solid state 3”.

Indications are that these switches are the “Style B” type in the Series 555 keyboards. The paper The Licon Wheel Velocity Sensor—An Application of Ferrite Core Technology (Edward F Sidor and Rand J Eikelberger, Licon, 1976) appears to depict such a switch and makes reference to Licon Product Bulletin No. 05503 “Series 54 Superswitch II Keyswitch”, ITW Licon Application Note No. 05504 “Series "54" Keyboard Switch” and ITW Licon Technical Memorandum No. 230. “Technical Data, S.S. II, 0.180 Inch Travel, Single Sense, Non latching.”

A number of ITW parts beginning with “54-” are known. Some relate to keyboard switches, and some were located only via NSN information:

Series 56

Series 56 appears to be the keycaps that went with Licon Series 550 keyboards, based on a leaflet included with sample parts that may date to 1976. These are double-shot moulded keycaps, with the material given as “SAN copolymer”, denoting styrene-acrylonitrile resin. The slot in the keycap that accepts the plunger is shown to be 0.030±002″ wide and 0.250±0.002″ front-to-back, with a vertical depth of 0.340″ minimum. The keycaps are 0.716″ square and 0.477″ tall.

It would appear that Licon offered these keycaps for sale separately.

CP-4550

CP-4550 is a metal leaf capacitive system. The original design is covered by US patent 4352144 “Capacitive keyswitch with overtravel plunger mechanism”, filed in January 1981. The switch as illustrated in advertisements in Computer Design magazine in April and May 1981 exhibits a notable difference from the patent: the capacitive leaf has a tongue portion for the plunger to engage. This is effectively the same design as Digitran’s Golden Touch capacitive keyboards, that Cortron appear to have copied.

Cortron CP-4550 is mentioned briefly in Interface Age, August 1981 on pages 132 and 134, and is said to use the “CP-4550 keyswitch”. This switch is said to give an “exceptional, true linear feel” and is “environmentally superior to foam pad design approaches”. The rated lifetime is in excess of 100 million cycles.

The Recent Microsystems Announcements from Computer magazine, June 1981 cites this model as being a “Solid-state, capacitance unit”, with a unit price of $45 in volume quantity ($127 in June 2019). The $45 price also appears in the Computer Design magazine advertisements.

As with many other capacitive designs, CP-4550 keyboards have an external return spring visible under the keycap. This spring is however held captive by the plunger and will not be misplaced after removing a keycap. As with Series 555, the keycap mount appears to be Micro Switch.

All CP-4550 keyboards observed to date appear to have Comptec SA family keycaps.

Series III

Series III was advertised in Computer Design in July 1978 (and in later issues), with further details given in a written advertisement in August. Series III keyboards use SS3 ferrite core switches. The patent for the SS3 switches was not filed for nearly a year afterwards.

The only identifying marks of these keyboards is that the internal part numbers take the form 35-5xxxxx. As with Series 555 keyboards, these keyboards are also marked with US patent 3035253.

SS3

SS3 is a ferrite core keyswitch. “SS3” is likely to denote “Superswitch III”, that is, the third generation of self-contained ferrite core keyswitch. The design of the SS3 switch is not depicted in any known Cortron advertisements; instead, it can be seen in Celanese advertisements for two of the resins used for the switches: Celanex 2012 polyester resin for the base, and Celcon acetal copolymer resin for what appears to be the top cover.

The full-page Series III advertisements describe SS3 as follows:

Like its proven and successful predecessor, the SS3 keyswitch is mechanically simple and contactless. The SS3 is designed with fewer parts, lower profile and exceptional feel while maintaining excellent resistance to environmental factors. This combined with a 100 million cycle life test rating offers unsurpassed cost efficiency.

The shorter Series III advertisement notes:

ss3 keyswitches are contactless, with a low profile–0.5″ (1.27 cm) from mounting plate to keyboard bottom. Switch travel is a full 0.150″ (3.81 cm). Life test rating is 100M cycles.

Compared to the earlier Series 54, the keystem on the plunger seems to sit a fraction of a millimetre higher: SS3 does not seem to offer a keyboard that is overall any smaller that its predecessor. The distance from the PCB to the top of the mounting plate is however reduced by around 4.1 mm, from around 14.35 to 10.25 mm, and the plunger shaft appears to be specially reduced to allow the keycap to move down over it. The distance from the bottom of the mounting plate to the bottom of the terminals would be around 12.5 mm, which is the only measurement that would fit the advertised description. The term “keyboard bottom” may refer to an unenclosed keyboard module; it certainly could not describe an enclosed keyboard with the switches in question. Indeed, SS3 does seem a little tall considering the era, and seemingly unnecessarily so.

The claim of “fewer parts” is also a stretch. The Series 54 housing was a single piece, but the ferrite core assembly used a two-part snap-together enclosure. SS3 does away with the separate enclosure, but instead requires a cover to secure the ferrite core and windings, thus saving all of one part per switch. It’s not clear what precisely SS3 offers over Series 54. True low profile would follow in a few years in the form of the FC-2550/FC2500 DIN-compliant keyboards.

The earliest known advertisement for Series III is from July 1978. The patent for the switches, US patent 4227163 “Electrical keyswitch”—was not filed until March 1979. The Celanese advertisement depicting the switches would not appear until a year after the keyboards were advertised, in August 1979.

Options for SS3 switches include upright versus angled keystems, center illumination, dummy switches for wide key stabilisation, and multiple key weights.

The patent also covers a mechanical switch type that appears to share the same housing as the ferrite core type. Thus far, there has been no sign of the mechanical type.

Series FC-2550

Series FC-2550 is a DIN-compliant ferrite core design, advertised in 1981. These too are advertised with a 100 million cycle lifetime. FC-2550 switches are stated to have “true linear feel”.

Series FC2500

In Computerworld, 28th March 1983, Illinois Tool Works advertised Series FC2500 keyboards. These are described as “low-profile” and offered linear and tactile options. In Computerworld, 2nd July 1984 it is also noted that these keyboards were reported to meet a 30 mm height requirement. Series FC2500 is a candidate for the low-profile type that was later manufactured by Devlin in the UK, as currently there are no indications of FC-2550 being tactile. In neither case were any illustrations provided. An illustration of a switch is shown in Computer Design in May 1983 (see Documentation below), which is a good match for the 25-50xxxx keyboards.

The article La Tastiera in the Italian magazine Selezione di elettronica e microcomputer from June 1985 contains the following description of Series FC2500 on page 59:

Tastiera ITW Cortron con feedback sia tattile che visivo. Il modello FC2500 emette un suono simile a quello di un grillo quando viene premuto un tasto. Essa adotta la tecnologia a ferrite; il feedback tattile è fornito da interruttori a cupola.

This translates to:

ITW Cortron keyboard with both tactile and visual feedback. The FC2500 model emits a sound similar to a cricket when a key is pressed. It adopts ferrite technology; tactile feedback is provided by dome switches.

Computer Weekly (supplement) 5th of January 1984 announced the launch of an unspecified series of Cortron ferrite core keyboards, noting:

The low profile keyswitch measures 17.1 mm high with keytop, 21.9 mm, and has a full travel of 4mm. Keyswitches can be provided with linear or tactile feel.

It seems strange that FC-2550 was seemingly advertised before FC2500. Because so few ITW DIN-compliant keyboards have been properly documented, there is no way at present to determine whether FC2500 and FC-2550 use different part number prefixes.

CP6500

“CP6500” is mentioned briefly in an article in Electronic Design magazine from 1985 (Alphanumeric keyboards, Mike Mullin, Electronic Design 33, 21st November 1985):

Plate-capacitive keyboards are very similar to the pad-capacitive types, except that a movable plate is mounted directly to the key top, with no pad in between. When the key is pressed, the plate approaches but does not touch the fixed plate. This switching arrangement is used by Illinois Tool Works Inc.’s ITW Cortron Division (Elmhurst, Ill.) in its CP4500 and CP6500 conventional and ergonomically designed keyboards.

One might assume that “CP4500” is the same as CP-4550, but this is not proven. CP6500 has yet to be discovered.

Keyboards

The following is a list of known Licon and Cortron keyboard models with both the switch type and part numbers known, arranged in date order:

The serial numbers appear to be monotonic, but on at least two occasions ITW seem to have started a new numbering range. The Taiwan-made example has a serial number from a separate system.

Note that the controller chips on newer keyboards all appear to have part numbers in the range 80-552xxx, regardless of keyboard series. Series 555 keyboards have controller or encoder chips with part numbers in the same 80-551xxx range as the keyboard PCBs.

Two models, 55-500161 and 55-500135, use a Deltrol Controls 100C Series clapper solenoid as a clicker. The underlying device is a conventional solenoid, but Deltrol only have “Core Tron” listed as a customer of this long obsolete part, and it may have been custom ordered with a modification that makes it operate solely as a clicker.

Documentation

The material below was scanned by Bitsavers unless otherwise noted.

• Licon Series 550 advertisement, Electronic Design, Vol. 17 No. 22, October 25 1969
• Licon Series 550 Keyboard advertisement, Electronic Design, Vol. 17 No. 23, November 8 1969, pp. 46–47
• Licon Series 550 keyboards advertisement, Modern Data, December 1970, page 8
• Licon fail-safe N-key rollover advertisement, Electronic Design, Vol. 19 No. 9, April 29 1971, p. C37
• Licon Series 550 advertisement, Electronic Engineers Master 1971–72 Volume 1
• Licon Series 550 keyboards advertisement, The Electronic Engineer, Vol. 30 No. 9, September 1971
• Licon low-profile keyboard advertisement, Electronic Design, November 25 1971, page 101
• Licon N-key rollover keyboards advertisement, The Electronic Engineer, Vol. 30 No. 12, December 1971
• Licon Super Switch Keyboard advertisement, The Electronic Engineer, Vol. 31 No. 12, December 1972
• Licon Series 555 keyboard advertisement, Computerworld, Vol. 6 No. 52/Vol. 7 No. 1, December 27 1972/January 3 1973 (unclear origin; from the Internet Archive)
• Licon ASR-33 solid state keyboard advertisement, Electronic Engineers Master 1973–74 Volume 1
• Licon booth announcement for NCC 1976 including a mention of series 54 Superswitch II, Computer Design, Vol. 15 No. 5, May 1976, page 141
• Cortron advertisement, Computer Design, September 1976, page 5: covers the spin-off from ITW, and depicts Series 555 (cleaner scan from November)
• Cortron Series III Solid State Keyboards advertisement, Computer Design, July 1978
• Cortron Series III advertisement, Computer Design, August 1978
• Celanese Celanex 2012 and Celcon advertisement (featuring ITW Cortron SS3), Plastics Design and Processing, Vol. 19 No. 11, October/November 1979 (obtained via the Internet Archive, and converted to PDF)
• Cortron CP-4550 advertisement, Computer Design, April 1981, page 115
• Cortron FC-2550 advertisement, Computer Design, May 1981, page 155
• Cortron FC2500 advertisement, Computer Design, May 1983, page 76