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Digitran keyboards

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Overview

Digitran is a US company who formerly made computer keyboards for a number of years. Keyboard production has long since come to an end, and they report that no documentation remains on their keyboards. Digitran keyboards are fairly rare. They are best known for their “Golden Touch” metal leaf capacitive keyboards, although from the very few examples observed to date, this term is in only known to be associated with the second of their three known metal leaf capacitive types. The metal leaf capacitive system would later be seen in a keyboard from Cortron.

Model numbers seem to take the form of the series name (two letters) followed by a four-digit model code, typically followed by a one or two digit suffix code (except KL types). This is speculation based on the Series KL keypads, which are the only known instances of a series name.

All Digitran keyboard and keypads observed to-date are non-discrete designs; none of them contain separate switches.

Series

Series KL (Minikey)

Series KL comprises the “Minikey®” ultra-low-profile keypads, with snap-action leaf springs. This is the only series confirmed by name. The rest of the series names given below are derived from keyboard models in a manner analogous to Series KL, as they all share the same model number format.

KL keypads are covered by patent US 3800104 filed in 1972. Although these are short travel (pretravel is 0.05″ or around 1.27 mm, and full travel is 30% more, around 0.065″ or 1.65 mm), the general design may have been an inspiration for using metal leaves for capacitance.

These keypads are still depicted on the Digitran website in a montage photo, but are no longer mentioned. The Series KL Minikey datasheet is still present on their site however. The Wayback Machine shows that they were still in production as late as 2003, in the form of KL 2000 Series.

KS

This appears to be the oldest full-travel keyboard type discovered thus far. The only observed example is from 1976, but the single patent listed is US 3750113, filed in 1971. This patent only covers the controller circuit; a vague illustration of a single switch suggests a design closer to a normal foam pad approach.

Patent US 4090229 was filed in September 1976, one month exactly after the single known KS keyboard was manufactured. This patent details the switch mechanism itself, suggesting that KS-type keyboards date from late 1976.

KS keyboards are capacitive, and use a metal leaf as the movable capacitor plate. The Z shape of this metal leaf provides the overtravel. As the plunger presses on the centre prong, the thin sides Ⓐ flex first, bringing the capacitive area Ⓑ down above the corresponding pads on the PCB. The base Ⓒ of the central prong is much wider than the sides Ⓐ, and this makes the prong harder to bend. This allows Ⓑ to be pressed all the way down to the PCB without the plunger coming to stop immediately; the plunger continues to move, flexing the central prong in the process.

The plunger guide shafts are collectively formed from a single plastic moulding, making this an early keyboard to be produced in this manner; typical keyboards of this era would use a metal mounting plate with separate plunger assemblies that snap into that plate in the same manner as fully-discrete switches.

No photographs appear to exist of the underside of the keycaps; the mount itself is a strange design, and a photograph of the underside of a keycap is required to understand it.

KS99

InfoWorld, 16th of November 1981 (page 40) briefly advertises the KS99 keyboard, which is said to be their first standard, off-the-shelf keyboard model, with previous products being custom types for OEMs. It has N-key rollover. InfoWorld, 5th of April 1982 (page 16) goes into more detail, and states that it is capacitive.

KC

KC keypads adapted the capacitive arrangement to produce a conductive switch. Here there is no Z portion of the leaf spring. The centre of the leaf makes contact with a metal bar resembling a jumper, and the outer extent of the leaf appears to be able to flex downwards to provide overtravel. These are not marked with a patent. While they have standard keycaps, these switches have not been observed in a full keyboard, being observed only from keypads.

KM “Golden Touch”

Keyboards with “Golden Touch” written on the PCB have been found going back as far as 1983. These keyboards have model numbers that begin “KM” instead of “KS”. There seems to be little if any difference between the two types in terms of the switch mechanism. These keyboards are only known from Fortune Systems machines, and they do feature a metal mounting plate with discrete guide shaft modules for the plungers. Further, the types observed so far all appear to be Micro Switch mount, with thick plastic keycaps similar to Micro Switch’s. No-one else seems to have noticed this or checked.

KM keyboards also include patent US 4090229 on the label on the PCB, which is the patent associated with but not written on KS keyboards; they also list the capacitive circuit patent US 3750113.

KD (DIN compliant)

KD keyboards are a low-profile variant of capacitive leaf spring keyboard. There is no longer a mounting plate: the plunger modules attach directly to the PCB, with the guide shaft passing through the PCB. Retention clips secure the modules to the PCB from below. The keycap mount is a flat pad similar to the mount of later Oak Full-Travel Membrane keyboards.

The capacitance leaves are now on the bottom of the PCB, and are moved away from the PCB by a rod integrated into the plunger, making this an reversed arrangement similar to IBM beam spring, where lower capacitance indicates a keystroke. Two newer patents cover this revised design: US 4408252 (filed February 1982) for the switches, and US 4412754 (filed September 1982) for the space bar mechanism.

Examples

As noted, Digitran keyboards are rare, and only a few examples are known to date.

Model Description Date Switches Reference
KS0038-1 Harris Smart Terminal keyboard AUG 30 1976 Metal leaf capacitive Deskthority
KC0009-1 Keypad with standard keycaps APR 29 1981 Not observed eBay
KM0101-4 Fortune Systems KB12263; appears to be Honeywell mount FEB 15 1983 “Golden Touch” metal leaf capacitive Deskthority
KM0122-10 Fortune Systems 1001132-11 03/84 “Golden Touch” metal leaf capacitive Bitsavers
KD0158-01 Atex KD0158-01 10-84 Metal leaf capacitive, low-profile Deskthority
KM0130-02 Fortune Systems 1003474-01; appears to be Honeywell mount
(“KM” is a guess as there is no proper photograph of the label)
7-85 “Golden Touch” metal leaf capacitive Deskthority
KL0026 Keypad Not observed eBay
KL0199 Keypad 9318 Not observed eBay
KL0045 Keypad 9529 Not observed Instructables
KC0246-01 PCB assembly only 01-97 Metal leaf conductive eBay

Patents

Note that all the patents were filed by Becton Dickinson and Co, Digitran’s parent company at the time.

Number Title Filed Issued Found on
US 3750113 Capacitive keyboard 1971-11-12 1973-07-31 Capacitive keyboard types (KS, KM, KD)
US 3800104 Low profile keyboard switch assembly with snap action cantilever contact 1972-11-13 1974-03-26 Series KL snap-action conductive leaf spring switches
US 4090229 Capacitive key for keyboard 1976-09-30 1978-05-16 KM keyboards (also appears to apply to KS keyboards)
US 4408252 Low profile keyboard switch 1982-02-16 1983-10-04 KD keyboards
US 4412754 Space bar for low profile keyboards 1982-09-23 1983-11-01 KD keyboards