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Cherry solid state capacitive

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US designs

Solid state capacitive is a family of foam pad capacitive keyboards from Cherry. A 1983 full-page Cherry advertisement describes their DIN-compliant implementation as a “foam pad capacitive keyboard”. All known models offer hysteresis. The DIN-compliant type is described as having a “snap-in angled foam pad for hysteresis”; this characteristic appears to be new as of the DIN-compliant design, as diagrams in the Cherry catalogues of the higher-profile type do not show an angled pad.

Pre-DIN types

According to Computerworld, 28th May 1979 (NCC preview page 61, document page 101) Cherry would be exhibiting its then-new solid-state keyboards at the 1979 National Computer Conference in the United States. These were models CB80-07AA “secretarial” and CB80-12AA “communications”, as described in the 1979 Cherry Keyboards catalogue. Both of these keyboards were included in the price list from the 1st of March, 1979. However, Cherry capacitive solid-state keyboards have been found advertised as far back as June 1977. The 1979 design used a custom LSI circuit from American Microsystems and a read-only memory from Cherry Semiconductor, according to the advertisement in Electronics magazine. No examples have been found with a Cherry Semiconductor ROM, but AMI (American Microsystems) encoder chips were standard issue.

There are no known patents for the switch design itself; the patents below cover enhancements to the pre-DIN product line:

Patent Title Filed Published Product
US 4188136 Keyboard switch actuator and locking assembly 1978-01-19 1980-02-12 Space bar stabiliser (as seen with M6) and solid state capacitive secretarial shift
US 4445164 Lighted key module assembly 1982-05-05 1984-04-24 LED attachment to pre-DIN solid state capacitive

By 1982, CB80 series had been renamed B4V series, with the existing models changing to B4VE series models B4VE-9501 and B4VE-9601 (per the 1982 catalogue).

The original solid-state keyboards are fairly uncommon; they were introduced only a couple of years or so before DIN standardisation led to Cherry producing a reduced-size version. DIN-compliant models are more commonly encountered. The pre-DIN types did however see use with a number of manufacturers, as noted on the master vintage Cherry keyboards list, including keyboards for the Crumar GDS, ADDS Regent 25 terminal, an unidentified NCR terminal (keyboard model B4TE-8301, NCR part 189-1108238 REV.E), the CDC 721 and Kroy 80K. The switches in B4TE-8301 are NCR blade mount; there are no publicly-available photographs to depict this however.

Observed features for the pre-DIN product line include:

Alternate action and secretarial shift can be seen in UncleFan’s CB80-21AA keyboard of unknown origin, made around 1979 or 1980.

Unified type

A single example has been found of a unified design that uses a plastic “barrel plate” (plunger guide shaft panel) instead of discrete plunger models. Keyboard part B5AB-7701, date-stamped December 1980, was found in an ADDS Regent 25. This module has ADDS customer part number 355-09500 REV. 4, which is the same part number used in a slightly older Regent 25 on what appears to be a more conventional plate-mounted keyboard. This unified type appears to be a cost-saving replacement that is compatible with the older design.

The general appearance of this type, when viewed from above, is fairly similar to the Mitsumi KSR Type keyboard used in the Commodore 64, with cruciform mount plungers in a barrel plate, surrounded by external return springs.

Series MF

In their switches advertisement in Electronic Engineers Master Catalog 1985–86, right at the bottom of the final page, Cherry depicted Series MF pad capacitive switches. Series MF appears to match the DIN-compliant solid state capacitive switches. Whether the pre-DIN foam pad switches were also Series MF is not currently known. The “F” in MF appears to correspond with the keyboard model prefixes of KF and BF for capacitive keyboards.

There is no known patent for the DIN-compliant design as found; the patent shows a dual-stage cylindrical/conical spring instead. The patent does however note, “Thus, for example, a foam pad with an electrically conducting film may be employed as a movable capacitive element without departing from the invention.”

Patent Title Filed Priority Published Product
US 4466046 Capacitive keyboard switch 1982-05-17 1983-04-06 1984-08-14 DIN-compliant design using a spring instead of foam pad

Japanese designs

Hirose Cherry filed Japanese utility model S56-90322 “容量形無接点スイッチ” (“capacitive interface switch”) in December 1979. The focus of the utility model appears to be the addition of a tactile leaf within a foam pad switch. They would later file Japanese patent S59-828 “静電容量形キーボードスイッチ” (“capacitive keyboard switch”) in June 1982 for foam pad capacitive switches.

Only one such keyboard is known, FRICS model NDC-502. The switches with integrated LEDs are linear, while the remainder of the switches are tactile, using buckling rubber sleeves almost identical to those in Key Tronic keyboards.

Keyboards

Keyboard Hirose part Switch Date Reference
FRICS Key Board NDC-502 CB25-1632A Rubber tactile 1986 Imgur

Documentation

All documents scanned by Bitsavers unless otherwise noted.