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Cherry reed switches

Contents

Overview

Cherry filed a patent for a tactile reed switch in July 1970. US patent 3644855 was granted in February 1972. It seems that this switch was only marketed for a brief time: it was included in Cherry marketing literature in 1971, and no longer mentioned by 1973.

The design given in the patent achieves the tactile feel by way of magnetic separation. A metal disc embedded into the switch attracts the magnet and stops it moving. After a spring above the magnet is sufficiently compressed by the operator via the plunger, the force within that spring becomes great enough to force the magnet off the disc. There is a separate main return spring placed under the magnet. An article Code your own keyboard in Electronics in August 1970 (see Documentation, below) describes a kit keyboard designed around these switches. The tactile feel is described in the subheading of article, as “pressure buildup and release in each key lets operator feel when data enters”. This is elaborated further in the article:

One unusual feature of the unit that aids the operator in typing in data is “keys that feel.” Each key comprises a spring and magnet assembly which exerts an upward force against the operator’s fingers. When the key is being depressed and travels a certain distance, the magnet’s threshold is overcome prying it loose. The force against the finger is released and a click sounds indicating the transfer of data.

The reed switches are tall, with a distance of 1.12″ (28.4 mm) from the top of the PCB to the top of the plate, and 0.06″ (1.5 mm) of the shell above the plate.

Keyboards

Thus far the only known instance of these switches is in the kit keyboard described in Electronics. 261/262 mechanical switches followed the next year, and it seems that the reed switches had a short sales life before being discontinued.

Models

Cherry reed switches used the old model numbering system; only the following models are known:

Model Type
201-0100 SPST-NO
202-0100 DPST-NO

Specifications

Operating force 2.5±0.5 oz
Pretravel 332±132″ (also given as 0.093±0.031″; approx. 2.4±0.8 mm)
Total travel 316″ maximum (approx. 0.188″, or 4.8 mm)
DC resistive load 7 W maximum
AC resistive load 12 VA maximum
Current 0.25 A maximum
Voltage 28 V maximum
Bounce time 1 ms maximum
Initial contact resistance 250 mΩ maximum
Rated lifetime 10 million cycles minimum

Other reed types

Examination of back issues of Electronics magazine has revealed that Cherry also introduced a series of reed snap-action switches, called “snap-reed”. Advertisements depicting snap-reed switches do not give the series name, but a plain text advertisement does list E66 series as a snap-reed type. The snap-reed type is first known from December 1966. There is little if any other trace of its existence, and it seems that it was comparatively short-lived, just as the reed keyboard switches were.

Documentation

The documents below were scanned and made available by Bitsavers unless otherwise noted. The Cherry flyers are listed there under Cherry components.