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KBK update for Thursday, 12th March

At the end of the 1960s and the start of the 1970s, manufacturers were finding a surprising number of ways to design switches that could directly address logic circuitry without contact bounce. The earliest known dedicated bounce-free keyboard switch type was Micro Switch SW using Hall effect, introduced at the end of 1968. Licon put out Series 550 ferrite core (“magnetic valve”), that goes back at least as far as the end of 1970. Perhaps the strangest was Mechanical Enterprises Mercutronic, a family of designs that used mercury-containing tubes for switch contacts, available for keyboard applications from around 1970.

RAFI used Hall effect from around 1973, in the form of RC 72 series. This was not their original contactless switch: an older design is known from patents, using magnetoresistance, that has yet to be encountered. Fortunately RAFI still have a 1972 catalogue documenting these switches. RAFI magnetoresistive switches appear to have no series name, only part numbers; they are described simply as “contactless”.

These may well not be RAFI’s oldest keyboard switches, but this is the oldest catalogue that RAFI were able to find, and both this and the RC 72 catalogue defied the odds against being recovered.

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