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KBK update for Sunday, 11th April

Another day, another largely forgotten vintage keyboard manufacturer. This time, it’s Control Devices, Inc. Control Devices invented possibly the most convoluted capacitive system, one that required (in addition to the variable capacitor) a transistor, a fixed capacitor and two resistors for every key. These small circuits then drove a diode matrix, which was then fed through a sense amplifier to yield adequate signals strength and a synchronisation circuit to wait for all the sense lines to settle before the output code was delivered. The small circuit within each key station provided each key with its own capacitive sensor. One of the inventors, Donald Gove, was the inventor of the IKOR self-encoding capacitive switches mentioned recently.

A couple of people have come across Control Devices keyboards, but nobody was ever forthcoming with details or illustrations. Some instances were described as “foam and foil”, which raises an interesting question of whether they moved on to more “conventional” capacitive keyboards (using a matrix scanner to centralise the capacitive sensing circuitry), or whether they merely simplified (or cheapened) the variable capacitor portion but retained the per-key capacitive sensors.

View within the updates for 2021

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