but not the same as, as the keyboard I had.
What’s old is new again! https://hackaday.com/2019/11/18/optical-keyboards-have-us-examining-typing-at-light-speed-ish/
40 years ago, I was given an old keyboard from my high school teacher, the SP-251 (don’t know the vendor). It was optical. There was a anodized black metal plate inside the keyboard with 13 channels running left to right. The left side of each channel had a small incandescent bulb. The right side had a CdS photo cell at the end of each channel. Along the top was a metal rod which held the top end of the metal bars attached to each key. Each of these bars ran top to bottom with a spring to keep them up out of the channels. Each key had a different combination of tabs that protruded downward, so that when a key was pressed, the tabs broke some of the beams, encoding the value of the key. Strangely, the bit coding of these tabs was not ASCII nor the older EBCDIC, as far as I was able to tell at the time. In hind sight, it clearly is not.
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