HP 2645A keyboard USB conversion


28 Oct 2019, 04:18

I finally got around to doing this. I used QMK as the base, since that seemed the best way to make it generally useful, with its fairly general key mapping and other support. I could imagine someone someday using Circuit Python to build a vintage keyboard tookit with common decoding routines, equivalent key mapping, REPL debugging, and maybe even rudimentary logic analysis. But for now, QMK is what we have. The converter is in my fork.

I am pretty sure I used one of these keyboards on some TENEX system connected to the ARPANET back in the day. I remember the funny mix of key shapes. Maybe at BBN or ISI? The one I have now though I picked up surplus much later. As far as I can tell, it is in complete working order. The locking mechanism on the locking keys being the most fiddly.

I always try to use as much of what remains as possible. So, here that means the usual interfacing to 74-series TTL, and not directly to anything more complicated, as others prefer to do. Still, since the key switches are Licon magnetic valve, the keyboard has a ramp generator that requires ±12V, in addition to TTL's 5V. I used a boost converter bought off the Internet for USD 3.00, powered by a second USB port.

The cable for connecting to the terminal has a 30 position edge connector. (See Haata's photos of his, which are much better than any of my photos.) Mating connectors are also only around USD 3.00 a piece. But Digi-Key had a minimum order quantity, so even when I build a tidier version on a perfboard I will have some left over. I know these keyboards are still reasonably common. So, if anyone here in the States has an HP 264xx keyboard and wants a connector or two, drop me a line.
hp_264xx_usb.jpg (443.45 KiB) Viewed 1140 times
Last edited by MMcM on 28 Oct 2019, 05:29, edited 1 time in total.

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28 Oct 2019, 04:44

Nice work!

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