Teensyfy RS232 keyboard or not?


16 Jun 2021, 17:07

I’ve bought recently a fine Bosch / Marquardt keyboard with RS232-DB9 connector.
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Both my oscilloscope and my RS232-USB converter verified that it speaks ASCII via RS232. Unfortunately, this means that <Left-ALT> is without function. The switch itself works fine.
Since I want to use the keyboard at my Mac, I need to map a key to <CMD>, <Left-ALT> would be ideal for that.
Now I consider to desolder the switches from the PCB, leave them inside the mounting plate, and solder them into a new matrix and use a Teensy as controller.
The switches - Marquardt 6184 - have diodes already built in.

I believe this project is feasible, but I’ve built only an ADB-USB and an AT/XT-USB converter so far, and I’m not too apt in soldering tiny cables onto a Teensy, and have no desoldering equipment and no experience in desoldering switches.

So, should I try to sell the keyboard and get a similar one from “Ebay Kleinanzeigen” for about 100€ with AT connector? Or should I invest into some desoldering equipment and start the conversion adventure?
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16 Jun 2021, 17:55

If it's already a full diode matrix you could just do a controller swap. You'd just desolder all the ICs, figure out which traces are rows vs columns, and wire in a Teensy.


21 Jun 2021, 11:53

OK, I’ve looked into the options “Teensyfy” and “Controller swap” (very good suggestion!) and both require more desoldering and soldering than I’m really comfortable with.
So after getting the required components (Teensy, MAX232), I’ll check/test a third option: Convert the RS232 output with the Teensy to USB and connect the <Left-ALT>-key directly to one of the pins of the Teensy and send keycodes (Mac-CMD) accordingly to the USB-host. Requires minimal soldering, but some fiddling with the Teensy-code. Wish me luck!

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