pc keyboard to midi (without computer)

[cosmodrome]

Thanks cosmodrome, yes that is interesting too although I would want the whole thing to be as simple as possible to work with.
The idea is to create a simple version of an isomorphic keyboard like the Axis 64 (discontinued? where do you get one from in the EU?) that can be plugged in and be able to play straight away.
If I need an hdmi display to set the kbd up via a console, then that the whole thing becomes more difficult to set up and carry around. Maybe that is not a problem and setting all those commands as an autorun sort of batch process avoids needing a display, but I do not have a raspberry pi to try, nor I know anybody who does to ask.

I am suspecting that are more problems ahead for a simple device such as latency and how to map the keys to midi messages (one would have to process the key pressed to a particular look up table of of midi note on/off bytes messages, but if doable, it would be great.

Edited typo

You don't need a screen at all. You can log in on the Raspberry (or any other linux system) via network with a simple text console or small app like putty or connectbot from a PC or smartphone. Loading the right MIDI modules is done automatically when booting the board. The MIDI to keyboard mapping looks about like this:

vmpk
aconnect vmpk:0 ext:1

That's all you need to connect any kind of PS/2, USB or serial keyboard to a MIDI channel on a Linux system. Just writing this, because I know the hassle of connecting keyboard matrixes to Arduino.

[Mr_-G-]

Just an update. I have been exploring a nice little program, vmpk, which is a "virtual midi piano keyboard" that lets you use the kbd as input. I just found out that (most) pc keyboards do not allow (by design) certain key combinations (for example QTR, VZB, ZSX). So the idea of making an isomorphic input device out of a pc keyboard is, strictly speaking, not possible if one expects to play key combinations. Some of those will not work

[mjbrands]

I don't know about Mr_-G-, but the hardware is half-finished and the software still just an idea.

What would you actually use it for?