Keyboard rewiring question:

[Charlie]

Right I've got my case-modding bug back:
Today the task is to turn a retro-keyboard into a PS2 one for connecting to an x86 motherboard...
...this is a really boring task which I genuinely hate:

1) Take old PS2 keyboard & disassemble.
2) Draw up a row / column grid for the membrane so I know how the decoder works.
3) Draw up same for retro keyboard in the hope that they match...
...that will be a 'No'.
4) So I'm going to have to fully rewire the retro-keyboard to match the row / column grid for the PS2 one.

I've done all this once before and though amazingly dull + fiddly you do get your retro-keyboard to output the correct key codes via PS2...
...that can then be wired into the header of the motherboard you really want to use.

So where's the question?
This time I'm building an x86 Oric Atmos - it really doesn't have many keys to play with but does have a function key. So I'm going to need to use that function key to map the important missing ones to the available keys.
eg:
1-9,0,-,+ becomes F1-12, along with a few others.
Of course the donor keyboard doesn't do that so I must switch the lines prior to the encoder chip getting it...
...the Atmos keyboard essentially becomes wired as two keyboards:
The standard one and the one selected by the function key.

With me so far?
Good.
Now, I was considering doing this as a mechanical bodge - the function key has two switches in it; one for up & one for down. But it would be much neater to achieve this electronically:
-Default layout when the f-key is up.
-Alternate layout when the f-key is pressed.

Can anyone point me in the right direction for info on making such a switching circuit?

Thank you!

[alexh]

If it is not solely about the experience could you not use an off the shelf system like a KeyRah? It uses all of the electronics in the host keyboard and converts to USB? If you can get the specs you might be able to ask Jens nicely to modify the firmware for the Oric keyboard or show you how to reprogram the PIC/uController?

[Charlie]

Now that, alexh, is a very good idea - so good in fact that I asked Jens that very question some months ago.

In all credit to him he was actually willing to help. The trouble is twofold:
-I'm an awkward b*gger and would rather do it myself.
-More importantly once I've crammed a fully-functional x86 PC into an Atmos case there really isn't going to be room for a KeyRah. There's just enough space for the electronic gubbins out of a keyboard.
-I need PS2 for what I have planned, not USB...
...Ok, I could wire in an adapter but that would be more space taken up.

What I'd REALLY love is a (very small) programmable keyboard adaptor:
-Plug it in to your reto-matrix
-Press all the key-combinations in turn, telling the adaptor what it should output for each said combination.
-Job done!
Sadly I'm not aware of such a beastie so I'm reduced to doing it the hard way.

[alexh]

Ah, I thought you just wanted to use an empty Oric1 as a keyboard.

[Charlie]

I have moments of madness, though I prefer to call them flashes of inspiration.