Plan for NKRO in a Model M

[Panter]

Although I love a good summary, I couldn't help myself but read all 22 pages:P
The only question I have is whether there is a possibility to still connect this keyboard to an old ps/2 port? I have two computers, one old and one new, and really want to use one keyboard for both the computers.

No, you cannot without a converter. The xwhatsit controller is USB only. You would need a USB to PS2 converter. I do not know if they exist

It might be possible to make a usb keyboard work with the specific computer I was talking about. That said, my current challenge is to actually find a model M:P But thanks for your information, I will keep an eye on your project, and might actually end up buying one of your PCBs

[wcass]

...
The only question I have is whether there is a possibility to still connect this keyboard to an old ps/2 port? I have two computers, one old and one new, and really want to use one keyboard for both the computers.

I guess the "old one" is pretty old. USB was relatively common 20 years ago. There may be no external ports, just an internal USB header. Check your motherboard documentation. If it has a free PCI slot, you might be able to add an expansion card, but make sure your OS will support USB and the card.

[HuBandiT]

Anyone still interested in this? I have a few ideas I'd like to try (one of them might work just by a controller replacement), but I would need cooperators.

[andrewjoy]

I don't think Nkey rollover is required in the M but a higher rollover would indeed be handy as its technically only 2key roll over and that is too low, 6 key would be plenty .

[HuBandiT]

Alright, I see your point; we'll see how many KROs we can manage to get out of it. So you are interested then?

[andrewjoy]

Possibly , but i don't use M's that often more of an F man myself

[HuBandiT]

Fs are good indeed, am I am planning to work on them as well, but there's little challenge in making Fs NKRO.

[hasu]

How about adding thin film between membranes as an insulator and sensing capacitance?

[XMIT]

How about adding thin film between membranes as an insulator and sensing capacitance?

I don't think the pads are large enough. Capsense is tricky business, if I've learned anything reading wcass's and idollar's design threads. Things work best with large pads, small traces, and minimal overlap. The Model M membranes fail on all three counts. It's a neat idea though.

A diode needs to be in series with each switch for true NKRO. A thin film of diodes is certainly the right approach. The secret ingredient is niobium silicide.

This was demonstrated in 2014:

From: http://www.pnas.org/content/111/33/1194 ... nsion.html
See also: http://www.pnas.org/content/111/33/11943.full.pdf

Good luck making one. It's a long shot just for an NKRO retrofit for a Model M but it could enable arbitrary rubber dome matrix boards to be NKRO. Why in large quantities it could even be cost saving.