Posted by matt(v) on August 08, 1999 at 02:20:08:
In Reply to: Asking 1 last time. Diode and key board hack? posted by Jim M on August 08, 1999 at 00:23:52:
We aren't ignoring you, we just don't want to give you bum advice. Since you seem desperate here is my take on the issue, I messed around with diodes extensively.
I have hacked three different keyboards, tried diodes with all of them and had the same result every time, at first I thought I was just stupid. People far, far smarter than me have said that diodes should fix all your problems
As you probably know (you better know) you get a keyboard jam/ghost when you press down three keys that form three corners of a rectangle*, some keyboards "ghost" at this point and act like you also pushed the 4th corner key. Some keyboards "jam" and refuse to accept this third keypress (internal speaker beep)
*when I say rectangle I mean matrix rectangle, the circut on the mylar under the keys, just because the keys are laid out nicely on the keyboard, don't expect the electrical matrix that contorls them to be laid oth the same way (it never is)
Anyway the upshot of all this is that by adding diodes in line with each key you want to press you should be able to forget about jamming and ghosting altogether.
But in all my trials I have only been able to get this to work for ONE EXTRA key, that Is by adding diodes you can prevent the first ghost or jam but if you do anything after that to cause another ghost/jam at the same time as the first the matrix becomes completly overloaded and you get a ghost/jam anyway.
So as far as you are concerned, if you aren't able to map out a matrix with enough Un-ghosting keys to give you all the inputs you want, adding dioded is only going to give you one more.
Now I'm no electronic genius, I know which end of a soldering Iron is hot and not much more, maybe diodes work for others maybe they dont (but they sure are keeping quite about it) all I am saying is that they don't work for ME
If you understand how a keyboard works you should have no trouble finding enough keys that don't jam. 22 off a keyboard is my record.
hope this helps
Matt(v)