I really want to get a mechanical version of n-key rollover keyboards, but commercial ones are too expensive, so I decided to build it up myself. :D
The idea was starting from this article.
http://www.dribin.org/dave/keyboard/one_html/This article is verified with this little experiment - using arduino (simple embedded system) + 2x2 matrix setup
http://www.youtube.com/watch?v=4-QCBUkoldEyou can see this accepts any combination of the key stroke without ghosting.
Now it's time to roll!
Sorry for Koreans in the image. It is -
1. Cutoff the patterns on the row-side circuit.
2. Scratch the coating over the copper so that naked copper surface is exposed.
3. Surface mount the Diode (the direction should be considered depend on how controller is built. In this case, the diode direction is row->col). In lower one case, additional rewiring needed.
diodes. - SMD type 1N4148
Pattern cutoff and fluxed
Mount the diodes
Mounting done
I used the LIMKB controller(A custom keyboard controller built in korean keyboard community,
http://otd.kr) without ghost check logic.
As the result, I could get the USB version N-key rollover Apple Standard I. It works very well. (Although I can input only 6+1 keys due to USB keyboard protocol)