Generic Calculator Shield for Arduino Photo-journal

[everettr]

(03-24-2015 03:07 PM)Marcus von Cube Wrote:  This sounds interesting. Can you explain the trick in some more detail? Will it allow the detection of keys being pressed simultaneously (n-key roll over)?

I think that mattiaspaul is referring to what is sometimes called, "Charlieplexing." Here is a link to the Wikipedia article: Charlieplexing
Here is a link to an article in Electronic Design

For the 4 I/O pins plus 4 diode configuration with 12 keys, there is some ambiguity as to what keys are detected when multiple keys are pressed together. Using 4 tristate I/O pins with 12 diodes supposedly removes all of the ambiguity, so you would have 12 key rollover for your 12 key keypad. I haven't quite understood how the 4 trits of information for the I/O pins (81 states) maps unambiguously to the 4096 possible keyboard key combinations.