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Generic Calculator Shield for Arduino Photo-journal
03-24-2015, 04:53 PM (This post was last modified: 03-24-2015 06:50 PM by everettr.)
Post: #40
RE: Generic Calculator Shield for Arduino Photo-journal
(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.
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RE: Generic Calculator Shield for Arduino Photo-journal - everettr - 03-24-2015 04:53 PM



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