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On Sun, Jul 31, 2016 at 11:02 PM, Albert ARIBAUD albert.aribaud@free.fr wrote:
Le Sun, 31 Jul 2016 21:56:13 +0100 Luke Kenneth Casson Leighton lkcl@lkcl.net a écrit:
Hmm... Not getting what you're hinting at. Can you develop?
it's related to mis-detection of keys. if you press certain combinations in certain ways, you get "ghost" keys that you can't tell if they were actually pressed or not. by reducing the number of keys that are "live" (16 fan-in only activates up to 8 maximum where as 8 fan-in could activate up to 16 maximum) you reduce the possibility of "ghosting".
there was an article online about it... ah! found it: http://pcbheaven.com/wikipages/How_Key_Matrices_Works/
Ok, got your point now.
Too late today to do probabilities (heck, even in the morning right after my coffee shot I would not trust my skills in probabilities). Still, I intuitively (yeah, I know) think there is no reduction in the risk of ghosting when transposing the matrix, because there is no asymmetry in the ghosting problem; ghosting occurs as soon as three of the four connections between two rows and two columns are closed: at that point, there is no way to tell whether the fourth connection is open or closed, and this, regardless of any notion of "row", "column", or "activity".
IOW, whether or not a given state of the keyboard matrix will exhibit ghosting is only defined by the distribution of the depressed keys on the matrix, not by the rotation with which we look at that matrix or whether it currently has an active column.
my point is: if you've activated 2x the amount of keys because you're firing on "rows" (16 activated) instead of "columns (only 8 activated), there's now 2x the chance of having a "ghosting" problem.
i think.
too much for my brain to cope with....