> But note: any sneak current paths from line 0 to line 1 (say) will go
> through more than one diode; only if the switch at column 0, row 1 is
closed
> will there be a path with just one diode.  If only there were some way to
> distinguish between the one-diode case and the more-than-one-diode case...
>
> So my crazy idea was to drive line 0 high and line 1 low, then read the
> state of line 0 (which, on the PIC, is supposed to reflect the actual
> voltage on the pin, IIUC).  My hope was that the input thresholds would be
> such that with one diode, line 0 would be about 0.7V and would read 0,
while
> with two (or more) diodes, line 0 would be 1.4V (or more) and would read
1.
>
> Unfortunately, it didn't work.  Even with just one diode, I couldn't get
> line 0 to read 0.  Sigh.

Use the A/D inputs of the PIC instead ?
(then you can define your own 0 and 1 voltage levels in software)

Tho I am not sure why you want to do this in the first place. It is quite
common
to read keyboards in X-Y fashion. Just not with diodes in the juncions as
you do.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.