Jim Sokoloff wrote:
> <snipped short>
> Now, being a lowly mechanical engineer (:-)) I can't see HOW to install
> diodes in the above to ensure that you could detect arbitrary chording.
>
> Would you mind re-drawing the ASCII schematic with suitable diodes in
> place for the silicon-challenged?
>
> Thanks,
> ---Jim

  Easy.  I'll simplify to just one 3-switch bank, though (Lest I get
griped at <G>)

 Vcc O-/\/\/\-+
       (20k?) |
              |
  A  O--------+---+------------+------------+
                  |            |            |
                  V            V            V
                 ---          ---          ---
               D1 | ___     D2 | ___     D3 | ___
                  +-* *-+      +-* *-+      +-* *-+
                    A1  |        A2  |        A3  |
                        O            O            O

                        1            2            3

  So if A1 and A2 are pressed, when you pull pin 1 low, or pin 2 low, A
will be pulled low - but when you pull 3 low, the pullup keeps A high.
(So long as pins 1 and 2 are tri-stated, or high.)

  Also, when you don't have tri-state logic attached to pins 1, 2, 3,
you can have real problems if 1 is high and 2 is low (or vice versa)
when both A1 and A2 are pressed <G>

  I hope this helps!

  Mark, mwillis@nwlink.com