But......I thought this problem WAS a nail! 8-)
I did try 4 different keypads that have resided in my junkbox long enough to have
accumulated some dust and maybe even corrosion. You are right, one of them (an
escapee from a long dead calculator) did show intermittent decoding, but after a bit
of exercise it now seems more reliable. I built the initial resistor matrix external to
the keypad so I can try different keypads. Maybe it would be worthwhile to try
making a discrete switch based keypad from 16 of the tiny push-switches that are
available for less than a cent each on Ebay?
Long ago I purchased a few keypads which have plastic domes that click over-center
and make hard mechanical closures (with lots of contact bounce). If I can find them
they will get tried in the present testbed. Might be interesting to see what is required
to debounce those antiques.
Being an ancient telephone engineer the concept of "sealing current" comes to mind
as a possibility for use based improvement of questionable keypads. Another option
is that they are usually very inexpensive and thus the bad ones can be trashed with
This is fun! 8-)