Hi All,

Ok, some updates. Thanks to all those who offered suggestions. I can't
use a port expander, but man, I wish I could!

I realized that with Bob's approach I don't think I could discern
multiple switch closures...which I will need as this is a DIP switch.
So I'm back to using a full R2R ladder. That's ok, I will somehow cram
those extra resistors in! I'm currently looking at using 10K/20K.
They're both available in 1%, 0.5%, and 0.1% tolerances, which should
be nice. Again, since I'm only trying to read 5 bits I shouldn't have
too much trouble, but accuracy would be nice.

So my question is, will this work if the rungs are not push-pull? For
this usage the rungs will be connected to an SPST switch (one of the
DIP switches). This means that when the switch is open, that rung will
effectively just be absent from the ladder.

Most examples of R2R ladders show the rungs either being grounded or
at +V. I did find this example that seems close to what I might want:

http://tronixstuff.com/wp-content/uploads/2012/02/circuit11.jpg

Thoughts? I'm interested in knowing if this arrangement will work,
plus if my 10K/20K values will be a good match for the PIC ADC.

Thanks!

Josh
--=20
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
        -Douglas Adams
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.