How about a series arrangement instead of parallel? Wire four resistors in =
a=20
1/2/4/8 ratio in series, each of which can be shorted by one of the dip=20
switches. A fifth 'source' resistor to +V provides an 'almost current=20
source' by being significantly larger than the 1/2/4/8 resistors. If you=20
could get away with the fifth resistor being arbitrarily large you could ge=
t=20
as close to linear as you want. The trade off is the full-scale output gets=
=20
progressively smaller as the fifth resistor gets larger.

A quick spreadsheet shows that with the values in the ratio

1/2/4/8 + 16

then the full scale value is about 48% of +V
and the minumum delta between two adjacent values is about 1.7% of +V. This=
=20
corresponds to about 17 ADC counts.

My spreadsheet seems to indicate that the ratios above, including the 16 fo=
r=20
the 'source' resistor, results in the maximum value for the minimum delta=20
between two adjacent values, which makes sense to me.

-- Bob Ammerman

--=20
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