How many bins can I code using a resistor on an ADC
If you use E192 0.5% resistors then there are 192 values per decade.
If you set each decade as A/D full scale (ie 2.5 V) then the values are 4096/192 apart --> 21 * 0.6 mV --> 12.6 mV apart. So easily discernable by your A/D.


Test which decade a resistor is in by setting a current (or simply a series resistor) so the top value of the decade is 50% scale (1.25 V). The voltage should be between 10 and 2047. If the A/D output value is less than &lt; 10 or > 2047 choose a higher or lower decade to test. 
Once you know the decade, set the measurement current to get full-scale with the largest resister in the decade. Measure the A/D value to identify the bin. 


You should be able to measure at least 3-4 decades with little complexity and using a single purchased resistor giving a practical number of bins around 768.

You could do the same with E96 1% resistor values and get 384 bins in 4 decades.