William Bross wrote: > Can you flip the circuit around so the single resistor goes to ground > and Vdd is sourced to the four switchable resistors? If so, it makes > calculating the divider ratios easier. Huh? It's the same thing, just with the Vss to Vdd range flipped. Either way the A/D can read the signal and the firmware has a equal chance of making sense of it. Neither way is more "right" than the other. One approach to Joe's problem is to think of the switches as bits of a D/A and wire them up in a R-2R ladder. That spreads the values out evenly and doesn't require several strange resistor values. You can chose any two 1% values with a 2:1 ratio over a reasonably wide range. At one end you want to not exceed the A/D's input impedence requirement. At the other end, you don't want to draw excessive current. To limit current, you could turn the whole thing on only for a short time around taking the measurement, and use something nice and simple like 1.00K and 2.00K ohm resistors. ******************************************************************** Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products (978) 742-9014. Gold level PIC consultants since 2000. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .