\ \Just get an accurate input resistor and use a current-to-frequency \converter type of ADC. Then, a long gate time gets you \part-per-million resolution, while a shorter gate time gets you \the appropriate resolution for that 0...5V range. \To do it with a single-chip micro's ADC, you have to go through \a lot of hoopla to keep the input potential in the ADC range \and that means multiple calibrations (for the different ranges \and offsets).
This sounds like a neat idea, I'm using an Arduino for my experimentation and I'm not sure if I could get it to time the gate and count the pulses. I don't know if using an interrupt to count the pulses would mess up the gate timing enough to throw too much error into the readings. I guess I could store the start time, count pulses in the foreground until a set amount of time elapsed, I should be within 1 count if everything works correctly.
RogerN