I'm interested in exploring this idea, because I am trying to come to grips with differential measuring. Here is an earlier thread:
With your idea Bob, I see a problem with resolution. Say we are drawing 55 mA, and we have a 1 ohm shunt. That means we drop 55 mV over the shunt, which is then halved by the voltage divider (22.5 mV drop). The resolution of analogRead is about 5 mV, so we are only going to get 1 "count" per 5 mV (10 mA of current drawn).
I am wondering how you might connect up an op-amp to amplify the difference (eg. convert the 55 mV to 550 mV). What wiring would you use that wouldn't somehow short out the op-amp or something? And how would you set the gain up?