This is my current (ha! get it? current? tap, tap. is this mic on?) circuit diagram for sensing the amount of current going through a shunt. I posted a question to the Adafruit forum about how to get it to work. Apparently op amps don't work well down to 20 mV of the rails. That's a bummer. Maybe I should scrap the DC shunt for a current sensor that uses a Hall effect chip to vary an input voltage.