I needed a way to accurately measure current draw over time for devices drawing a few or tens of milliamps. Rather than buy expensive test gear I just threw together three parts from SparkFun:
...a little math and presto! I have a tiny little Coulomb counter that shows current draw and direction and can sit right on a breadboard.
(is that hot glue? Yes, yes it is. Don't judge and don't ask what's holding the OLED screen to the PCB)