Sensed current timed with a 555 that controls an H-bridge integrator.
Pulse rate on output pulled up to 3V3 is function of current flow in sense resister. Integrating current significantly reduces MCU activity while retaining measurement accuracy. The pulse can be counted to gauge a battery (state of charge), or timed with capture hardware to calculate the current rate.
Coulomb counters are important for batteries that have a flat discharge voltage, e.g. the voltage doesn't change very much with state of charge in LiFePO4.
H-bridge drive signals need flipped for reversed current in sense resistor.
