Ah, I just realized the schematic in the github is not the most up-to-date — there was a minor update that adds the current sensing circuit. I will check that in soon. Attached here is the current sensor part that’s relevant. I just used a low-cost LM358-based precision rectifier circuit. What you have designed is probably more sophisticated and accurate that mine. Note that the GND pins on the zone expander connectors are also connected to the current sensing resistor, this way all stations on the expansion board also return current through the sensor.