The first version of the voltage and current sensing module consists of 2 Arduinos: one for voltage sensing, one for current sensing. Since every Arduino only has 6 analog inputs that was the easiest to do.

The voltage measurement ist relatively easy since it is a simple voltage divider. Unfortunately I didn’t know how to measure negative voltages, but oh well…

Measuring the currents seemed a bit more tricky. The shunts were placed in high side, so I ordered some high side current shunt measurement ICs from TI called INA139. These take the differential voltage of the shunts and convert them into a constant current at a rate of 1mA/V. Since I used 0.22Ohm resistors I had to do a little math in the Arduino for conversion, but it was possible. The negative current could be sensed with the differential voltage wired accordingly the other way round.

I wanted to save some space (for whatever reason) so the pcb was shorter and had no frontpanel. I hid it behind the air ventilation board.

Following up a picture and a (pretty chaotic) schematic