Having started out with the 5V based Arduino Nano, I needed to make some adjustments to make my circuit work with the Nano33, which runs at 3.3V. I thought I would have to adjust the voltage dividers, but at a ratio of 10:1 (100kΩ and 10kΩ resistors), they leave me with a maximum input voltage of 36.3V, which is more than enough.
This only left me having to adjust the voltage supply and the output of the ACS712, as described in an early post. For the supply voltage, I went with a simply 7805 linear voltage regulator. The smaller TO-92 version would've been fine, but I didn't have that on hand. For the output, I went with a 1:2 voltage divider (10kΩ and 20kΩ), which gets the 0-5V levels nicely down to 0-3.3V.
The firmware needed only minor adjustments, in the ADC readout calculations. It worked find when switching the Arduinos without any battery or grid connected. Unfortunately, when I tried to connect the local side, I seem to have gotten the positive battery wire caugth on one of the resistor legs that was connected to the Arduino's analog input pins. Turns out the Nano33 IoT doesn't like 12V on its input pins, so it let out a small poof, a bit of weird smell, and the magic smoke was gone 
Bye bye, little Arduino.
Top Comments