Thanks all for the suggestions. It was as simple as connecting a wire to Arduino's GND. My EE teachers would probably be ashamed of me. I'm now able to accurately measure batteries or the 5V pin. So thanks, it's very exciting to see the numbers you expect to see popping up on the Console.
Now back to the second topic: powering the Arduino from a battery. My plan was to basically wire the Arduino's 5V input to a 12V battery and have the GND pin connected to the 12V negative terminal. Now that I'm versed in voltage dividers, I had planned to use some resistor combination to make that 12V into 5V for the Arduino 5V pin.
In theory, this would power the Arduino and still leave me with enough GND pins to connect my circuit for reading the voltages that the battery is sending to my inverter. The two questions that I have:
- Will the Arduino need a very consistent 5V? What if the 12V goes from 12.7V to 12.3 V. Will that adversely impact the Arduino's ability to read?
- Is a voltage divider the right way to do this? I also heard mention of a PoE module, but am not sure what that is. It sounds like regulated 5V would be enough to power the board, but I want to make sure I'm not missing something here.
I'm not sure if a schematic would help here, so let me know if there are any information gaps that I can fill.