I am using an Arduino Due with an AC-AC 9v adapter for the voltage sense, project is based on: https://boredomprojects.net/index.php/projects/home-energy-monitor
except that I am not on 3 phase power, I am in the US. So I am using the official emonlib.
The first few minutes that it ran it was +/- 0.1volts with:
emon1.voltage(0, 161.9, 1.7);
I then walked away for about an hour, when I came back the voltage was fluctuating +/- 0.3 and I had to increase the 161.9 to 162.3 to have an accurate voltage.
I am not sure what this means, as far as I why did I lose some accuracy, and why did I have to increase the calibration number when it was very stable previously.
While I am Calibrating the Arduino Due I have it connected to my PCs USB port via micro usb cable, so this is also what is powering the Arduino Due.
Once I have it calibrated I plan to power it with a 5V micro USB power adapter. model F06US0500100A:
Any help Dialing it in so that I lose as little accuracy as possible is appreciated. One thought I had was what if my computers 5v from the USB is not great? does the Arduino Due buffer it good? I know it has to reduce the 5v to 3.3v.
EDIT: just tried a different USB cable as well as a USB3 port instead of USB2, this had no effect, so I am going to guess that the difference in accuracy that I now have has to do with the AC-AC adapter, possibly it lost some accuracy once it warmed up?