a 3.3:1 potential divider.(Vcc - 33k - A9 - 10k - GND)
I'm trying to build a unit to display the USB voltage. I've tried the "secret voltmeter" - see my other post.
Link to other thread:https://forum.arduino.cc/index.php?topic=636038.0;topicseen
Sorry Paul, its two completely different approaches to making the same measurement.