If you unplug A6 and A7 from everything, what voltage do get if you put a voltmeter on each pin?
Am I to call A6 or A7 in the sketch ?
I set A1, A6 & A7 to be called in the sketch, dis-connected the pins and got voltages with my meter.
A1 = .4v A6 = 1.6v A7 = 2.3v
Next I re-wrote the sketch to not call A1, A6 or A7, and ran it.
A1 = .5v A6 = 1.6v A7 = 2.4v
I'm not sure what these voltages show, but it's clear calling them in the sketch makes no difference.
I dis-connected everything.
Took out another Nano (one that i had tested in the rig but hadn’t made any difference).
Set the second Nano on the breadboard, along with another OLED.
Jumpered all the connections.
Fired it up. It works.
Breadboard version works, soldered version does not.
I had scrubbed that board with alcohol, and checked it for shorts. The only thing I can figure is that maybe there was a short somewhere else, that I hadn’t found. Or maybe enough resin was still present to give squirrely results.
I have decided to make some PCB’s that I can mount my Nano’s on, that have solder pads a ways apart.
I want to thank each of you who tried to help me. But short of your seeing the soldered rig yourself, you couldn’t have know it was a fabrication error somewhere.
If Nano is powered thru USB, about 0.3V is dropped by the reverse polarity diode, so AREF is about 4.7V, so 3.3 * 1024 / 4.7 = 718.978723404.
I had scrubbed that board with alcohol, and checked it for shorts.
Did you use solder paste/flux (bad) to solder the pin-headers on the Nano.
No. I cut down a discarded PCB that had a nano footprint and thru holes on it. I sawed it down to size and cut the traces. I then soldered two headers onto the board so I could change out the nano if necessary.