Hi Robert,
I'm using your BME280 library and it works great! By default, it uses Forced mode, correct? It takes a sample and then goes to 'sleep'? I looked at one of your calculations and that seems to be the case.
I've had just the basic Wemos and BME280 circuit on my breadboard for a couple of weeks while I worked on the Micropython code. I just froze the modules after a battle with the openSDK compilation and everything seems to be working.
About the A0 voltage: I have:
raw = adc.read()
voltage = raw * 5.28 / 1024
This calculation is giving me 3.91 volts. I measured outside and got 3.80 volts (not sure how accurate my meter is but at least 3.8 is probably accurate). So, if the scale remains proportionate (which I don't know), my factor would be 5.1315? I suppose I might need a few points, but maybe a regression is overkill.
One other thing. This is certainly not a high-priority project but the voltage seems to decrease over 30 minutes by 0.01 volt if the sky is cloudy. I have not had this run overnight yet but I suspect the battery might drain quickly. I know the Wemos is going to sleep. I'm unsure about the BME280. You also mentioned the power consumption of the voltage divider being roughly 20% of the battery's power. How long can this thing run without some sun?
I'm having fun with this. I even got solder out of two holes today with my hand tremor! using a spring-loaded solder sucker. I've never done that before.
I hope I didn't ruin anything on the Wemos by exposing A0 to overvoltage!
Thanks again for your help!