But before I go there, I just want to test my sketch with some fixed resistors. Building a simple voltage divider on A0 using two 5K resistors I don't get a reading on A0 of 512 as I would expect. I get ~561.
The two resistors I am using both read 5.08K on a DMM so they should be pretty equal.
I tried two 1M resistors also (1.055M and 1.025M on the DMM) and I get 222 on A0.
I understand there is a 220/100 voltage divider built onto these NodeMCU boards between their 3.3V A0 and the 1V A0 of the ESP2866. Is that voltage divider causing these readings? If so, how do I normalise an external voltage divider across the internal one so that I can actually calculate the resistance of what is going to be my variable resistor in the form of a 1M thermistor?