I am using an ESP8266 12 F Module with 3 x 1,2 V Batteries (3,6 Volt) I connected a chinese soil moisture sensor like this (LINK) to the anaolog pin of the ESP8266 Module. The Module works from 3,3 Volt on to 5 V.
Problem: The Sensor gives back 1024 every time no matter what the actual moisture conditions are. Dry Conditions = 1024, Fully under Water = 1024
I tried the same with an NodeMCU Module which uses the same ESP8266 Chip and there where no problems with the analog reading.
Question 1: I found out that the ESP8266 12 F has an analoge pin capable of reading only values from 0-1 Volt so this could explain the high reading on every measurement when supplied with 3,6 Volt and under wet conditions.I still don't understand why the sensor returns 1024 even if there are absolutely dry conditions. Shouldn't there be a 0 reading?
Question 2: I know that I need some kind of voltage divider e.g. two resistors and would appreciate some hint which ones I should use. The NodeMCU Module seems to have a voltage divider on board and that's why everything worked with this module.