Deous:
I have tried DS18B20, LM34, MAX31855.... they don't work - I get random readings no matter what.
Tried different boards Uno, Mega, STM, ESP32.
Everytime I get different bad readings. Maybe all those circuits are bad or defective....
More likely: you do something wrong, or you use the sensors out of their range.
All I want to do is measure temperature with low degree values - like going to -100C. Range let's say -200~200C
What is the best temperature sensor and thermocouple for that? What would you recommend?
NTC.