A while back HD posted about using diodes as cheap temperature sensors:
https://hackaday.com/2018/04/16/two-cent-temperature-sensors/#comment-6192482

But chasing mV sized forward voltage deltas is hard to do with the limited ADC on most mcu's. Our LED light-sensing experiments demonstrated that timing reverse-bias decay with the Input Capture Unit on an Arduino is easy to do, and provides high resolution temperature readings from a single diode without any amplification:

 https://thecavepearlproject.org/2019/11/04/single-diode-temperature-sensor-with-arduino-icu-via-reverse-bias-leakage/