Extracting the ESP32 ADC reference voltage to improve ADC reading accuracy. The 'esp_adc_cal/include/esp_adc_cal.h' API provides an API to allow for corrections in measured voltages caused by variation of ADC reference voltages (Vref) between chips. By-design the ADC reference voltage is 1100 mV, however the true reference voltage can vary from device-to-deice and range from 1000 mV to 1200 mV amongst different ESP32's. Reading the reference voltage enables a correction to be made which then improves ADC reading accuracy.
There is also an example for the Lolin D32 board with on-board /2 voltage divider (code V2).
Code: https://github.com/G6EJD/ESP32-ADC-Ac...