durubay/esp32-adc-accuracy-improvement

Extracting the ESP32 ADC reference voltage to improve ADC reading accuracy

ESP32-ADC-Accuracy-Improvement

Extracting the ESP32 ADC reference voltage to improve ADC reading accuracy

The 'esp_adc_cal/include/esp_adc_cal.h' API provides a function to correct for differences 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.

NOTE:

For most boards with an on-board voltage divder of 2 series 220K resistors, the divide by 2 factor needs to be adjusted to 2.174 to allow for ADC input impedance loading the voltage divider.

The V2 code makes that correction.