This code is written to assist you in calibrating the ESP32 Analog to Digital converter. While newer chips are factory calibrated, older chips rely on a default VRef value and most of the time have poor ADC performance.
This tool is based on this forum post : https://esp32.com/viewtopic.php?t=8774#p36882 .
Performing an ADC calibration involves burning fuses, which is an irreversible operation. Use this code at your own risk.
Open this project with PlatformIO and upload to a ESP32 board.
Open a serial console at 115200 bps on UART0. Then follow the instructions.
The workflow is the following :
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Apply 150mV to GPIO25 (ADC2) and GPIO34 (ADC1). It is advised to add a decoupling capacitor next to the pins.
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Apply 850mV to GPIO25 and GPIO34 when requested.
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Burn the calibration data into eFuse using
espefuse.pytool and the values printed on the serial console.
For ADC1 the accuracy improved in the 0.2-2.5V range. Outside this range it seems that two point calibration is not used.