ADC Range Extension Solution

[中文]

Important

The current ADC extended range solution is only applicable to ESP32-S2 and ESP32-S3 chips.

The ESP32-S2/S3 ADC, within its default range, can handle most ADC functionalities such as key input and battery voltage detection through an external voltage divider circuit. However, for applications like NTC measurements, full-scale measurement (0 ~ 3300 mV) may be required. By configuring the registers to adjust the ADC’s offset voltage and applying a nonlinear compensation method for the high-voltage region, we can extend the range of the ESP32-S2/S3 ADC.

The process is as follows:

  1. Measure the first voltage value using the default offset

  2. If the measured voltage is less than the set voltage, directly output the measured voltage as the result

  3. If the measured voltage is greater than the set voltage, increase the offset voltage, perform a second measurement, apply nonlinear correction, and output the corrected value as the result

  4. Restore the offset value once measurement is completed

Overall, during each ADC measurement, there will be 1-2 times ADC reading. For most application scenarios, the measurement delay introduced by this scheme is negligible.

Note

For the ESP32-S2, the set voltage is 2600 mV; for the ESP32-S3, the set voltage is 2900 mV.

Patch Use Guide

Important

This patch is developed based on ESP-IDF v4.4.8 and v5.3.1. If you need to use this solution with other versions of ESP-IDF, please refer to the patch content and modify ESP-IDF accordingly.

How to Apply a Patch Based on ESP-IDF v4.4.8

Using the ESP32-S3 as an example, please load the patch as follows:

  1. Please make sure ESP-IDF has been checked out to the v4.4.8

  2. Using command git am --signoff < esp32s3_adc_range_to_3300.patch to apply the patch to ESP-IDF

  3. Please note that this solution is only effective for the esp_adc_cal_get_voltage interface. Users can directly call this interface to obtain the extended readings.

How to Apply a Patch Based on ESP-IDF v5.3.1

Using the ESP32-S3 as an example, please load the patch as follows:

  1. Please make sure ESP-IDF has been checked out to the v5.3.1

  2. Using command git am --signoff < esp32s3_adc_range_to_3300_v531.patch to apply the patch to ESP-IDF

  3. Please note that this solution is only effective for the adc_oneshot_get_calibrated_result interface. Users can directly call this interface to obtain the extended readings.

API Guide

The method to obtain the voltage value after ADC range extension varies for different versions of ESP-IDF:

  • ESP-IDF v4.4.8

    1. To get the range expansion result, users must directly use esp_adc_cal_get_voltage to get the voltage of ADC1 or ADC2.

    2. Other APIs of ESP-IDF v4.4.8 ADC are not affected, and the read results are consistent with the default results

  • ESP-IDF v5.3.1

    1. To get the range expansion result, users must directly use adc_oneshot_get_calibrated_result to get the voltage of ADC1 or ADC2.

    2. Other APIs of ESP-IDF v5.3.1 ADC are not affected, and the read results are consistent with the default results

The patch enables ADC range extension by default and uses the float data type for correction. If you need to disable ADC extension or change the data type used during the correction process, please refer to the following procedure:

  • For ESP-IDF v4.4.8: Please use menuconfig to modify the settings under Component config → Driver configurations → ADC configuration → ADC User Code Offset

  • For ESP-IDF v5.3.1: Please use menuconfig to modify the settings under Component config → ADC and ADC Calibration → ADC User Code Offset

Comparison of ADC Range Extension Effects

ESP32-S2 ADC Range Extension Effects Comparison:

../_images/esp32-s2-adc-extension.png

ESP32-S3 ADC Range Extension Effects Comparison:

../_images/esp32-s3-adc-extension.png

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