Chapter 2. API Reference
Note in ESP32S2, only ESP_ADC_CAL_VAL_EFUSE_TP is supported. Some old ESP32S2s do not sup-
port this, either. In which case you have to calibrate it manually, possibly by performing your own
two-point calibration on the chip.
Return
• ESP_OK: The calibration mode is supported in eFuse
• ESP_ERR_NOT_SUPPORTED: Error, eFuse values are not burned
• ESP_ERR_INVALID_ARG: Error, invalid argument (ESP_ADC_CAL_VAL_DEFAULT_VREF)
Parameters
• value_type: Type of calibration value (ESP_ADC_CAL_VAL_EFUSE_VREF or
ESP_ADC_CAL_VAL_EFUSE_TP)
esp_adc_cal_value_t esp_adc_cal_characterize(adc_unit_t adc_num, adc_atten_t atten,
adc_bits_width_t bit_width, uint32_t de-
fault_vref, esp_adc_cal_characteristics_t *chars)
Characterize an ADC at a particular attenuation.
This function will characterize the ADC at a particular attenuation and generate the ADC-Voltage curve in the
form of [y = coeff_a * x + coeff_b]. Characterization can be based on Two Point values, eFuse Vref, or default
Vref and the calibration values will be prioritized in that order.
Note For ESP32, Two Point values and eFuse Vref calibration can be enabled/disabled using menuconfig.
For ESP32s2, only Two Point values calibration and only ADC_WIDTH_BIT_13 is supported. The
parameter default_vref is unused.
Return
• ESP_ADC_CAL_VAL_EFUSE_VREF: eFuse Vref used for characterization
• ESP_ADC_CAL_VAL_EFUSE_TP: Two Point value used for characterization (only in Linear
Mode)
• ESP_ADC_CAL_VAL_DEFAULT_VREF: Default Vref used for characterization
Parameters
• [in] adc_num: ADC to characterize (ADC_UNIT_1 or ADC_UNIT_2)
• [in] atten: Attenuation to characterize
• [in] bit_width: Bit width configuration of ADC
• [in] default_vref: Default ADC reference voltage in mV (Only in ESP32, used if eFuse
values is not available)
• [out] chars: Pointer to empty structure used to store ADC characteristics
uint32_t esp_adc_cal_raw_to_voltage(uint32_t adc_reading, const
esp_adc_cal_characteristics_t *chars)
Convert an ADC reading to voltage in mV.
This function converts an ADC reading to a voltage in mV based on the ADC’s characteristics.
Note Characteristics structure must be initialized before this function is called (call
esp_adc_cal_characterize())
Return Voltage in mV
Parameters
• [in] adc_reading: ADC reading
• [in] chars: Pointer to initialized structure containing ADC characteristics
esp_err_t esp_adc_cal_get_voltage(adc_channel_t channel, const esp_adc_cal_characteristics_t
*chars, uint32_t *voltage)
Reads an ADC and converts the reading to a voltage in mV.
This function reads an ADC then converts the raw reading to a voltage in mV based on the characteristics
provided. The ADC that is read is also determined by the characteristics.
Note The Characteristics structure must be initialized before this function is called (call
esp_adc_cal_characterize())
Return
• ESP_OK: ADC read and converted to mV
• ESP_ERR_INVALID_ARG: Error due to invalid arguments
• ESP_ERR_INVALID_STATE: Reading result is invalid. Try to read again.
Parameters
• [in] channel: ADC Channel to read
Espressif Systems 232
Submit Document Feedback
Release v4.4
To Next Page
Loading...
Need help?
General