Analog to Digital Converter¶

Overview¶

The ESP32-S2 integrates two 13-bit SAR (Successive Approximation Register) ADCs supporting a total of 20 measurement channels (analog enabled pins).

The ADC driver API supports ADC1 (10 channels, attached to GPIOs 1 - 10), and ADC2 (10 channels, attached to GPIOs 11 - 20). However, the usage of ADC2 has some restrictions for the application:

Different from ADC1, the hardware arbiter function is added to ADC2, so when using the API of ADC2 to obtain the sampling voltage, you need to judge whether the result is successfully arbitrated.

Configuration and Reading ADC¶

Each ADC unit supports two work modes, ADC-RTC or ADC-DMA mode. ADC-RTC is controlled by the RTC controller and is suitable for low-frequency sampling operations. ADC-DMA is controlled by a digital controller and is suitable for high-frequency continuous sampling actions.

ADC-RTC mode¶

The ADC should be configured before reading is taken.

For ADC1, configure desired precision and attenuation by calling functions adc1_config_width() and adc1_config_channel_atten().

For ADC2, configure the attenuation by adc2_config_channel_atten(). The reading width of ADC2 is configured every time you take the reading.

Attenuation configuration is done per channel, see adc1_channel_t and adc2_channel_t, set as a parameter of above functions.

Then it is possible to read ADC conversion result with adc1_get_raw() and adc2_get_raw(). Reading width of ADC2 should be set as a parameter of adc2_get_raw() instead of in the configuration functions.

Note

Since the ADC2 is shared with the WIFI module, which has higher priority, reading operation of adc2_get_raw() will fail between esp_wifi_start() and esp_wifi_stop(). Use the return code to see whether the reading is successful.

This API provides convenient way to configure ADC1 for reading from ULP. To do so, call function adc1_ulp_enable() and then set precision and attenuation as discussed above.

There is another specific function adc_vref_to_gpio() used to route internal reference voltage to a GPIO pin. It comes handy to calibrate ADC reading and this is discussed in section Minimizing Noise.

Application Examples¶

Reading voltage on ADC1 channel 0 (GPIO 0):

#include <driver/adc.h>

...

    adc1_config_width(ADC_WIDTH_BIT_12);
    adc1_config_channel_atten(ADC1_CHANNEL_0,ADC_ATTEN_DB_0);
    int val = adc1_get_raw(ADC1_CHANNEL_0);

The input voltage in above example is from 0 to 1.1V (0 dB attenuation). The input range can be extended by setting higher attenuation, see adc_atten_t. An example using the ADC driver including calibration (discussed below) is available in esp-idf: peripherals/adc

Reading voltage on ADC2 channel 7 (GPIO 0):

#include <driver/adc.h>

...

    int read_raw;
    adc2_config_channel_atten( ADC2_CHANNEL_7, ADC_ATTEN_0db );

    esp_err_t r = adc2_get_raw( ADC2_CHANNEL_7, ADC_WIDTH_12Bit, &read_raw);
    if ( r == ESP_OK ) {
        printf("%d\n", read_raw );
    } else if ( r == ESP_ERR_TIMEOUT ) {
        printf("ADC2 used by Wi-Fi.\n");
    }

The reading may fail due to collision with Wi-Fi, should check it. An example using the ADC2 driver to read the output of DAC is available in esp-idf: peripherals/adc2

The value read in both these examples is 13 bits wide (range 0-8191).

Minimizing Noise¶

The ESP32-S2 ADC can be sensitive to noise leading to large discrepancies in ADC readings. To minimize noise, users may connect a 0.1uF capacitor to the ADC input pad in use. Multisampling may also be used to further mitigate the effects of noise.

Graph illustrating noise mitigation using capacitor and multisampling of 64 samples.¶

ADC Calibration¶

The esp_adc_cal/include/esp_adc_cal.h API provides functions to correct for differences in measured voltages caused by variation of ADC reference voltages (Vref) between chips. Per design the ADC reference voltage is 1100mV, however the true reference voltage can range from 1000mV to 1200mV amongst different ESP32-S2s.

Graph illustrating effect of differing reference voltages on the ADC voltage curve.¶

Correcting ADC readings using this API involves characterizing one of the ADCs at a given attenuation to obtain a characteristics curve (ADC-Voltage curve) that takes into account the difference in ADC reference voltage. The characteristics curve is in the form of y = coeff_a * x + coeff_b and is used to convert ADC readings to voltages in mV. Calculation of the characteristics curve is based on calibration values which can be stored in eFuse or provided by the user.

Calibration Values¶

Calibration values are used to generate characteristic curves that account for the unique ADC reference voltage of a particular ESP32-S2. There are currently three sources of calibration values. The availability of these calibration values will depend on the type and production date of the ESP32-S2 chip/module.

Two Point values represent each of the ADCs’ readings at 150mV and 850mV. To obtain more accurate calibration results these values should be measured by user and burned into eFuse BLOCK3.
eFuse Vref represents the true ADC reference voltage. This value is measured and burned into eFuse BLOCK0 during factory calibration.
Default Vref is an estimate of the ADC reference voltage provided by the user as a parameter during characterization. If Two Point or eFuse Vref values are unavailable, Default Vref will be used.

Application Example¶

For a full example see esp-idf: peripherals/adc

Characterizing an ADC at a particular attenuation:

#include "driver/adc.h"
#include "esp_adc_cal.h"

...

    //Characterize ADC at particular atten
    esp_adc_cal_characteristics_t *adc_chars = calloc(1, sizeof(esp_adc_cal_characteristics_t));
    esp_adc_cal_value_t val_type = esp_adc_cal_characterize(unit, atten, ADC_WIDTH_BIT_12, DEFAULT_VREF, adc_chars);
    //Check type of calibration value used to characterize ADC
    if (val_type == ESP_ADC_CAL_VAL_EFUSE_VREF) {
        printf("eFuse Vref");
    } else if (val_type == ESP_ADC_CAL_VAL_EFUSE_TP) {
        printf("Two Point");
    } else {
        printf("Default");
    }

Reading an ADC then converting the reading to a voltage:

#include "driver/adc.h"
#include "esp_adc_cal.h"

...
    uint32_t reading =  adc1_get_raw(ADC1_CHANNEL_5);
    uint32_t voltage = esp_adc_cal_raw_to_voltage(reading, adc_chars);

Routing ADC reference voltage to GPIO, so it can be manually measured (for Default Vref):

#include "driver/adc.h"

...

    esp_err_t status = adc_vref_to_gpio(ADC_UNIT_1, GPIO_NUM_25);
    if (status == ESP_OK) {
        printf("v_ref routed to GPIO\n");
    } else {
        printf("failed to route v_ref\n");
    }

GPIO Lookup Macros¶

There are macros available to specify the GPIO number of a ADC channel, or vice versa. e.g.

ADC1_CHANNEL_0_GPIO_NUM is the GPIO number of ADC1 channel 0 (36);
ADC1_GPIO32_CHANNEL is the ADC1 channel number of GPIO 32 (ADC1 channel 4).

API Reference¶

This reference covers three components:

ADC driver
ADC Calibration
GPIO Lookup Macros

ADC driver¶

Header File¶

driver/esp32s2/include/driver/adc.h

Functions¶

esp_err_t adc_arbiter_config(adc_unit_t adc_unit, adc_arbiter_t *config)¶

Config ADC module arbiter. The arbiter is to improve the use efficiency of ADC2. After the control right is robbed by the high priority, the low priority controller will read the invalid ADC2 data, and the validity of the data can be judged by the flag bit in the data.

Note

Only ADC2 support arbiter.

Note

Default priority: Wi-Fi > RTC > Digital;

Note

In normal use, there is no need to call this interface to config arbiter.

Return

ESP_OK Success
ESP_ERR_NOT_SUPPORTED ADC unit not support arbiter.

Parameters

adc_unit: ADC unit.
config: Refer to adc_arbiter_t.

esp_err_t adc_digi_init(void)¶

ADC digital controller initialization.

Return

ESP_OK Success

esp_err_t adc_digi_deinit(void)¶

ADC digital controller deinitialization.

Return

ESP_OK Success

esp_err_t adc_digi_controller_config(const adc_digi_config_t *config)¶

Setting the digital controller.

Return

ESP_OK Success

Parameters

config: Pointer to digital controller paramter. Refer to adc_digi_config_t.

esp_err_t adc_digi_start(void)¶

Enable digital controller to trigger the measurement.

Return

ESP_OK Success

esp_err_t adc_digi_stop(void)¶

Disable digital controller to trigger the measurement.

Return

ESP_OK Success

esp_err_t adc_digi_filter_reset(adc_digi_filter_idx_t idx)¶

Reset adc digital controller filter.

Return

ESP_OK Success

Parameters

idx: Filter index.

esp_err_t adc_digi_filter_set_config(adc_digi_filter_idx_t idx, adc_digi_filter_t *config)¶

Set adc digital controller filter configuration.

Note

For ESP32S2, Filter IDX0/IDX1 can only be used to filter all enabled channels of ADC1/ADC2 unit at the same time.

Return

ESP_OK Success

Parameters

idx: Filter index.
config: See adc_digi_filter_t.

esp_err_t adc_digi_filter_get_config(adc_digi_filter_idx_t idx, adc_digi_filter_t *config)¶

Get adc digital controller filter configuration.

Note

For ESP32S2, Filter IDX0/IDX1 can only be used to filter all enabled channels of ADC1/ADC2 unit at the same time.

Return

ESP_OK Success

Parameters

idx: Filter index.
config: See adc_digi_filter_t.

esp_err_t adc_digi_filter_enable(adc_digi_filter_idx_t idx, bool enable)¶

Enable/disable adc digital controller filter. Filtering the ADC data to obtain smooth data at higher sampling rates.

Note

For ESP32S2, Filter IDX0/IDX1 can only be used to filter all enabled channels of ADC1/ADC2 unit at the same time.

Return

ESP_OK Success

Parameters

idx: Filter index.
enable: Enable/Disable filter.

esp_err_t adc_digi_monitor_set_config(adc_digi_monitor_idx_t idx, adc_digi_monitor_t *config)¶

Config monitor of adc digital controller.

Note

For ESP32S2, The monitor will monitor all the enabled channel data of the each ADC unit at the same time.

Return

ESP_OK Success

Parameters

idx: Monitor index.
config: See adc_digi_monitor_t.

esp_err_t adc_digi_monitor_enable(adc_digi_monitor_idx_t idx, bool enable)¶

Enable/disable monitor of adc digital controller.

Note

For ESP32S2, The monitor will monitor all the enabled channel data of the each ADC unit at the same time.

Return

ESP_OK Success

Parameters

idx: Monitor index.
enable: True or false enable monitor.

esp_err_t adc_digi_intr_enable(adc_unit_t adc_unit, adc_digi_intr_t intr_mask)¶

Enable interrupt of adc digital controller by bitmask.

Return

ESP_OK Success

Parameters

adc_unit: ADC unit.
intr_mask: Interrupt bitmask. See adc_digi_intr_t.

esp_err_t adc_digi_intr_disable(adc_unit_t adc_unit, adc_digi_intr_t intr_mask)¶

Disable interrupt of adc digital controller by bitmask.

Return

ESP_OK Success

Parameters

adc_unit: ADC unit.
intr_mask: Interrupt bitmask. See adc_digi_intr_t.

esp_err_t adc_digi_intr_clear(adc_unit_t adc_unit, adc_digi_intr_t intr_mask)¶

Clear interrupt of adc digital controller by bitmask.

Return

ESP_OK Success

Parameters

adc_unit: ADC unit.
intr_mask: Interrupt bitmask. See adc_digi_intr_t.

uint32_t adc_digi_intr_get_status(adc_unit_t adc_unit)¶

Get interrupt status mask of adc digital controller.

Return

intr Interrupt bitmask, See adc_digi_intr_t.

Parameters

adc_unit: ADC unit.

esp_err_t adc_digi_isr_register(void (*fn)(void *), void *arg, int intr_alloc_flags, )¶

Register ADC interrupt handler, the handler is an ISR. The handler will be attached to the same CPU core that this function is running on.

Return

ESP_OK Success
ESP_ERR_NOT_FOUND Can not find the interrupt that matches the flags.
ESP_ERR_INVALID_ARG Function pointer error.

Parameters

fn: Interrupt handler function.
arg: Parameter for handler function
intr_alloc_flags: Flags used to allocate the interrupt. One or multiple (ORred) ESP_INTR_FLAG_* values. See esp_intr_alloc.h for more info.

esp_err_t adc_digi_isr_deregister(void)¶

Deregister ADC interrupt handler, the handler is an ISR.

Return

ESP_OK Success
ESP_ERR_INVALID_ARG hander error.
ESP_FAIL ISR not be registered.

esp_err_t adc_set_i2s_data_source(adc_i2s_source_t src)¶

Set I2S data source.

Parameters

src: I2S DMA data source, I2S DMA can get data from digital signals or from ADC.

Return

ESP_OK success

esp_err_t adc_i2s_mode_init(adc_unit_t adc_unit, adc_channel_t channel)¶

Initialize I2S ADC mode.

Parameters

adc_unit: ADC unit index
channel: ADC channel index

Return

ESP_OK success
ESP_ERR_INVALID_ARG Parameter error

Header File¶

soc/include/hal/adc_types.h

Structures¶

struct adc_digi_output_data_t¶

ADC digital controller (DMA mode) output data format. Used to analyze the acquired ADC (DMA) data.

Note: ESP32S2: Member channel can be used to judge the validity of the ADC data, because the role of the arbiter may get invalid ADC data.

Public Members

uint16_t data : 12¶

ADC real output data info. Resolution: 12 bit.

ADC real output data info. Resolution: 11 bit.

uint16_t channel : 4¶: ADC channel index info. For ESP32S2: If (channel < ADC_CHANNEL_MAX), The data is valid. If (channel > ADC_CHANNEL_MAX), The data is invalid.

struct adc_digi_output_data_t::[anonymous]::[anonymous] type1¶: When the configured output format is 12bit. ADC_DIGI_FORMAT_12BIT

uint16_t unit : 1¶: ADC unit index info. 0: ADC1; 1: ADC2.

struct adc_digi_output_data_t::[anonymous]::[anonymous] type2¶: When the configured output format is 11bit. ADC_DIGI_FORMAT_11BIT

struct adc_digi_clk_t¶

ADC digital controller (DMA mode) clock system setting. Expression: controller_clk = (APLL or APB) / (div_num + div_a / div_b + 1).

Public Members

bool use_apll¶: true: use APLL clock; false: use APB clock.

uint32_t div_num¶: Division factor. Range: 0 ~ 255. Note: When a higher frequency clock is used (the division factor is less than 9), the ADC reading value will be slightly offset.

uint32_t div_b¶: Division factor. Range: 1 ~ 63.

uint32_t div_a¶: Division factor. Range: 0 ~ 63.

struct adc_arbiter_t¶

ADC arbiter work mode and priority setting.

Note: ESP32S2: Only ADC2 support arbiter.

Public Members

adc_arbiter_mode_t mode¶: Refer to adc_arbiter_mode_t. Note: only support ADC2.

uint8_t rtc_pri¶: RTC controller priority. Range: 0 ~ 2.

uint8_t dig_pri¶: Digital controller priority. Range: 0 ~ 2.

uint8_t pwdet_pri¶: Wi-Fi controller priority. Range: 0 ~ 2.

struct adc_digi_pattern_table_t¶

ADC digital controller (DMA mode) conversion rules setting.

Public Members

uint8_t atten : 2¶: ADC sampling voltage attenuation configuration. 0: input voltage * 1; 1: input voltage * 1/1.34; 2: input voltage * 1/2; 3: input voltage * 1/3.6.

uint8_t reserved : 2¶: reserved0

uint8_t channel : 4¶: ADC channel index.

uint8_t val¶: Raw entry value

struct adc_digi_config_t¶

ADC digital controller (DMA mode) configuration parameters.

Example setting: Use ADC1 channel0 to measure voltage, the sampling rate is required to be 1KHz: +——————+—–+—–+—–+ | sample rate | 1KHz | 1KHz | 1KHz | +——————+—–+—–+—–+ | conv_mode | single | both | alter | | adc1_pattern_len | 1 | 1 | 1 | | dig_clk.use_apll | 0 | 0 | 0 | | dig_clk.div_num | 99 | 99 | 99 | | dig_clk.div_b | 0 | 0 | 0 | | dig_clk.div_a | 0 | 0 | 0 | | interval | 400 | 400 | 200 | +——————+—–+—–+—–+ | trigger_meas_freq | 1KHz | 1KHz | 2KHz | +——————+—–+—–+—–+

Explain the relationship between conv_limit_num, dma_eof_num and the number of DMA output: +——————+—–+—–+—–+ | conv_mode | single | both | alter | +——————+—–+—–+—–+ | trigger meas times | 1 | 1 | 1 | +——————+—–+—–+—–+ | conv_limit_num | +1 | +1 | +1 | | dma_eof_num | +1 | +2 | +1 | | dma output (byte) | +2 | +4 | +2 | +——————+—–+—–+—–+

Public Members

bool conv_limit_en¶: Enable the function of limiting ADC conversion times. If the number of ADC conversion trigger count is equal to the limit_num, the conversion is stopped.

uint32_t conv_limit_num¶: Set the upper limit of the number of ADC conversion triggers. Range: 1 ~ 255.

uint32_t adc1_pattern_len¶: Pattern table length for digital controller. Range: 0 ~ 16 (0: Don’t change the pattern table setting). The pattern table that defines the conversion rules for each SAR ADC. Each table has 16 items, in which channel selection, resolution and attenuation are stored. When the conversion is started, the controller reads conversion rules from the pattern table one by one. For each controller the scan sequence has at most 16 different rules before repeating itself.

uint32_t adc2_pattern_len¶: Refer to adc1_pattern_len

adc_digi_pattern_table_t *adc1_pattern¶: Pointer to pattern table for digital controller. The table size defined by adc1_pattern_len.

adc_digi_pattern_table_t *adc2_pattern¶: Refer to adc1_pattern

adc_digi_convert_mode_t conv_mode¶: ADC conversion mode for digital controller. See adc_digi_convert_mode_t.

adc_digi_output_format_t format¶: ADC output data format for digital controller. See adc_digi_output_format_t.

uint32_t interval¶: The number of interval clock cycles for the digital controller to trigger the measurement. The unit is the divided clock. Range: 40 ~ 4095. Expression: trigger_meas_freq = controller_clk / 2 / interval. Refer to adc_digi_clk_t. Note: The sampling rate of each channel is also related to the conversion mode (See adc_digi_convert_mode_t) and pattern table settings.

adc_digi_clk_t dig_clk¶: ADC digital controller clock divider settings. Refer to adc_digi_clk_t

uint32_t dma_eof_num¶: DMA eof num of adc digital controller. If the number of measurements reaches dma_eof_num, then dma_in_suc_eof signal is generated in DMA. Note: The converted data in the DMA in link buffer will be multiple of two bytes.

struct adc_digi_filter_t¶

ADC digital controller (DMA mode) filter configuration.

Note: For ESP32S2, The filter object of the ADC is fixed.
Note: For ESP32S2, The filter object is always all enabled channels.

Public Members

adc_unit_t adc_unit¶: Set adc unit number for filter. For ESP32S2, Filter IDX0/IDX1 can only be used to filter all enabled channels of ADC1/ADC2 unit at the same time.

adc_channel_t channel¶: Set adc channel number for filter. For ESP32S2, it’s always ADC_CHANNEL_MAX

adc_digi_filter_mode_t mode¶: Set adc filter mode for filter. See adc_digi_filter_mode_t.

struct adc_digi_monitor_t¶

ADC digital controller (DMA mode) monitor configuration.

Note: For ESP32S2, The monitor object of the ADC is fixed.
Note: For ESP32S2, The monitor object is always all enabled channels.

Public Members

adc_unit_t adc_unit¶: Set adc unit number for monitor. For ESP32S2, monitor IDX0/IDX1 can only be used to monitor all enabled channels of ADC1/ADC2 unit at the same time.

adc_channel_t channel¶: Set adc channel number for monitor. For ESP32S2, it’s always ADC_CHANNEL_MAX

adc_digi_monitor_mode_t mode¶: Set adc monitor mode. See adc_digi_monitor_mode_t.

uint32_t threshold¶: Set monitor threshold of adc digital controller.

Macros¶

ADC_ARBITER_CONFIG_DEFAULT()¶

ADC arbiter default configuration.

Note: ESP32S2: Only ADC2 support arbiter.

Enumerations¶

enum adc_unit_t¶

ADC units selected handle.

Note: For ADC digital controller(DMA mode), ESP32 don’t support ADC_UNIT_2, ADC_UNIT_BOTH, ADC_UNIT_ALTER.

Values:

ADC_UNIT_1 = 1¶: SAR ADC 1.

ADC_UNIT_2 = 2¶: SAR ADC 2.

ADC_UNIT_BOTH = 3¶: SAR ADC 1 and 2.

ADC_UNIT_ALTER = 7¶: SAR ADC 1 and 2 alternative mode.

ADC_UNIT_MAX¶

enum adc_channel_t¶

ADC channels handle. See adc1_channel_t, adc2_channel_t.

Note: For ESP32 ADC1, don’t support ADC_CHANNEL_8, ADC_CHANNEL_9. See adc1_channel_t.

Values:

ADC_CHANNEL_0 = 0¶: ADC channel

ADC_CHANNEL_1¶: ADC channel

ADC_CHANNEL_2¶: ADC channel

ADC_CHANNEL_3¶: ADC channel

ADC_CHANNEL_4¶: ADC channel

ADC_CHANNEL_5¶: ADC channel

ADC_CHANNEL_6¶: ADC channel

ADC_CHANNEL_7¶: ADC channel

ADC_CHANNEL_8¶: ADC channel

ADC_CHANNEL_9¶: ADC channel

ADC_CHANNEL_MAX¶

enum adc_atten_t¶

ADC attenuation parameter. Different parameters determine the range of the ADC. See adc1_config_channel_atten.

Values:

ADC_ATTEN_DB_0 = 0¶: The input voltage of ADC will be reduced to about 1/1

ADC_ATTEN_DB_2_5 = 1¶: The input voltage of ADC will be reduced to about 1/1.34

ADC_ATTEN_DB_6 = 2¶: The input voltage of ADC will be reduced to about 1/2

ADC_ATTEN_DB_11 = 3¶: The input voltage of ADC will be reduced to about 1/3.6

ADC_ATTEN_MAX¶

enum adc_i2s_source_t¶

ESP32 ADC DMA source selection.

Note: It’s be deprecated in ESP32S2. Beacause ESP32S2 don’t use I2S DMA.

Values:

ADC_I2S_DATA_SRC_IO_SIG = 0¶: I2S data from GPIO matrix signal

ADC_I2S_DATA_SRC_ADC = 1¶: I2S data from ADC

ADC_I2S_DATA_SRC_MAX¶

enum adc_bits_width_t¶

ADC resolution setting option.

Note: For ESP32S2. Only support 13 bit resolution. For ESP32. Don’t support 13 bit resolution.

Values:

ADC_WIDTH_BIT_9 = 0¶: ADC capture width is 9Bit. Only ESP32 is supported.

ADC_WIDTH_BIT_10 = 1¶: ADC capture width is 10Bit. Only ESP32 is supported.

ADC_WIDTH_BIT_11 = 2¶: ADC capture width is 11Bit. Only ESP32 is supported.

ADC_WIDTH_BIT_12 = 3¶: ADC capture width is 12Bit. Only ESP32 is supported.

ADC_WIDTH_BIT_13 = 4¶: ADC capture width is 13Bit. Only ESP32S2 is supported.

ADC_WIDTH_MAX¶

enum adc_digi_output_format_t¶

ADC digital controller (DMA mode) output data format option.

Values:

ADC_DIGI_FORMAT_12BIT¶: ADC to DMA data format, [15:12]-channel, [11: 0]-12 bits ADC data (adc_digi_output_data_t). Note: In single convert mode.

ADC_DIGI_FORMAT_11BIT¶: ADC to DMA data format, [15]-adc unit, [14:11]-channel, [10: 0]-11 bits ADC data (adc_digi_output_data_t). Note: In multi or alter convert mode.

ADC_DIGI_FORMAT_MAX¶

enum adc_arbiter_mode_t¶

ADC arbiter work mode option.

Note: ESP32S2: Only ADC2 support arbiter.

Values:

ADC_ARB_MODE_SHIELD¶: Force shield arbiter, Select the highest priority controller to work.

ADC_ARB_MODE_FIX¶: Fixed priority switch controller mode.

ADC_ARB_MODE_LOOP¶: Loop priority switch controller mode. Each controller has the same priority, and the arbiter will switch to the next controller after the measurement is completed.

enum adc_digi_convert_mode_t¶

ADC digital controller (DMA mode) work mode.

Note: The conversion mode affects the sampling frequency: SINGLE_UNIT_1: When the measurement is triggered, only ADC1 is sampled once. SINGLE_UNIT_2: When the measurement is triggered, only ADC2 is sampled once. BOTH_UNIT : When the measurement is triggered, ADC1 and ADC2 are sampled at the same time. ALTER_UNIT : When the measurement is triggered, ADC1 or ADC2 samples alternately.

Values:

ADC_CONV_SINGLE_UNIT_1 = 1¶: SAR ADC 1.

ADC_CONV_SINGLE_UNIT_2 = 2¶: SAR ADC 2.

ADC_CONV_BOTH_UNIT = 3¶: SAR ADC 1 and 2.

ADC_CONV_ALTER_UNIT = 7¶: SAR ADC 1 and 2 alternative mode.

ADC_CONV_UNIT_MAX¶

enum adc_digi_intr_t¶

ADC digital controller (DMA mode) interrupt type options.

Values:

ADC_DIGI_INTR_MASK_MONITOR = 0x1¶

ADC_DIGI_INTR_MASK_MEAS_DONE = 0x2¶

ADC_DIGI_INTR_MASK_ALL = 0x3¶

enum adc_digi_filter_idx_t¶

ADC digital controller (DMA mode) filter index options.

Note: For ESP32S2, The filter object of the ADC is fixed.

Values:

ADC_DIGI_FILTER_IDX0 = 0¶: The filter index 0. For ESP32S2, It can only be used to filter all enabled channels of ADC1 unit at the same time.

ADC_DIGI_FILTER_IDX1¶: The filter index 1. For ESP32S2, It can only be used to filter all enabled channels of ADC2 unit at the same time.

ADC_DIGI_FILTER_IDX_MAX¶

enum adc_digi_filter_mode_t¶

ADC digital controller (DMA mode) filter type options. Expression: filter_data = (k-1)/k * last_data + new_data / k.

Values:

ADC_DIGI_FILTER_IIR_2 = 0¶: The filter mode is first-order IIR filter. The coefficient is 2.

ADC_DIGI_FILTER_IIR_4¶: The filter mode is first-order IIR filter. The coefficient is 4.

ADC_DIGI_FILTER_IIR_8¶: The filter mode is first-order IIR filter. The coefficient is 8.

ADC_DIGI_FILTER_IIR_16¶: The filter mode is first-order IIR filter. The coefficient is 16.

ADC_DIGI_FILTER_IIR_64¶: The filter mode is first-order IIR filter. The coefficient is 64.

ADC_DIGI_FILTER_IIR_MAX¶

enum adc_digi_monitor_idx_t¶

ADC digital controller (DMA mode) monitor index options.

Note: For ESP32S2, The monitor object of the ADC is fixed.

Values:

ADC_DIGI_MONITOR_IDX0 = 0¶: The monitor index 0. For ESP32S2, It can only be used to monitor all enabled channels of ADC1 unit at the same time.

ADC_DIGI_MONITOR_IDX1¶: The monitor index 1. For ESP32S2, It can only be used to monitor all enabled channels of ADC2 unit at the same time.

ADC_DIGI_MONITOR_IDX_MAX¶

enum adc_digi_monitor_mode_t¶

Set monitor mode of adc digital controller. MONITOR_HIGH:If ADC_OUT > threshold, Generates monitor interrupt. MONITOR_LOW: If ADC_OUT < threshold, Generates monitor interrupt.

Values:

ADC_DIGI_MONITOR_HIGH = 0¶: If ADC_OUT > threshold, Generates monitor interrupt.

ADC_DIGI_MONITOR_LOW¶: If ADC_OUT < threshold, Generates monitor interrupt.

ADC_DIGI_MONITOR_MAX¶

Header File¶

driver/include/driver/adc_common.h

Functions¶

esp_err_t adc1_pad_get_io_num(adc1_channel_t channel, gpio_num_t *gpio_num)¶

Get the GPIO number of a specific ADC1 channel.

Return

ESP_OK if success
ESP_ERR_INVALID_ARG if channel not valid

Parameters

channel: Channel to get the GPIO number
gpio_num: output buffer to hold the GPIO number

esp_err_t adc1_config_channel_atten(adc1_channel_t channel, adc_atten_t atten)¶

Set the attenuation of a particular channel on ADC1, and configure its associated GPIO pin mux.

The default ADC full-scale voltage is 1.1 V. To read higher voltages (up to the pin maximum voltage, usually 3.3 V) requires setting >0 dB signal attenuation for that ADC channel.

When VDD_A is 3.3 V:

0 dB attenuation (ADC_ATTEN_DB_0) gives full-scale voltage 1.1 V
2.5 dB attenuation (ADC_ATTEN_DB_2_5) gives full-scale voltage 1.5 V
6 dB attenuation (ADC_ATTEN_DB_6) gives full-scale voltage 2.2 V
11 dB attenuation (ADC_ATTEN_DB_11) gives full-scale voltage 3.9 V (see note below)

0 dB attenuation (ADC_ATTEN_DB_0) between 100 and 950 mV
2.5 dB attenuation (ADC_ATTEN_DB_2_5) between 100 and 1250 mV
6 dB attenuation (ADC_ATTEN_DB_6) between 150 to 1750 mV
11 dB attenuation (ADC_ATTEN_DB_11) between 150 to 2450 mV

Note: The full-scale voltage is the voltage corresponding to a maximum reading (depending on ADC1 configured bit width, this value in ESP32 is: 4095 for 12-bits, 2047 for 11-bits, 1023 for 10-bits, 511 for 9 bits. this value in ESP32S2 is: 8191 for 13-bits.)
Note: At 11 dB attenuation the maximum voltage is limited by VDD_A, not the full scale voltage.
Note: For ESP32: Due to ADC characteristics, most accurate results are obtained within the following approximate voltage ranges:

For maximum accuracy, use the ADC calibration APIs and measure voltages within these recommended ranges.

Note

For any given channel, this function must be called before the first time adc1_get_raw() is called for that channel.

Note

This function can be called multiple times to configure multiple ADC channels simultaneously. adc1_get_raw() can then be called for any configured channel.

Return

ESP_OK success
ESP_ERR_INVALID_ARG Parameter error

Parameters

channel: ADC1 channel to configure
atten: Attenuation level

esp_err_t adc1_config_width(adc_bits_width_t width_bit)¶

Configure ADC1 capture width, meanwhile enable output invert for ADC1. The configuration is for all channels of ADC1.

Return

ESP_OK success
ESP_ERR_INVALID_ARG Parameter error

Parameters

width_bit: Bit capture width for ADC1

int adc1_get_raw(adc1_channel_t channel)¶

Take an ADC1 reading from a single channel.

Note

ESP32: When the power switch of SARADC1, SARADC2, HALL sensor and AMP sensor is turned on, the input of GPIO36 and GPIO39 will be pulled down for about 80ns. When enabling power for any of these peripherals, ignore input from GPIO36 and GPIO39. Please refer to section 3.11 of ‘ECO_and_Workarounds_for_Bugs_in_ESP32’ for the description of this issue.

Note

Call adc1_config_width() before the first time this function is called.

Note

For any given channel, adc1_config_channel_atten(channel) must be called before the first time this function is called. Configuring a new channel does not prevent a previously configured channel from being read.

Return

-1: Parameter error
Other: ADC1 channel reading.

Parameters

channel: ADC1 channel to read

void adc_power_on(void)¶: Enable ADC power.

void adc_power_off(void)¶: Power off SAR ADC This function will force power down for ADC.

esp_err_t adc_gpio_init(adc_unit_t adc_unit, adc_channel_t channel)¶

Initialize ADC pad.

Return

ESP_OK success
ESP_ERR_INVALID_ARG Parameter error

Parameters

adc_unit: ADC unit index
channel: ADC channel index

esp_err_t adc_set_data_inv(adc_unit_t adc_unit, bool inv_en)¶

Set ADC data invert.

Return

ESP_OK success
ESP_ERR_INVALID_ARG Parameter error

Parameters

adc_unit: ADC unit index
inv_en: whether enable data invert

esp_err_t adc_set_clk_div(uint8_t clk_div)¶

Set ADC source clock.

Return

ESP_OK success

Parameters

clk_div: ADC clock divider, ADC clock is divided from APB clock

esp_err_t adc_set_data_width(adc_unit_t adc_unit, adc_bits_width_t width_bit)¶

Configure ADC capture width.

Note

For ESP32S2, only support ADC_WIDTH_BIT_13.

Return

ESP_OK success
ESP_ERR_INVALID_ARG Parameter error

Parameters

adc_unit: ADC unit index
width_bit: Bit capture width for ADC unit. For ESP32S2, only support ADC_WIDTH_BIT_13.

void adc1_ulp_enable(void)¶

Configure ADC1 to be usable by the ULP.

This function reconfigures ADC1 to be controlled by the ULP. Effect of this function can be reverted using adc1_get_raw() function.

Note that adc1_config_channel_atten, adc1_config_width() functions need to be called to configure ADC1 channels, before ADC1 is used by the ULP.

esp_err_t adc2_pad_get_io_num(adc2_channel_t channel, gpio_num_t *gpio_num)¶

Get the GPIO number of a specific ADC2 channel.

Return

ESP_OK if success
ESP_ERR_INVALID_ARG if channel not valid

Parameters

channel: Channel to get the GPIO number
gpio_num: output buffer to hold the GPIO number

esp_err_t adc2_config_channel_atten(adc2_channel_t channel, adc_atten_t atten)¶

Configure the ADC2 channel, including setting attenuation.

The default ADC full-scale voltage is 1.1 V. To read higher voltages (up to the pin maximum voltage, usually 3.3 V) requires setting >0 dB signal attenuation for that ADC channel.

When VDD_A is 3.3 V:

0 dB attenuation (ADC_ATTEN_0db) gives full-scale voltage 1.1 V
2.5 dB attenuation (ADC_ATTEN_2_5db) gives full-scale voltage 1.5 V
6 dB attenuation (ADC_ATTEN_6db) gives full-scale voltage 2.2 V
11 dB attenuation (ADC_ATTEN_11db) gives full-scale voltage 3.9 V (see note below)

Note

This function also configures the input GPIO pin mux to connect it to the ADC2 channel. It must be called before calling adc2_get_raw() for this channel.

Note

The full-scale voltage is the voltage corresponding to a maximum reading (depending on ADC2 configured bit width, this value of ESP32 is: 4095 for 12-bits, 2047 for 11-bits, 1023 for 10-bits, 511 for 9 bits. this value of ESP32S2 is: 8191 for 13-bits.)

Note

At 11 dB attenuation the maximum voltage is limited by VDD_A, not the full scale voltage.

Return

ESP_OK success
ESP_ERR_INVALID_ARG Parameter error

Parameters

channel: ADC2 channel to configure
atten: Attenuation level

esp_err_t adc2_get_raw(adc2_channel_t channel, adc_bits_width_t width_bit, int *raw_out)¶

Take an ADC2 reading on a single channel.

Note

ESP32: When the power switch of SARADC1, SARADC2, HALL sensor and AMP sensor is turned on, the input of GPIO36 and GPIO39 will be pulled down for about 80ns. When enabling power for any of these peripherals, ignore input from GPIO36 and GPIO39. Please refer to section 3.11 of ‘ECO_and_Workarounds_for_Bugs_in_ESP32’ for the description of this issue.

Note

ESP32: For a given channel, adc2_config_channel_atten() must be called before the first time this function is called. If Wi-Fi is started via esp_wifi_start(), this function will always fail with ESP_ERR_TIMEOUT.

Note

ESP32S2: ADC2 support hardware arbiter. The arbiter is to improve the use efficiency of ADC2. After the control right is robbed by the high priority, the low priority controller will read the invalid ADC2 data. Default priority: Wi-Fi > RTC > Digital;

Return

ESP_OK if success
ESP_ERR_TIMEOUT ADC2 is being used by other controller and the request timed out.
ESP_ERR_INVALID_STATE The controller status is invalid. Please try again.

Parameters

channel: ADC2 channel to read
width_bit: Bit capture width for ADC2. For ESP32S2, only support ADC_WIDTH_BIT_13.
raw_out: the variable to hold the output data.

esp_err_t adc_vref_to_gpio(adc_unit_t adc_unit, gpio_num_t gpio)¶

Output ADC1 or ADC2’s reference voltage to adc2_channe_t’s IO.

This function routes the internal reference voltage of ADCn to one of ADC2’s channels. This reference voltage can then be manually measured for calibration purposes.

Note

ESP32 only supports output of ADC2’s internal reference voltage.

Return

ESP_OK: v_ref successfully routed to selected GPIO
ESP_ERR_INVALID_ARG: Unsupported GPIO

Parameters

[in] adc_unit: ADC unit index
[in] gpio: GPIO number (Only ADC2’s channels IO are supported)

esp_err_t adc2_vref_to_gpio(gpio_num_t gpio)¶

Output ADC2 reference voltage to adc2_channe_t’s IO.

This function routes the internal reference voltage of ADCn to one of ADC2’s channels. This reference voltage can then be manually measured for calibration purposes.

Return

ESP_OK: v_ref successfully routed to selected GPIO
ESP_ERR_INVALID_ARG: Unsupported GPIO

Parameters

[in] gpio: GPIO number (ADC2’s channels are supported)

Macros¶

ADC_ATTEN_0db¶

ADC rtc controller attenuation option.

Note: This definitions are only for being back-compatible

ADC_ATTEN_2_5db¶

ADC_ATTEN_6db¶

ADC_ATTEN_11db¶

ADC_WIDTH_9Bit¶

ADC_WIDTH_10Bit¶

ADC_WIDTH_11Bit¶

ADC_WIDTH_12Bit¶

Enumerations¶

enum adc1_channel_t¶

Values:

ADC1_CHANNEL_0 = 0¶: ADC1 channel 0 is GPIO36 (ESP32), GPIO1 (ESP32-S2)

ADC1_CHANNEL_1¶: ADC1 channel 1 is GPIO37 (ESP32), GPIO2 (ESP32-S2)

ADC1_CHANNEL_2¶: ADC1 channel 2 is GPIO38 (ESP32), GPIO3 (ESP32-S2)

ADC1_CHANNEL_3¶: ADC1 channel 3 is GPIO39 (ESP32), GPIO4 (ESP32-S2)

ADC1_CHANNEL_4¶: ADC1 channel 4 is GPIO32 (ESP32), GPIO5 (ESP32-S2)

ADC1_CHANNEL_5¶: ADC1 channel 5 is GPIO33 (ESP32), GPIO6 (ESP32-S2)

ADC1_CHANNEL_6¶: ADC1 channel 6 is GPIO34 (ESP32), GPIO7 (ESP32-S2)

ADC1_CHANNEL_7¶: ADC1 channel 7 is GPIO35 (ESP32), GPIO8 (ESP32-S2)

ADC1_CHANNEL_8¶: ADC1 channel 6 is GPIO9 (ESP32-S2)

ADC1_CHANNEL_9¶: ADC1 channel 7 is GPIO10 (ESP32-S2)

ADC1_CHANNEL_MAX¶

enum adc2_channel_t¶

Values:

ADC2_CHANNEL_0 = 0¶: ADC2 channel 0 is GPIO4 (ESP32), GPIO11 (ESP32-S2)

ADC2_CHANNEL_1¶: ADC2 channel 1 is GPIO0 (ESP32), GPIO12 (ESP32-S2)

ADC2_CHANNEL_2¶: ADC2 channel 2 is GPIO2 (ESP32), GPIO13 (ESP32-S2)

ADC2_CHANNEL_3¶: ADC2 channel 3 is GPIO15 (ESP32), GPIO14 (ESP32-S2)

ADC2_CHANNEL_4¶: ADC2 channel 4 is GPIO13 (ESP32), GPIO15 (ESP32-S2)

ADC2_CHANNEL_5¶: ADC2 channel 5 is GPIO12 (ESP32), GPIO16 (ESP32-S2)

ADC2_CHANNEL_6¶: ADC2 channel 6 is GPIO14 (ESP32), GPIO17 (ESP32-S2)

ADC2_CHANNEL_7¶: ADC2 channel 7 is GPIO27 (ESP32), GPIO18 (ESP32-S2)

ADC2_CHANNEL_8¶: ADC2 channel 8 is GPIO25 (ESP32), GPIO19 (ESP32-S2)

ADC2_CHANNEL_9¶: ADC2 channel 9 is GPIO26 (ESP32), GPIO20 (ESP32-S2)

ADC2_CHANNEL_MAX¶

enum adc_i2s_encode_t¶

ADC digital controller encode option.

Values:

ADC_ENCODE_12BIT¶: ADC to DMA data format, , [15:12]-channel [11:0]-12 bits ADC data

ADC_ENCODE_11BIT¶: ADC to DMA data format, [15]-unit, [14:11]-channel [10:0]-11 bits ADC data

ADC_ENCODE_MAX¶

ADC Calibration¶

Header File¶

esp_adc_cal/include/esp_adc_cal.h

Functions¶

esp_err_t esp_adc_cal_check_efuse(esp_adc_cal_value_t value_type)¶

Checks if ADC calibration values are burned into eFuse.

This function checks if ADC reference voltage or Two Point values have been burned to the eFuse of the current ESP32

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 default_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

Two Point values and eFuse Vref can be enabled/disabled using menuconfig.

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 (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_TIMEOUT: Error, timed out attempting to read ADC
ESP_ERR_INVALID_ARG: Error due to invalid arguments

Parameters

[in] channel: ADC Channel to read
[in] chars: Pointer to initialized ADC characteristics structure
[out] voltage: Pointer to store converted voltage

Structures¶

struct esp_adc_cal_characteristics_t¶

Structure storing characteristics of an ADC.

Note: Call esp_adc_cal_characterize() to initialize the structure

Public Members

adc_unit_t adc_num¶: ADC number

adc_atten_t atten¶: ADC attenuation

adc_bits_width_t bit_width¶: ADC bit width

uint32_t coeff_a¶: Gradient of ADC-Voltage curve

uint32_t coeff_b¶: Offset of ADC-Voltage curve

uint32_t vref¶: Vref used by lookup table

const uint32_t *low_curve¶: Pointer to low Vref curve of lookup table (NULL if unused)

const uint32_t *high_curve¶: Pointer to high Vref curve of lookup table (NULL if unused)

Enumerations¶

enum esp_adc_cal_value_t¶

Type of calibration value used in characterization.

Values:

ESP_ADC_CAL_VAL_EFUSE_VREF = 0¶: Characterization based on reference voltage stored in eFuse

ESP_ADC_CAL_VAL_EFUSE_TP = 1¶: Characterization based on Two Point values stored in eFuse

ESP_ADC_CAL_VAL_DEFAULT_VREF = 2¶: Characterization based on default reference voltage

GPIO Lookup Macros¶

Header File¶

soc/soc/esp32/include/soc/adc_channel.h

Macros¶

ADC1_GPIO36_CHANNEL¶

ADC1_CHANNEL_0_GPIO_NUM¶

ADC1_GPIO37_CHANNEL¶

ADC1_CHANNEL_1_GPIO_NUM¶

ADC1_GPIO38_CHANNEL¶

ADC1_CHANNEL_2_GPIO_NUM¶

ADC1_GPIO39_CHANNEL¶

ADC1_CHANNEL_3_GPIO_NUM¶

ADC1_GPIO32_CHANNEL¶

ADC1_CHANNEL_4_GPIO_NUM¶

ADC1_GPIO33_CHANNEL¶

ADC1_CHANNEL_5_GPIO_NUM¶

ADC1_GPIO34_CHANNEL¶

ADC1_CHANNEL_6_GPIO_NUM¶

ADC1_GPIO35_CHANNEL¶

ADC1_CHANNEL_7_GPIO_NUM¶

ADC2_GPIO4_CHANNEL¶

ADC2_CHANNEL_0_GPIO_NUM¶

ADC2_GPIO0_CHANNEL¶

ADC2_CHANNEL_1_GPIO_NUM¶

ADC2_GPIO2_CHANNEL¶

ADC2_CHANNEL_2_GPIO_NUM¶

ADC2_GPIO15_CHANNEL¶

ADC2_CHANNEL_3_GPIO_NUM¶

ADC2_GPIO13_CHANNEL¶

ADC2_CHANNEL_4_GPIO_NUM¶

ADC2_GPIO12_CHANNEL¶

ADC2_CHANNEL_5_GPIO_NUM¶

ADC2_GPIO14_CHANNEL¶

ADC2_CHANNEL_6_GPIO_NUM¶

ADC2_GPIO27_CHANNEL¶

ADC2_CHANNEL_7_GPIO_NUM¶

ADC2_GPIO25_CHANNEL¶

ADC2_CHANNEL_8_GPIO_NUM¶

ADC2_GPIO26_CHANNEL¶

ADC2_CHANNEL_9_GPIO_NUM¶

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