Analog to Digital Converter (ADC)

ADC Channels

The ESP32-S2 integrates 2 SAR (Successive Approximation Register) ADCs, supporting a total of 20 measurement channels (analog enabled pins).

These channels are supported:

ADC1:

10 channels: GPIO1 - GPIO10

ADC2:

10 channels: GPIO11 - GPIO20

ADC Attenuation

Vref is the reference voltage used internally by ESP32-S2 ADCs for measuring the input voltage. The ESP32-S2 ADCs can measure analog voltages from 0 V to Vref. Among different chips, the Vref varies, the median is 1.1 V. In order to convert voltages larger than Vref, input voltages can be attenuated before being input to the ADCs. There are 4 available attenuation options, the higher the attenuation is, the higher the measurable input voltage could be.

Attenuation	Measurable input voltage range
`ADC_ATTEN_DB_0`	0 mV ~ 750 mV
`ADC_ATTEN_DB_2_5`	0 mV ~ 1050 mV
`ADC_ATTEN_DB_6`	0 mV ~ 1300 mV
`ADC_ATTEN_DB_11`	0 mV ~ 2500 mV

ADC Conversion

An ADC conversion is to convert the input analog voltage to a digital value. The ADC conversion results provided by the ADC driver APIs are raw data. Resolution of ESP32-S2 ADC raw results under Single Read mode is 12-bit.

adc1_get_raw()
adc2_get_raw()

To calculate the voltage based on the ADC raw results, this formula can be used:

Vout = Dout * Vmax / Dmax       (1)

where:

Vout	Digital output result, standing for the voltage.
Dout	ADC raw digital reading result.
Vmax	Maximum measurable input analog voltage, see ADC Attenuation.
Dmax	Maximum of the output ADC raw digital reading result, which is 8191 under Single Read mode, 4095 under Continuous Read mode.

For boards with eFuse ADC calibration bits, esp_adc_cal_raw_to_voltage() can be used to get the calibrated conversion results. These results stand for the actual voltage (in mV). No need to transform these data via the formula (1). If ADC calibration APIs are used on boards without eFuse ADC calibration bits, warnings will be generated. See ADC Calibration.

ADC Limitations

Note

Since the ADC2 module is also used by the Wi-Fi, reading operation of adc2_get_raw() may fail between esp_wifi_start() and esp_wifi_stop(). Use the return code to see whether the reading is successful.

Driver Usage

Both of the ADC units support single read mode, which is suitable for low-frequency sampling operations.

Note

ADC readings from a pin not connected to any signal are random.

ADC Single Read 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.

Single Read mode ADC example can be found in peripherals/adc/single_read directory of ESP-IDF examples.

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 ADC Calibration.

Note

See ADC Limitations for the limitation of using ADC single read mode.

Minimizing Noise

The ESP32-S2 ADC can be sensitive to noise leading to large discrepancies in ADC readings. Depending on the usage scenario, users may connect a bypass capacitor (e.g. a 100 nF ceramic capacitor) to the ADC input pad in use, to minimize noise. Besides, multisampling may also be used to further mitigate the effects of noise.

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 1100 mV, however the true reference voltage can range from 1000 mV to 1200 mV 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 variation of ADC reference voltage of a particular ESP32-S2 chip. There are currently 1 source(s) of calibration values on ESP32-S2. The availability of these calibration values will depend on the type and production date of the ESP32-S2 chip/module.

eFuse Two Point values calibrates the ADC output at two different voltages. This value is measured and burned into eFuse BLOCK0 during factory calibration on newly manufactured ESP32-S2 chips and modules. If you would like to purchase chips or modules with calibration, double check with distributor or Espressif (sales@espressif.com) directly.

You can verify if eFuse Two Point is present by running the espefuse.py tool with adc_info parameter

$IDF_PATH/components/esptool_py/esptool/espefuse.py --port /dev/ttyUSB0 adc_info

Replace /dev/ttyUSB0 with ESP32-S2 board’s port name.

Application Extensions

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

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.
ADC1_GPIOn_CHANNEL is the ADC1 channel number of GPIO n.

API Reference

This reference covers three components:

ADC driver
ADC Calibration
GPIO Lookup Macros

ADC driver

Header File

components/driver/include/driver/adc.h

Functions

void adc_power_on(void)

Enable ADC power.

Deprecated:: Use adc_power_acquire and adc_power_release instead.

void adc_power_off(void)

Power off SAR ADC.

Deprecated:: Use adc_power_acquire and adc_power_release instead. This function will force power down for ADC. This function is deprecated because forcing power ADC power off may disrupt operation of other components which may be using the ADC.

void adc_power_acquire(void): Increment the usage counter for ADC module. ADC will stay powered on while the counter is greater than 0. Call adc_power_release when done using the ADC.

void adc_power_release(void): Decrement the usage counter for ADC module. ADC will stay powered on while the counter is greater than 0. Call this function when done using the ADC.

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.

Parameters

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

Returns

ESP_OK if success
ESP_ERR_INVALID_ARG if channel not valid

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 voltage is for attenuation 0 dB and listed in the table below. By setting higher attenuation it is possible to read higher voltages.

Due to ADC characteristics, most accurate results are obtained within the “suggested range” shown in the following table.

+----------+-------------+-----------------+
|          | attenuation | suggested range |
|    SoC   |     (dB)    |      (mV)       |
+==========+=============+=================+
|          |       0     |    100 ~  950   |
|          +-------------+-----------------+
|          |       2.5   |    100 ~ 1250   |
|   ESP32  +-------------+-----------------+
|          |       6     |    150 ~ 1750   |
|          +-------------+-----------------+
|          |      11     |    150 ~ 2450   |
+----------+-------------+-----------------+
|          |       0     |      0 ~  750   |
|          +-------------+-----------------+
|          |       2.5   |      0 ~ 1050   |
| ESP32-S2 +-------------+-----------------+
|          |       6     |      0 ~ 1300   |
|          +-------------+-----------------+
|          |      11     |      0 ~ 2500   |
+----------+-------------+-----------------+

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. You may call adc1_get_raw() only after configuring a channel.

Parameters

channel – ADC1 channel to configure
atten – Attenuation level

Returns

ESP_OK success
ESP_ERR_INVALID_ARG Parameter error

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.

Parameters

width_bit – Bit capture width for ADC1

Returns

ESP_OK success
ESP_ERR_INVALID_ARG Parameter error

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. As a workaround, call adc_power_acquire() in the app. This will result in higher power consumption (by ~1mA), but will remove the glitches on GPIO36 and GPIO39.

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.

Parameters

channel – ADC1 channel to read

Returns

-1: Parameter error
Other: ADC1 channel reading.

esp_err_t adc_set_data_inv(adc_unit_t adc_unit, bool inv_en)

Set ADC data invert.

Parameters

adc_unit – ADC unit index
inv_en – whether enable data invert

Returns

ESP_OK success
ESP_ERR_INVALID_ARG Parameter error

esp_err_t adc_set_clk_div(uint8_t clk_div)

Set ADC source clock.

Parameters

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

Returns

ESP_OK success

esp_err_t adc_set_data_width(adc_unit_t adc_unit, adc_bits_width_t width_bit)

Configure ADC capture width.

Parameters

adc_unit – ADC unit index
width_bit – Bit capture width for ADC unit.

Returns

ESP_OK success
ESP_ERR_INVALID_ARG Parameter error

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.

Parameters

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

Returns

ESP_OK if success
ESP_ERR_INVALID_ARG if channel not valid

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 voltage is for attenuation 0 dB and listed in the table below. By setting higher attenuation it is possible to read higher voltages.

Due to ADC characteristics, most accurate results are obtained within the “suggested range” shown in the following table.

+----------+-------------+-----------------+
|          | attenuation | suggested range |
|    SoC   |     (dB)    |      (mV)       |
+==========+=============+=================+
|          |       0     |    100 ~  950   |
|          +-------------+-----------------+
|          |       2.5   |    100 ~ 1250   |
|   ESP32  +-------------+-----------------+
|          |       6     |    150 ~ 1750   |
|          +-------------+-----------------+
|          |      11     |    150 ~ 2450   |
+----------+-------------+-----------------+
|          |       0     |      0 ~  750   |
|          +-------------+-----------------+
|          |       2.5   |      0 ~ 1050   |
| ESP32-S2 +-------------+-----------------+
|          |       6     |      0 ~ 1300   |
|          +-------------+-----------------+
|          |      11     |      0 ~ 2500   |
+----------+-------------+-----------------+

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

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

For any given channel, this function must be called before the first time adc2_get_raw() is called for that channel.

Parameters

channel – ADC2 channel to configure
atten – Attenuation level

Returns

ESP_OK success
ESP_ERR_INVALID_ARG Parameter error

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. As a workaround, call adc_power_acquire() in the app. This will result in higher power consumption (by ~1mA), but will remove the glitches on GPIO36 and GPIO39.

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

ESP32-S2: 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;

Parameters

channel – ADC2 channel to read
width_bit – Bit capture width for ADC2
raw_out – the variable to hold the output data.

Returns

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.

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.

Parameters

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

Returns

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

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.

Deprecated:: Use adc_vref_to_gpio instead.

Parameters

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

Returns

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

esp_err_t adc_digi_initialize(const adc_digi_init_config_t *init_config)

Initialize the Digital ADC.

Parameters

init_config – Pointer to Digital ADC initilization config. Refer to adc_digi_init_config_t.

Returns

ESP_ERR_INVALID_ARG If the combination of arguments is invalid.
ESP_ERR_NOT_FOUND No free interrupt found with the specified flags
ESP_ERR_NO_MEM If out of memory
ESP_OK On success

esp_err_t adc_digi_read_bytes(uint8_t *buf, uint32_t length_max, uint32_t *out_length, uint32_t timeout_ms)

Read bytes from Digital ADC through DMA.

Parameters

buf – [out] Buffer to read from ADC.
length_max – [in] Expected length of data read from the ADC.
out_length – [out] Real length of data read from the ADC via this API.
timeout_ms – [in] Time to wait for data via this API, in millisecond.

Returns

ESP_ERR_INVALID_STATE Driver state is invalid. Usually it means the ADC sampling rate is faster than the task processing rate.
ESP_ERR_TIMEOUT Operation timed out
ESP_OK On success

esp_err_t adc_digi_start(void)

Start the Digital ADC and DMA peripherals. After this, the hardware starts working.

Returns

ESP_ERR_INVALID_STATE Driver state is invalid.
ESP_OK On success

esp_err_t adc_digi_stop(void)

Stop the Digital ADC and DMA peripherals. After this, the hardware stops working.

Returns

ESP_ERR_INVALID_STATE Driver state is invalid.
ESP_OK On success

esp_err_t adc_digi_deinitialize(void)

Deinitialize the Digital ADC.

Returns

ESP_ERR_INVALID_STATE Driver state is invalid.
ESP_OK On success

esp_err_t adc_digi_controller_configure(const adc_digi_configuration_t *config)

Setting the digital controller.

Parameters

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

Returns

ESP_ERR_INVALID_STATE Driver state is invalid.
ESP_ERR_INVALID_ARG If the combination of arguments is invalid.
ESP_OK On success

esp_err_t adc_digi_filter_reset(adc_digi_filter_idx_t idx)

Reset adc digital controller filter.

Parameters

idx – Filter index.

Returns

ESP_OK Success

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.

Parameters

idx – Filter index.
config – See adc_digi_filter_t.

Returns

ESP_OK Success

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.

Parameters

idx – Filter index.
config – See adc_digi_filter_t.

Returns

ESP_OK Success

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.

Parameters

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

Returns

ESP_OK Success

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.

Parameters

idx – Monitor index.
config – See adc_digi_monitor_t.

Returns

ESP_OK Success

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.

Parameters

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

Returns

ESP_OK Success

Structures

struct adc_digi_init_config_s

ADC DMA driver configuration.

Public Members

uint32_t max_store_buf_size: Max length of the converted data that driver can store before they are processed.

uint32_t conv_num_each_intr: Bytes of data that can be converted in 1 interrupt.

uint32_t adc1_chan_mask: Channel list of ADC1 to be initialized.

uint32_t adc2_chan_mask: Channel list of ADC2 to be initialized.

struct adc_digi_configuration_t

ADC digital controller settings.

Public Members

bool conv_limit_en: To limit ADC conversion times. Conversion stops after finishing conv_limit_num times conversion.

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

uint32_t pattern_num: Number of ADC channels that will be used.

adc_digi_pattern_config_t *adc_pattern: List of configs for each ADC channel that will be used.

uint32_t sample_freq_hz: The expected ADC sampling frequency in Hz. Range: 611Hz ~ 83333Hz Fs = Fd / interval / 2 Fs: sampling frequency; Fd: digital controller frequency, no larger than 5M for better performance interval: interval between 2 measurement trigger signal, the smallest interval should not be smaller than the ADC measurement period, the largest interval should not be larger than 4095

adc_digi_convert_mode_t conv_mode: ADC DMA conversion mode, see adc_digi_convert_mode_t.

adc_digi_output_format_t format: ADC DMA conversion output format, see adc_digi_output_format_t.

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_BIT_DEFAULT: The default (max) bit width of the ADC of current version. You can also get the maximum bitwidth by SOC_ADC_MAX_BITWIDTH defined in soc_caps.h.

ADC_WIDTH_9Bit

ADC_WIDTH_10Bit

ADC_WIDTH_11Bit

ADC_WIDTH_12Bit

ADC_MAX_DELAY: Digital ADC DMA read max timeout value, it may make the adc_digi_read_bytes block forever if the OS supports.

Type Definitions

typedef struct adc_digi_init_config_s adc_digi_init_config_t: ADC DMA driver configuration.

Enumerations

enum adc1_channel_t

Values:

enumerator ADC1_CHANNEL_0: ADC1 channel 0 is GPIO1

enumerator ADC1_CHANNEL_1: ADC1 channel 1 is GPIO2

enumerator ADC1_CHANNEL_2: ADC1 channel 2 is GPIO3

enumerator ADC1_CHANNEL_3: ADC1 channel 3 is GPIO4

enumerator ADC1_CHANNEL_4: ADC1 channel 4 is GPIO5

enumerator ADC1_CHANNEL_5: ADC1 channel 5 is GPIO6

enumerator ADC1_CHANNEL_6: ADC1 channel 6 is GPIO7

enumerator ADC1_CHANNEL_7: ADC1 channel 7 is GPIO8

enumerator ADC1_CHANNEL_8: ADC1 channel 8 is GPIO9

enumerator ADC1_CHANNEL_9: ADC1 channel 9 is GPIO10

enumerator ADC1_CHANNEL_MAX

enum adc2_channel_t

Values:

enumerator ADC2_CHANNEL_0: ADC2 channel 0 is GPIO4 (ESP32), GPIO11 (ESP32-S2)

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

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

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

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

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

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

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

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

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

enumerator ADC2_CHANNEL_MAX

enum adc_i2s_encode_t

ADC digital controller encode option.

Deprecated:: The ESP32-S2 doesn’t use I2S DMA. Call adc_digi_output_format_t instead.

Values:

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

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

enumerator ADC_ENCODE_MAX

Header File

components/hal/include/hal/adc_types.h

Structures

struct adc_digi_pattern_config_t

ADC digital controller pattern configuration.

Public Members

uint8_t atten: Attenuation of this ADC channel.

uint8_t channel: ADC channel.

uint8_t unit: ADC unit.

uint8_t bit_width: ADC output bit width.

struct adc_digi_output_data_t

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

Note

ESP32: Only type1 is valid. ADC2 does not support DMA mode.

Note

ESP32-S2: 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

ADC real output data info. Resolution: 12 bit.

ADC real output data info. Resolution: 11 bit.

uint16_t channel

ADC channel index info.

ADC channel index info. For ESP32-S2: 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: ADC type1

uint16_t unit: 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

uint16_t val: Raw data value

struct adc_arbiter_t

ADC arbiter work mode and priority setting.

Note

ESP32-S2: 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_filter_t

ADC digital controller (DMA mode) filter configuration.

Note

For ESP32-S2, The filter object of the ADC is fixed.

Note

For ESP32-S2, The filter object is always all enabled channels.

Public Members

adc_unit_t adc_unit: Set adc unit number for filter. For ESP32-S2, 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 ESP32-S2, 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 ESP32-S2, The monitor object of the ADC is fixed.

Note

For ESP32-S2, The monitor object is always all enabled channels.

Public Members

adc_unit_t adc_unit: Set adc unit number for monitor. For ESP32-S2, 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 ESP32-S2, 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.

struct adc_digi_clk_t

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

Note

: The clocks of the DAC digital controller use the ADC digital controller clock divider.

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.

Macros

ADC_ARBITER_CONFIG_DEFAULT(): ADC arbiter default configuration.

Note

ESP32S2: Only ADC2 supports (needs) an arbiter.

Enumerations

enum adc_unit_t

ADC unit enumeration.

Note

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

Values:

enumerator ADC_UNIT_1: SAR ADC 1.

enumerator ADC_UNIT_2: SAR ADC 2.

enumerator ADC_UNIT_BOTH: SAR ADC 1 and 2.

enumerator ADC_UNIT_ALTER: SAR ADC 1 and 2 alternative mode.

enumerator ADC_UNIT_MAX

enum adc_channel_t

ADC channels handle. See adc1_channel_t, adc2_channel_t.

Note

For ESP32 ADC1, don’t use ADC_CHANNEL_8, ADC_CHANNEL_9. See adc1_channel_t.

Values:

enumerator ADC_CHANNEL_0: ADC channel

enumerator ADC_CHANNEL_1: ADC channel

enumerator ADC_CHANNEL_2: ADC channel

enumerator ADC_CHANNEL_3: ADC channel

enumerator ADC_CHANNEL_4: ADC channel

enumerator ADC_CHANNEL_5: ADC channel

enumerator ADC_CHANNEL_6: ADC channel

enumerator ADC_CHANNEL_7: ADC channel

enumerator ADC_CHANNEL_8: ADC channel

enumerator ADC_CHANNEL_9: ADC channel

enumerator ADC_CHANNEL_MAX

enum adc_atten_t

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

Values:

enumerator ADC_ATTEN_DB_0: No input attenumation, ADC can measure up to approx. 800 mV.

enumerator ADC_ATTEN_DB_2_5: The input voltage of ADC will be attenuated extending the range of measurement by about 2.5 dB (1.33 x)

enumerator ADC_ATTEN_DB_6: The input voltage of ADC will be attenuated extending the range of measurement by about 6 dB (2 x)

enumerator ADC_ATTEN_DB_11: The input voltage of ADC will be attenuated extending the range of measurement by about 11 dB (3.55 x)

enumerator ADC_ATTEN_MAX

enum adc_bits_width_t

ADC resolution setting option.

Note

Only used in single read mode

Values:

enumerator ADC_WIDTH_BIT_13: ADC capture width is 13Bit.

enumerator ADC_WIDTH_MAX

enum adc_digi_convert_mode_t

ADC digital controller (DMA mode) work mode.

Values:

enumerator ADC_CONV_SINGLE_UNIT_1: Only use ADC1 for conversion.

enumerator ADC_CONV_SINGLE_UNIT_2: Only use ADC2 for conversion.

enumerator ADC_CONV_BOTH_UNIT: Use Both ADC1 and ADC2 for conversion simultaneously.

enumerator ADC_CONV_ALTER_UNIT: Use both ADC1 and ADC2 for conversion by turn. e.g. ADC1 -> ADC2 -> ADC1 -> ADC2 …..

enumerator ADC_CONV_UNIT_MAX

enum adc_digi_output_format_t

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

Values:

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

enumerator 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: For multi or alter convert mode.

enumerator ADC_DIGI_FORMAT_MAX

enumerator ADC_DIGI_OUTPUT_FORMAT_TYPE1: See adc_digi_output_data_t.type1

enumerator ADC_DIGI_OUTPUT_FORMAT_TYPE2: See adc_digi_output_data_t.type2

enum adc_arbiter_mode_t

ADC arbiter work mode option.

Note

ESP32-S2: Only ADC2 support arbiter.

Values:

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

enumerator ADC_ARB_MODE_FIX: Fixed priority switch controller mode.

enumerator 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_filter_idx_t

ADC digital controller (DMA mode) filter index options.

Note

For ESP32-S2, The filter object of the ADC is fixed.

Values:

enumerator ADC_DIGI_FILTER_IDX0: The filter index 0. For ESP32-S2, It can only be used to filter all enabled channels of ADC1 unit at the same time.

enumerator ADC_DIGI_FILTER_IDX1: The filter index 1. For ESP32-S2, It can only be used to filter all enabled channels of ADC2 unit at the same time.

enumerator 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:

enumerator ADC_DIGI_FILTER_IIR_2: The filter mode is first-order IIR filter. The coefficient is 2.

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

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

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

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

enumerator ADC_DIGI_FILTER_IIR_MAX

enum adc_digi_monitor_idx_t

ADC digital controller (DMA mode) monitor index options.

Note

For ESP32-S2, The monitor object of the ADC is fixed.

Values:

enumerator ADC_DIGI_MONITOR_IDX0: The monitor index 0. For ESP32-S2, It can only be used to monitor all enabled channels of ADC1 unit at the same time.

enumerator ADC_DIGI_MONITOR_IDX1: The monitor index 1. For ESP32-S2, It can only be used to monitor all enabled channels of ADC2 unit at the same time.

enumerator 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:

enumerator ADC_DIGI_MONITOR_HIGH: If ADC_OUT > threshold, Generates monitor interrupt.

enumerator ADC_DIGI_MONITOR_LOW: If ADC_OUT < threshold, Generates monitor interrupt.

enumerator ADC_DIGI_MONITOR_MAX

enum adc_i2s_source_t

ESP32 ADC DMA source selection.

Deprecated:: Not applicable on ESP32-S2 because ESP32-S2 doesn’t use I2S DMA.

Values:

enumerator ADC_I2S_DATA_SRC_IO_SIG: I2S data from GPIO matrix signal

enumerator ADC_I2S_DATA_SRC_ADC: I2S data from ADC

enumerator ADC_I2S_DATA_SRC_MAX

ADC Calibration

Header File

components/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

Note

in ESP32S2, only ESP_ADC_CAL_VAL_EFUSE_TP is supported. Some old ESP32S2s do not support this, either. In which case you have to calibrate it manually, possibly by performing your own two-point calibration on the chip.

Parameters

value_type – Type of calibration value (ESP_ADC_CAL_VAL_EFUSE_VREF or ESP_ADC_CAL_VAL_EFUSE_TP)

Returns

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)

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

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.

Parameters

adc_num – [in] ADC to characterize (ADC_UNIT_1 or ADC_UNIT_2)
atten – [in] Attenuation to characterize
bit_width – [in] Bit width configuration of ADC
default_vref – [in] Default ADC reference voltage in mV (Only in ESP32, used if eFuse values is not available)
chars – [out] Pointer to empty structure used to store ADC characteristics

Returns

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

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())

Parameters

adc_reading – [in] ADC reading
chars – [in] Pointer to initialized structure containing ADC characteristics

Returns

Voltage in mV

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())

Parameters

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

Returns

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.

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)

uint8_t version: ADC Calibration

Enumerations

enum esp_adc_cal_value_t

Type of calibration value used in characterization.

Values:

enumerator ESP_ADC_CAL_VAL_EFUSE_VREF: Characterization based on reference voltage stored in eFuse

enumerator ESP_ADC_CAL_VAL_EFUSE_TP: Characterization based on Two Point values stored in eFuse

enumerator ESP_ADC_CAL_VAL_DEFAULT_VREF: Characterization based on default reference voltage

enumerator ESP_ADC_CAL_VAL_EFUSE_TP_FIT: Characterization based on Two Point values and fitting curve coefficients stored in eFuse

enumerator ESP_ADC_CAL_VAL_MAX

enumerator ESP_ADC_CAL_VAL_NOT_SUPPORTED

GPIO Lookup Macros

Header File

components/soc/esp32s2/include/soc/adc_channel.h

Macros

ADC1_GPIO1_CHANNEL

ADC1_CHANNEL_0_GPIO_NUM

ADC1_GPIO2_CHANNEL

ADC1_CHANNEL_1_GPIO_NUM

ADC1_GPIO3_CHANNEL

ADC1_CHANNEL_2_GPIO_NUM

ADC1_GPIO4_CHANNEL

ADC1_CHANNEL_3_GPIO_NUM

ADC1_GPIO5_CHANNEL

ADC1_CHANNEL_4_GPIO_NUM

ADC1_GPIO6_CHANNEL

ADC1_CHANNEL_5_GPIO_NUM

ADC1_GPIO7_CHANNEL

ADC1_CHANNEL_6_GPIO_NUM

ADC1_GPIO8_CHANNEL

ADC1_CHANNEL_7_GPIO_NUM

ADC1_GPIO9_CHANNEL

ADC1_CHANNEL_8_GPIO_NUM

ADC1_GPIO10_CHANNEL

ADC1_CHANNEL_9_GPIO_NUM

ADC2_GPIO11_CHANNEL

ADC2_CHANNEL_0_GPIO_NUM

ADC2_GPIO12_CHANNEL

ADC2_CHANNEL_1_GPIO_NUM

ADC2_GPIO13_CHANNEL

ADC2_CHANNEL_2_GPIO_NUM

ADC2_GPIO14_CHANNEL

ADC2_CHANNEL_3_GPIO_NUM

ADC2_GPIO15_CHANNEL

ADC2_CHANNEL_4_GPIO_NUM

ADC2_GPIO16_CHANNEL

ADC2_CHANNEL_5_GPIO_NUM

ADC2_GPIO17_CHANNEL

ADC2_CHANNEL_6_GPIO_NUM

ADC2_GPIO18_CHANNEL

ADC2_CHANNEL_7_GPIO_NUM

ADC2_GPIO19_CHANNEL

ADC2_CHANNEL_8_GPIO_NUM

ADC2_GPIO20_CHANNEL

ADC2_CHANNEL_9_GPIO_NUM

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