Analog to Digital Converter¶
Overview¶
The ESP32 integrates two 12-bit SAR (Successive Approximation Register) ADCs, supporting a total of 18 measurement channels (analog enabled pins).
These channels are supported:
- ADC1:
8 channels: GPIO32 - GPIO39
- ADC2:
10 channels: GPIO0, GPIO2, GPIO4, GPIO12 - GPIO15, GOIO25 - GPIO27
ADC Limitations¶
注解
Some of the ADC2 pins are used as strapping pins (GPIO 0, 2, 15) thus cannot be used freely. Such is the case in the following official Development Kits:
ESP32 DevKitC: GPIO 0 cannot be used due to external auto program circuits.
ESP-WROVER-KIT: GPIO 0, 2, 4 and 15 cannot be used due to external connections for different purposes.
Since the ADC2 module is also used by the Wi-Fi, only one of them could get the preemption when using together, which means the
adc2_get_raw()
may get blocked until Wi-Fi stops, and vice versa.
Driver Usage¶
Each ADC unit supports two work modes, ADC single read mode and ADC continuous (DMA) mode. ADC single read mode is suitable for low-frequency sampling operations. ADC continuous (DMA) read mode is suitable for high-frequency continuous sampling actions.
注解
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()
andadc1_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.
It is also possible to read the internal hall effect sensor via ADC1 by calling dedicated function hall_sensor_read()
. Note that even the hall sensor is internal to ESP32, reading from it uses channels 0 and 3 of ADC1 (GPIO 36 and 39). Do not connect anything else to these pins and do not change their configuration. Otherwise it may affect the measurement of low value signal from the sensor.
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.
注解
See ADC Limitations for the limitation of using ADC single read mode.
Application Example¶
Reading voltage on ADC1 channel 0 (GPIO 36):
#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 the above example is from 0 to 1.1 V (0 dB attenuation). The input range can be extended by setting a higher attenuation, see adc_atten_t
.
An example of using the ADC driver including calibration (discussed below) is available at esp-idf: peripherals/adc/single_read/adc
Reading voltage on ADC2 channel 7 (GPIO 27):
#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, if the return value of this API is ESP_ERR_INVALID_STATE
, then the reading result is not valid.
An example using the ADC2 driver to read the output of DAC is available in esp-idf: peripherals/adc/single_read/adc2
Reading the internal hall effect sensor:
#include <driver/adc.h>
...
adc1_config_width(ADC_WIDTH_BIT_12);
int val = hall_sensor_read();
The value read in both these examples is 12 bits wide (range 0-4095).
Minimizing Noise¶
The ESP32 ADC can be sensitive to noise leading to large discrepancies in ADC readings. To minimize noise, users may connect a 0.1 µF capacitor to the ADC input pad in use. 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 ESP32s.
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 chip. There are currently 3 source(s) of calibration values on ESP32. The availability of these calibration values will depend on the type and production date of the ESP32 chip/module.
Two Point values represent each of the ADCs’ readings at 150 mV and 850 mV. 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.
Individual measurement and burning of the eFuse Vref has been applied to ESP32-D0WD and ESP32-D0WDQ6 chips produced on/after the 1st week of 2018. Such chips may be recognized by date codes on/later than 012018 (see Line 4 on figure below).
If you would like to purchase chips or modules with calibration, double check with distributor or Espressif (sales@espressif.com) directly.
If you are unable to check the date code (i.e. the chip may be enclosed inside a canned module, etc.), you can still verify if eFuse Vref 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 board’s port name.A chip that has specific eFuse Vref value programmed (in this case 1093 mV) will be reported as follows:
ADC VRef calibration: 1093 mV
In another example below the eFuse Vref is not programmed:
ADC VRef calibration: None (1100 mV nominal)
For a chip with two point calibration the message will look similar to:
ADC VRef calibration: 1149 mV ADC readings stored in efuse BLK3: ADC1 Low reading (150 mV): 306 ADC1 High reading (850 mV): 3153 ADC2 Low reading (150 mV): 389 ADC2 High reading (850 mV): 3206
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¶
Header File¶
Functions¶
-
esp_err_t
adc_set_i2s_data_source
(adc_i2s_source_t src)¶ Set I2S data source.
- Return
ESP_OK success
- Parameters
src
: I2S DMA data source, I2S DMA can get data from digital signals or from ADC.
-
esp_err_t
adc_i2s_mode_init
(adc_unit_t adc_unit, adc_channel_t channel)¶ Initialize I2S ADC mode.
- Return
ESP_OK success
ESP_ERR_INVALID_ARG Parameter error
- Parameters
adc_unit
: ADC unit indexchannel
: ADC channel index
-
int
hall_sensor_read
(void)¶ Read Hall Sensor.
- Note
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
The Hall Sensor uses channels 0 and 3 of ADC1. Do not configure these channels for use as ADC channels.
- Note
The ADC1 module must be enabled by calling adc1_config_width() before calling hall_sensor_read(). ADC1 should be configured for 12 bit readings, as the hall sensor readings are low values and do not cover the full range of the ADC.
- Return
The hall sensor reading.
Header File¶
Structures¶
-
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. Modification of attenuation affects the range of measurements. 0: measurement range 0 - 800mV, 1: measurement range 0 - 1100mV, 2: measurement range 0 - 1350mV, 3: measurement range 0 - 2600mV.
-
uint8_t
bit_width
: 2¶ ADC resolution.
0: 9 bit;
1: 10 bit;
2: 11 bit;
3: 12 bit.
-
int8_t
channel
: 4¶ ADC channel index.
-
uint8_t
val
¶ Raw data value
-
uint8_t
-
struct
adc_digi_output_data_t
¶ ADC digital controller (DMA mode) output data format. Used to analyze the acquired ADC (DMA) data.
- 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
: 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 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
¶ 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
-
uint16_t
val
¶ Raw data value
-
struct
adc_digi_config_t
¶ CONFIG_IDF_TARGET_ESP32.
ADC digital controller (DMA mode) configuration parameters.
Example setting: When using ADC1 channel0 to measure voltage, the sampling rate is required to be 1 kHz:
+---------------------+--------+--------+--------+ | sample rate | 1 kHz | 1 kHz | 1 kHz | +---------------------+--------+--------+--------+ | 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` | 1 kHz | 1 kHz | 2 kHz | +---------------------+--------+--------+--------+
Explanation of the relationship between
conv_limit_num
,dma_eof_num
and the number of DMA outputs:+---------------------+--------+--------+--------+ | 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
.
-
bool
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:
-
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 use
ADC_CHANNEL_8
,ADC_CHANNEL_9
. Seeadc1_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¶ No input attenumation, ADC can measure up to approx. 800 mV.
-
ADC_ATTEN_DB_2_5
= 1¶ The input voltage of ADC will be attenuated, extending the range of measurement to up to approx. 1100 mV.
-
ADC_ATTEN_DB_6
= 2¶ The input voltage of ADC will be attenuated, extending the range of measurement to up to approx. 1350 mV.
-
ADC_ATTEN_DB_11
= 3¶ The input voltage of ADC will be attenuated, extending the range of measurement to up to approx. 2600 mV.
-
ADC_ATTEN_MAX
¶
-
-
enum
adc_i2s_source_t
¶ ESP32 ADC DMA source selection.
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.
Values:
-
ADC_WIDTH_BIT_9
= 0¶ ADC capture width is 9Bit.
-
ADC_WIDTH_BIT_10
= 1¶ ADC capture width is 10Bit.
-
ADC_WIDTH_BIT_11
= 2¶ ADC capture width is 11Bit.
-
ADC_WIDTH_BIT_12
= 3¶ ADC capture width is 12Bit.
-
ADC_WIDTH_MAX
¶
-
-
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_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: For 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: For multi or alter convert mode.
-
ADC_DIGI_FORMAT_MAX
¶
-
Header File¶
Functions¶
-
void
adc_power_on
(void)¶ Enable ADC power.
-
void
adc_power_off
(void)¶ Power off SAR 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
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 indexchannel
: ADC channel index
-
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 numbergpio_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 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.- Return
ESP_OK success
ESP_ERR_INVALID_ARG Parameter error
- Parameters
channel
: ADC1 channel to configureatten
: 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. 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.
- Return
-1: Parameter error
Other: ADC1 channel reading.
- Parameters
channel
: ADC1 channel to read
-
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 indexinv_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.
- Return
ESP_OK success
ESP_ERR_INVALID_ARG Parameter error
- Parameters
adc_unit
: ADC unit indexwidth_bit
: Bit capture width for ADC unit.
-
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 numbergpio_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 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.- Return
ESP_OK success
ESP_ERR_INVALID_ARG Parameter error
- Parameters
channel
: ADC2 channel to configureatten
: 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. 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 viaesp_wifi_start()
, this function will always fail withESP_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;
- 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 readwidth_bit
: Bit capture width for ADC2raw_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)
-
esp_err_t
adc_digi_controller_config
(const adc_digi_config_t *config)¶ Setting the digital controller.
- Return
ESP_ERR_INVALID_STATE Driver state is invalid.
ESP_ERR_INVALID_ARG If the combination of arguments is invalid.
ESP_OK On success
- Parameters
config
: Pointer to digital controller paramter. Refer toadc_digi_config_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
¶
Enumerations¶
-
enum
adc1_channel_t
¶ Values:
-
ADC1_CHANNEL_0
= 0¶ ADC1 channel 0 is GPIO36
-
ADC1_CHANNEL_1
¶ ADC1 channel 1 is GPIO37
-
ADC1_CHANNEL_2
¶ ADC1 channel 2 is GPIO38
-
ADC1_CHANNEL_3
¶ ADC1 channel 3 is GPIO39
-
ADC1_CHANNEL_4
¶ ADC1 channel 4 is GPIO32
-
ADC1_CHANNEL_5
¶ ADC1 channel 5 is GPIO33
-
ADC1_CHANNEL_6
¶ ADC1 channel 6 is GPIO34
-
ADC1_CHANNEL_7
¶ ADC1 channel 7 is GPIO35
-
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
¶
-
ADC Calibration¶
Header File¶
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.
- 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
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_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
-
ESP_ADC_CAL_VAL_MAX
¶
-
ESP_ADC_CAL_VAL_NOT_SUPPORTED
= ESP_ADC_CAL_VAL_MAX¶
-
GPIO Lookup Macros¶
Header File¶
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
¶