Analog to Digital Converter (ADC)

{IDF_TARGET_ADC1_CH0: default="GPIO 0", esp32="GPIO 36"} {IDF_TARGET_ADC2_CH7: default="GPIO 0", esp32="GPIO 27"}

Overview

{IDF_TARGET_ADC_DATA_WIDTH:default="12", esp32s2="13"} {IDF_TARGET_ADC_TOTAL_CHAN:default="20", esp32="18", esp32s2="20", esp32c3="6"}

The {IDF_TARGET_NAME} integrates two {IDF_TARGET_ADC_DATA_WIDTH}-bit SAR (Successive Approximation Register) ADCs, supporting a total of {IDF_TARGET_ADC_TOTAL_CHAN} measurement channels (analog enabled pins).

These channels are supported:

esp32

ADC1:

8 channels: GPIO32 - GPIO39

ADC2:

10 channels: GPIO0, GPIO2, GPIO4, GPIO12 - GPIO15, GOIO25 - GPIO27

esp32s2

ADC1:

10 channels: GPIO1 - GPIO10

ADC2:

10 channels: GPIO11 - GPIO20

esp32c3

ADC1:

5 channels: GPIO0 - GPIO4

ADC2:

1 channels: GPIO5

ADC Limitations

Note

esp32

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 :cppadc2_get_raw may get blocked until Wi-Fi stops, and vice versa.

not esp32

Since the ADC2 module is also used by the Wi-Fi, reading operation of :cppadc2_get_raw may fail between :cppesp_wifi_start() and :cppesp_wifi_stop(). Use the return code to see whether the reading is successful.

esp32c3

A specific ADC module can only work under one operating mode at any one time, either Continuous Read Mode or Single Read Mode.
ADC1 and ADC2 can not work under Singel Read Mode simultaneously. One of them will get blocked until another one finishes.
For continuous (DMA) read mode, the ADC sampling frequency (the sample_freq_hz member of :cppadc_digi_config_t) should be within SOC_ADC_SAMPLE_FREQ_THRES_LOW and SOC_ADC_SAMPLE_FREQ_THRES_HIGH.

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.

Note

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

esp32c3

ADC Continuous (DMA) Read mode

Please use the ADC continuous read mode driver as the following steps:

Initialize the ADC driver by calling the function :cppadc_digi_initialize.
Initialize the ADC controller by calling the function :cppadc_digi_controller_config.
Start the ADC continuous reading by calling the function :cppadc_digi_start.
After starting the ADC, you can get the ADC reading result by calling the function :cppadc_digi_read_bytes. Before stopping the ADC (by calling :cppadc_digi_stop), the driver will keep converting the analog data to digital data.
Stop the ADC reading by calling the function :cppadc_digi_stop.
Deinitialize the ADC driver by calling the function :cppadc_digi_deinitialize.

Note

See adc_limitations for the limitation of using ADC continuous (DMA) read mode.

ADC Single Read mode

The ADC should be configured before reading is taken.

For ADC1, configure desired precision and attenuation by calling functions :cppadc1_config_width and :cppadc1_config_channel_atten.

For ADC2, configure the attenuation by :cppadc2_config_channel_atten. The reading width of ADC2 is configured every time you take the reading.

Attenuation configuration is done per channel, see :cppadc1_channel_t and :cppadc2_channel_t, set as a parameter of above functions.

Then it is possible to read ADC conversion result with :cppadc1_get_raw and :cppadc2_get_raw. Reading width of ADC2 should be set as a parameter of :cppadc2_get_raw instead of in the configuration functions.

esp32

It is also possible to read the internal hall effect sensor via ADC1 by calling dedicated function :cpphall_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.

SOC_ULP_SUPPORTED

This API provides convenient way to configure ADC1 for reading from ULP <../../api-guides/ulp>. To do so, call function :cppadc1_ulp_enable and then set precision and attenuation as discussed above.

esp32 or esp32s2

There is another specific function :cppadc_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-api-adc-calibration.

Note

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

Application Example

esp32 or esp32s2

Reading voltage on ADC1 channel 0 ({IDF_TARGET_ADC1_CH0}):

#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 :cppadc_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 ({IDF_TARGET_ADC2_CH7}):

#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

esp32

Reading the internal hall effect sensor:

#include <driver/adc.h>

...

    adc1_config_width(ADC_WIDTH_BIT_12);
    int val = hall_sensor_read();

esp32

The value read in both these examples is 12 bits wide (range 0-4095).

esp32s2

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

Minimizing Noise

The {IDF_TARGET_NAME} 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.

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

ADC Calibration

The :component_file:`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 {IDF_TARGET_NAME}s.

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

{IDF_TARGET_ADC_CALI_SOURCE: default="3", esp32="3", esp32s2="1"}

Calibration values are used to generate characteristic curves that account for the variation of ADC reference voltage of a particular {IDF_TARGET_NAME} chip. There are currently {IDF_TARGET_ADC_CALI_SOURCE} source(s) of calibration values on {IDF_TARGET_NAME}. The availability of these calibration values will depend on the type and production date of the {IDF_TARGET_NAME} chip/module.

esp32

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).
ESP32 Chip Surface Marking
If you would like to purchase chips or modules with calibration, double check with distributor or Espressif (sales@espressif.com) directly.

none

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 {IDF_TARGET_NAME} 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
```

esp32s2

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.

none

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 {IDF_TARGET_NAME} board's port name.

esp32c3

The code example for using ADC single read mode and ADC continuous (DMA) read mode can be found in the peripherals/adc/esp32c3 directory of ESP-IDF examples.

esp32 or esp32s2

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-api-reference-adc-driver
adc-api-reference-adc-calibration
adc-api-reference-gpio-lookup-macros

ADC driver

inc/adc.inc

inc/adc_types.inc

inc/adc_common.inc

ADC Calibration

inc/esp_adc_cal.inc

GPIO Lookup Macros

inc/adc_channel.inc

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adc.rst

adc.rst

Analog to Digital Converter (ADC)

Overview

ADC Limitations

Driver Usage

ADC Continuous (DMA) Read mode

ADC Single Read mode

Application Example

Minimizing Noise

ADC Calibration

Calibration Values

Application Extensions

GPIO Lookup Macros

API Reference

ADC driver

ADC Calibration

GPIO Lookup Macros

Files

adc.rst

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adc.rst

File metadata and controls

Analog to Digital Converter (ADC)

Overview

ADC Limitations

Driver Usage

ADC Continuous (DMA) Read mode

ADC Single Read mode

Application Example

Minimizing Noise

ADC Calibration

Calibration Values

Application Extensions

GPIO Lookup Macros

API Reference

ADC driver

ADC Calibration

GPIO Lookup Macros