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ADC

About

ADC (analog to digital converter) is a very common peripheral used to convert an analog signal such as voltage to a digital form so that it can be read and processed by a microcontroller.

ADCs are very useful in control and monitoring applications since most sensors (e.g., temperature, pressure, force) produce analogue output voltages.

Note

Each SoC or module has a different number of ADC's with a different number of channels and pins availible. Refer to datasheet of each board for more info.

Arduino-ESP32 ADC API

ADC common API

analogRead

This function is used to get the ADC raw value for a given pin/ADC channel.

uint16_t analogRead(uint8_t pin);
  • pin GPIO pin to read analog value

This function will return analog raw value (non-calibrated).

analogReadMillivolts

This function is used to get ADC raw value for a given pin/ADC channel and convert it to calibrated result in millivolts.

uint32_t analogReadMilliVolts(uint8_t pin);
  • pin GPIO pin to read analog value

This function will return analog value in millivolts (calibrated).

analogReadResolution

This function is used to set the resolution of analogRead return value. Default is 12 bits (range from 0 to 4096) for all chips except ESP32S3 where default is 13 bits (range from 0 to 8192). When different resolution is set, the values read will be shifted to match the given resolution.

Range is 1 - 16 .The default value will be used, if this function is not used.

Note

For the ESP32, the resolution is between 9 to12 and it will change the ADC hardware resolution. Else value will be shifted.

void analogReadResolution(uint8_t bits);
  • bits sets analog read resolution

analogSetAttenuation

This function is used to set the attenuation for all channels.

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.

The measurable input voltage differs for each chip, see table below for detailed information.

.. tabs::

   .. tab:: ESP32

      =====================  ===========================================
      Attenuation            Measurable input voltage range
      =====================  ===========================================
      ``ADC_ATTEN_DB_0``     100 mV ~ 950 mV
      ``ADC_ATTEN_DB_2_5``   100 mV ~ 1250 mV
      ``ADC_ATTEN_DB_6``     150 mV ~ 1750 mV
      ``ADC_ATTEN_DB_11``    150 mV ~ 2450 mV
      =====================  ===========================================

   .. tab:: ESP32-S2

      =====================  ===========================================
      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
      =====================  ===========================================

   .. tab:: ESP32-C3

      =====================  ===========================================
      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
      =====================  ===========================================

   .. tab:: ESP32-S3

      =====================  ===========================================
      Attenuation            Measurable input voltage range
      =====================  ===========================================
      ``ADC_ATTEN_DB_0``     0 mV ~ 950 mV
      ``ADC_ATTEN_DB_2_5``   0 mV ~ 1250 mV
      ``ADC_ATTEN_DB_6``     0 mV ~ 1750 mV
      ``ADC_ATTEN_DB_11``    0 mV ~ 3100 mV
      =====================  ===========================================


void analogSetAttenuation(adc_attenuation_t attenuation);
  • attenuation sets the attenuation.

analogSetPinAttenuation

This function is used to set the attenuation for a specific pin/ADC channel. For more information refer to analogSetAttenuation.

void analogSetPinAttenuation(uint8_t pin, adc_attenuation_t attenuation);
  • pin selects specific pin for attenuation settings.
  • attenuation sets the attenuation.

ADC API specific for ESP32 chip

analogSetWidth

This function is used to set the hardware sample bits and read resolution. Default is 12bit (0 - 4095). Range is 9 - 12.

void analogSetWidth(uint8_t bits);

Example Applications

Here is an example of how to use the ADC.

.. literalinclude:: ../../../libraries/ESP32/examples/AnalogRead/AnalogRead.ino
    :language: arduino

Or you can run Arduino example 01.Basics -> AnalogReadSerial.