Analog To Digital Sensor

The Analog To Digital (adc) Sensor allows you to use the built-in ADC in your device to measure a voltage on certain pins.

  • ESP8266: Only pin A0 (GPIO17) can be used.

  • ESP32: GPIO32 through GPIO39 can be used.

  • RP2040: GPIO26 through GPIO29 can be used.

../../_images/adc-ui.png 
# Example configuration entry
sensor:
  - platform: adc
    pin: GPIOXX
    name: "Living Room Brightness"
    update_interval: 60s

Configuration variables:

  • pin (Required, Pin): The pin to measure the voltage on. Or on the ESP8266 or Raspberry Pi Pico it could alternatively be set to VCC, see Measuring VCC.

  • attenuation (Optional): Only on ESP32. Specify the ADC attenuation to use. See ESP32 Attenuation. Defaults to 0db.

  • raw (Optional): Allows to read the raw ADC output without any conversion or calibration. See Different ESP32-ADC behavior since 2021.11. Defaults to false.

  • samples (Optional): The amount of ADC readings to take per sensor update. On the ESP32 this value is ignored if attenuation is set to auto. Defaults to 1.

  • update_interval (Optional, Time): The interval to check the sensor. Defaults to 60s.

  • All other options from Sensor.

Note

This component prints the voltage as seen by the chip pin. On the ESP8266, this is always 0.0V to 1.0V Some development boards like the Wemos D1 mini include external voltage divider circuitry to scale down a 3.3V input signal to the chip-internal 1.0V. If your board has this circuitry, add a multiply filter to get correct values:

sensor:
  - platform: adc
    # ...
    filters:
      - multiply: 3.3

ESP32 Attenuation

On the ESP32 the voltage measured with the ADC caps out at ~1.1V by default as the sensing range (attenuation of the ADC) is set to 0db by default. Measuring higher voltages requires setting attenuation to one of the following values: 0db, 2.5db, 6db, 12db. There’s more information at the manufacturer’s website.

To simplify this, we provide the setting attenuation: auto for an automatic/seamless transition among scales. Our implementation combines all available ranges to allow the best resolution without having to compromise on a specific attenuation.

Note

In our tests, the usable ADC range was from ~0.075V to ~3.12V (with the attenuation: auto setting), and anything outside that range capped out at either end. Even though the measurements are calibrated, the range limits are variable among chips due to differences in the internal voltage reference.

ESP32 pins

ADC2 pins are only usable when Wi-Fi is not configured on the device.

Variant

ADC1

ADC2

ESP32

GPIO32 - GPIO39

GPIO0, GPIO2, GPIO4, GPIO12 - GPIO15, GPIO25 - GPIO27

ESP32-C3

GPIO0 - GPIO4

GPIO5

ESP32-S2

GPIO1 - GPIO10

GPIO11 - GPIO20

ESP32-S3

GPIO1 - GPIO10

GPIO11 - GPIO20

Different ESP32-ADC behavior since 2021.11

The ADC output reads voltage very accurately since 2021.11 where manufacturer calibration was incorporated. Before this every ESP32 would read different voltages and be largely inaccurate/nonlinear. Users with a manually calibrated setup are encouraged to check their installations to ensure proper output. For users that don’t need a precise voltage reading, the “raw” output option allows to have the raw ADC values (0-4095 for ESP32) prior to manufacturer calibration. It is possible to get the old uncalibrated measurements with a filter multiplier:

# To replicate old uncalibrated output, set raw:true and keep only one of the multiplier lines.
raw: true
filters:
  - multiply: 0.00026862 # 1.1/4095, for attenuation 0db
  - multiply: 0.00036630 # 1.5/4095, for attenuation 2.5db
  - multiply: 0.00053724 # 2.2/4095, for attenuation 6db
  - multiply: 0.00095238 # 3.9/4095, for attenuation 12db
  # your existing filters would go here

Note we don’t recommend this method as it will change between chips, and newer ESP32 modules have different ranges (i.e. 0-8191); it is better to use the new calibrated voltages and update any existing filters accordingly.

Measuring VCC

The following configuration block adds the sensor reflecting VCC on a supported hardware platform. Please see specific sections below of what voltage is actually measured.

sensor:
  - platform: adc
    pin: VCC
    name: "VCC Voltage"

On ESP8266

On the ESP8266 you can even measure the voltage the chip is getting. This can be useful in situations where you want to shut down the chip if the voltage is low when using a battery.

To measure the VCC voltage, set pin: to VCC and make sure nothing is connected to the A0 pin.

Note

To avoid confusion: It measures the voltage at the chip, and not at the VCC pin of the board. It should usually be around 3.3V.

On Raspberry Pi Pico

On the Raspberry Pi Pico and Pico W the ADC can measure VSYS voltage.

Depending on how VSYS is powered the readings will have different meanings - either power supply voltage when it is connected to VSYS pin directly, or USB voltage (VBUS) minus some drop on the Schottky diode the Raspberry Pi Pico has between those pins. Our experiments indicate the drop being ~0.1V for Pico and ~0.25V for Pico W; you can use sensor filters to adjust the final value.

Note

On Raspberry Pi Pico W the ADC GPIO29 pin for VSYS is shared with WiFi chip, so attempting to use it explicitly will likely hang the WiFi connection. It is recommended to use VCC as ADC pin in that case.

RP2040 Internal Core Temperature

The RP2040 has an internal temperature sensor that can be used to measure the core temperature. This sensor is not available on the GPIO pins, but is available on the internal ADC. The below code is how you can access the temperature and expose as a sensor. The filter values are taken from the RP2040 datasheet to calculate Voltage to Celcius.

sensor:
  - platform: adc
    pin: TEMPERATURE
    name: "Core Temperature"
    unit_of_measurement: "°C"
    filters:
      - lambda: return 27 - (x - 0.706f) / 0.001721f;

Multiple ADC Sensors

You can only use as many ADC sensors as your device can support. The ESP8266 only has one ADC and can only handle one sensor at a time. For example, on the ESP8266, you can measure the value of an analog pin (A0 on ESP8266) or VCC (see above) but NOT both simultaneously. Using both at the same time will result in incorrect sensor values.

Measuring battery voltage on the Firebeetle ESP32-E

This board has a internal voltage divider and the battery voltage can easily be measured like this using 12dB attenuation on GPIO34.

- platform: adc
  name: "Battery voltage"
  pin: GPIO34
  accuracy_decimals: 2
  update_interval: 60s
  attenuation: 12dB
  samples: 10
  filters:
    - multiply: 2.0  # The voltage divider requires us to multiply by 2

This works on SKU:DFR0654. For more information see: manufacturer’s website.

See Also