SGP41 VOC and NOx Sensor

• Overview
• ESPHome config
  • Calibration config
• References

Overview

This sensor does not output aboslute values of $VOC$ or $N{O}_x$, but instead it reports an index value for $VOC$² and $NOX$³.

• Typical $VOC$ index: $100$¹
• Typical $N{O}_x$ index: $1$¹

For more details, see the datasheet.

ESPHome config

Set up an an I²C bus first.

i2c:
  - id: i2c_sgp4x
    sda: ${gpio_sda}
    scl: ${gpio_scl}

And use the sgp4x component⁴ to configure sensors for voc and nox:

sensor:
  - platform: sgp4x
    i2c_id: i2c_sgp4x
    address: 0x59
    store_baseline: "${sgp4x_store_baseline}"
    voc:
      id: voc
      name: "VOC"
      icon: "mdi:air-filter"
      device_class: aqi
      state_class: measurement
      unit_of_measurement: "index points"
    nox:
      name: "NOx"
      id: nox
      device_class: aqi
      state_class: measurement
      unit_of_measurement: "index points"
    update_interval: 60s

This sensor operates on $1Hz$ cycles and will be read out on device once per second. However the update_interval config for the sgp4x component will only affect how often the state is reported (defaults to 60s).

Calibration config

• store_baseline: The baseline values are persistently stored on the sensor and applied when the sensor boots. Cleared after OTA.
• voc
  • index_offset: $VOC$ index representing typical conditons, used as an offset.
• nox
  • index_offset: $N{O}_x$ index representing typical conditons, used as an offset.
• compensation: Used to calculate absolute humidity for the sensor to imrove the internal operations of the sensor.
  • temperature_source: ESPHome id for a temperature sensor (reporting in Celsius).
  • humidity_source: ESPhome id for a (relative) humidity sensor.

There are some calibration settings for this sensor:

sensor:
  - platform: sgp4x
    # ...
    store_baseline: true
    voc:
      index_offset: 100
    nox:
      index_offset: 100
    compensation:
      temperature_source: esphome_temperature_sensor
      humidity_source: esphome_humidity_sensor

If store_baseline is set to true the calibration settings are saved on the sensor and loaded on boot.

References