Adafruit SGP40 Air Quality Sensor Breakout - VOC Index - STEMMA QT/Qwiic

The VOC Index is a processed, unitless value from 0 to 500 calculated by the sensor's internal algorithm from the raw MOX signal. It provides a relative measure of overall air quality, where lower values indicate better air. It is designed for trend analysis and comparison rather than reporting absolute concentrations of specific gases.

The board uses a standard I2C interface at address 0x59. You can connect it directly to microcontrollers like Arduino or Raspberry Pi using the 4-pin STEMMA QT / Qwiic JST connector for solderless wiring, or by soldering to the broken-out 0.1" pitch pads for VCC, GND, SDA, and SCL.

The sensor is factory calibrated, but like all MOX sensors, its response can vary and drift over time. For precise measurements, calibration against a known reference is recommended. For general monitoring of trends and relative changes, the factory calibration is sufficient. Utilizing the built-in humidity compensation feature with an external humidity sensor will also improve accuracy.

Humidity compensation allows the SGP40 to adjust its VOC reading based on ambient relative humidity, reducing cross-sensitivity. To use it, you must have a separate humidity sensor (e.g., SHT31). You then read the RH% value from that sensor and write it to a specific register on the SGP40 via I2C, after which subsequent VOC readings will be compensated.