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SGP40 — MOX VOC Gas Sensor

Basics

  • I2C Address: 0x59 (fixed)
  • Library: Adafruit SGP40 Sensor
  • Measures: Raw gas signal + computed VOC Index (0–500)

API

#include "Adafruit_SGP40.h"
Adafruit_SGP40 sgp;

sgp.begin();                                    // init + self-test (500ms)
uint16_t raw = sgp.measureRaw(tempC, humidity); // raw signal
int32_t voc = sgp.measureVocIndex(tempC, humidity); // VOC Index 0-500

Temperature/Humidity Compensation

SGP40 requires ambient temp and humidity for accurate VOC calculation. Defaults to 25°C / 50% RH if not provided. We use SCD4x readings for this.

VOC Index Algorithm (Sensirion)

  • Proprietary algorithm with internal state tracking
  • 45-second blackout — returns 0 until algorithm has enough data
  • Continuous learning: adapts baseline over ~12 hours
  • Index 100 = average conditions; >100 = worsening; <100 = improving
  • Gating: freezes estimator during high VOC events (up to 180 min)
  • State can be saved/restored with VocAlgorithm_get_states() / set_states()

Tunable Parameters

Parameter Default Range Description
voc_index_offset 100 1–250 Baseline offset
learning_time_hours 12 1–72 Time to adapt
gating_max_duration_min 180 0–720 Max freeze during high VOC
std_initial 50 10–500 Initial standard deviation

Quirks

  • 250ms delay built into each measurement command
  • Self-test runs during begin() — takes 500ms
  • CRC8 (poly 0x31) on all I2C responses
  • softReset() affects ALL I2C devices on the bus
  • Read interval: 1 second recommended