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SCD4x — CO2, Temperature & Humidity Sensor

Basics

  • I2C Address: 0x62
  • Library: Sensirion I2C SCD4x
  • Measures: CO2 (ppm), Temperature (°C), Humidity (%RH)

API

#include <SensirionI2cScd4x.h>
#include <Wire.h>
SensirionI2cScd4x scd;

scd.begin(Wire, SCD41_I2C_ADDR_62);
scd.wakeUp();
scd.stopPeriodicMeasurement();
scd.reinit();
scd.startPeriodicMeasurement();  // 5-second interval

// In loop:
bool ready = false;
scd.getDataReadyStatus(ready);
if (ready) {
    uint16_t co2;
    float temp, humidity;
    scd.readMeasurement(co2, temp, humidity);
}

Measurement Modes

Mode Interval Notes
Periodic 5 sec Default, most accurate
Low-power periodic 30 sec Power saving
Single shot 5 sec min SCD41 only

Calibration

  • ASC (Auto Self-Calibration): Enabled by default. Assumes sensor sees 400 ppm (outdoor air) for 4+ hours at least once per week.
  • Forced recalibration: Requires 3+ min operation in known CO2 concentration first.
  • Temperature offset: Compensate for self-heating (0–20°C range). Use setTemperatureOffset().
  • Altitude/Pressure: setSensorAltitude() or setAmbientPressure() for compensation.

Quirks

  • Must call stopPeriodicMeasurement() before changing any config
  • persistSettings() saves to EEPROM — only 2000 write cycles, don't call frequently
  • readMeasurement() returns error if called before data ready
  • All methods return int16_t error code (0 = success)
  • Startup sequence: wakeUp() → stopPeriodicMeasurement() → reinit() → startPeriodicMeasurement()