Adafruit SCD-40 - True CO2, Temperature and Humidity Sensor - STEMMA QT / Qwiic

The SCD-40 is a photoacoustic "true" CO2 sensor that accurately measures the concentration of carbon dioxide (CO2) in ambient air. Unlike sensors like the SGP30, which approximate CO2 levels from VOC gas concentration, the SCD-40 directly measures CO2 in parts per million (PPM), making it a reliable tool for environmental sensing, air quality monitoring, scientific experiments, and ventilation studies. While it is larger and more expensive than some alternatives, it provides precise and authentic CO2 data.

This sensor is a more compact version of the SCD-30, utilizing a different measurement technique that allows it to be smaller while maintaining similar data quality. The SCD-40 uses I2C communication, making it compatible with a wide range of microcontrollers and microcomputers. Both Arduino and Python/CircuitPython libraries are available for quick setup.

There are two variants of this sensor:

• SCD-40: More affordable, ideal for general indoor and outdoor CO2 and air quality measurements. It has a range of 400–2000 PPM with an accuracy of ±(50 PPM + 5% of reading).
• SCD-41: A higher-end model suited for industrial and scientific CO2 measurements, capable of measuring a wider range of 400–5000 PPM with an accuracy of ±(40 PPM + 5% of reading).

The SCD-40 sensor comes mounted on a custom PCB in the STEMMA QT form factor, making it easy to interface with other components. It is compatible with SparkFun Qwiic I2C connectors, allowing for simple, solderless connections between your development board and the sensor, as well as the ability to chain other sensors.

Operating on a voltage range of 3.3V to 5V, the sensor prioritizes a quiet, low-ripple power supply for optimal performance. A 3.3V regulator and level shifters are included to ensure stable voltage, especially when using noisy 5V power sources. For advanced users, the regulator and I2C logic levels can be customized through soldering.