Resources:

Schematic
KiCad Files
Hookup Guide
Datasheets:

STC31
SHTC3

STC Field Calibration Guide
STC Design-In Guide

SparkFun CO2 Sensor STC31 Qwiic Board for Accurate Gas Concentration Measurement
The SparkFun CO2 Sensor STC31 (Qwiic) is a compact, high-accuracy gas sensing module designed for precise carbon dioxide measurement in embedded and environmental monitoring applications. Built around the Sensirion STC31 thermal conductivity CO2 sensor, the board delivers calibrated gas concentration and temperature outputs, supporting both CO2 in nitrogen and CO2 in air. Its wide measurement range and fast start-up time make it suitable for laboratory equipment, HVAC systems, industrial safety, indoor air quality monitoring, and research projects where reliable CO2 data is essential.
To improve accuracy across changing environmental conditions, the board integrates a Sensirion SHTC3 humidity and temperature sensor, allowing real-time compensation for humidity and ambient temperature variations. With Qwiic I2C connectivity, configurable I2C addresses, and onboard jumpers for power LED and pull-up control, the STC31 Qwiic board is optimised for easy integration into Arduino, Raspberry Pi, and other 3.3 V I2C-based systems.
Key Features:

CO2 Sensor IC: Sensirion STC31 thermal conductivity CO2 sensor
Measurement Capability: Calibrated CO2 concentration and temperature output
Calibration Media: Calibrated for CO2 in nitrogen and CO2 in air
Wide Measurement Range: Supports 025 vol% and 0100 vol% CO2 concentration
High Accuracy: Accurate and repeatable CO2 measurements for critical applications
Environmental Compensation: Integrated Sensirion SHTC3 sensor for humidity and temperature correction
Qwiic Interface: Dual Qwiic connectors for solder-free I2C connectivity
Configurable Hardware: Adjustable I2C addresses, power LED, and I2C pull-ups