OpenCO2 Mini is an Arduino IDE compatible repository for an ultra-compact indoor air quality monitor using the ESP32-S3, STCC4, SHT40, and a RGB led. Designed for portability and seamless smartphone connection via USB-C, this mini version prioritizes a smaller footprint while delivering precise CO2, temperature, and humidity readings. Ideal for on-the-go monitoring, it helps maintain health and productivity by alerting to poor air quality—perfect for offices, classrooms, or travel. With low power consumption and open-source design, it's easy to customize and integrate into smart home setups.
Buy it here on Tindie
The OpenCO2 Mini features the Sensirion STCC4, CO2 Sensor and a SHT40 Sensor for temperature and humidity measurement. Utilizing the latest technological advancements in thermal conductivity sensing, the fully factory calibrated STCC4 provides the accuracy needed for indoor air quality applications at a low current consumption. This compact Gadget ensures reliable long-term performance with automatic baseline correction.
- CO2 output range: 400 ppm – 5'000 ppm
- Accuracy:
- CO2 ±(100 ppm + 10% m.v.)
- Temperature ±0.8°C
- Humidity ±2%
The color LED provides real-time readings of CO2 levels in a convenient traffic‑light pattern. Updates occur every few seconds for instant feedback, with low power draw enabling portable use.
Built-in 2.4GHz ESP32-S3 Wi-Fi allows for remote data access and integration. Connect to your home network for web-based monitoring or smart home compatibility.
Add this configuration to your configuration.yaml file in Home Assistant. Replace OpenCO2Mini with the device's IP if needed.
rest:
scan_interval: 60
resource: http://openco2mini:9925/
method: GET
sensor:
- name: "CO2"
device_class: carbon_dioxide
unique_id: "d611314f-9010-4d0d-aa3b-37c7f350c82f"
value_template: >
{{ value | regex_findall_index("(?:rco2.*})(\d+)") }}
unit_of_measurement: "ppm"
- name: "Temperature"
unique_id: "d611314f-9010-4d0d-aa3b-37c7f350c821"
device_class: temperature
value_template: >
{{ value | regex_findall_index("(?:atmp.*})((?:\d|\.)+)") }}
unit_of_measurement: "°C"
- name: "Humidity"
unique_id: "d611314f-9010-4d0d-aa3b-37c7f350c822"
device_class: humidity
value_template: >
{{ value | regex_findall_index("(?:rhum.*})((?:\d|\.)+)") }}
unit_of_measurement: "%"
Transparent with ultra-compact size: ~1.5cm x 2.0cm for easy connection to every USB-C outlet.
The Sensirion MyAmbience app (available for iOS and Android) brings your OpenCO2 Mini to life via Bluetooth Low Energy (BLE), offering a user-friendly interface to view live CO2, temperature, and humidity data, plot historical trends, and export measurements. Download the app from the App Store or Google Play, enable Bluetooth on your phone, and scan for the OpenCO2 Mini inside the app. It connects seamlessly for real-time monitoring on the go. To add WiFi connection credentials, open the app after pairing, navigate to the device settings menu, under "Gadget's WiFi Connection" add your WiFi network Network Name (SSID) and Password, and "Set Wifi Credentials". The OpenCO2 Mini will then join your home network for enhanced integrations like Home Assistant or remote access while maintaining Bluetooth functionality for mobile viewing.
Once connected, query metrics via curl: curl [IP]:9925/metrics or http://openco2mini:9925/ Example output:
# HELP rco2 CO2 value, in ppm
# TYPE rco2 gauge
rco2{id="Open CO2 Mini",mac="B4:3A:45:AD:DA:28"}1797
# HELP atmp Temperature, in degrees Celsius
# TYPE atmp gauge
atmp{id="Open CO2 Mini",mac="B4:3A:45:AD:DA:28"}18.92
# HELP rhum Relative humidity, in percent
# TYPE rhum gauge
rhum{id="Open CO2 Mini",mac="B4:3A:45:AD:DA:28"}72.76
Use internet-pi to store the CO2 / Temperature / Humidity data on your Pi. First connect the OpenCO2 Sensor to your Wi-Fi network and follow the instructions https://www.youtube.com/watch?v=Cmr5VNALRAg Then download the https://raw.githubusercontent.com/davidkreidler/OpenCO2_Sensor/main/grafana_OpenCO2_Sensor.json and import it into Grafana.
Download FIRMWARE.BIN from the latest release
Connect the OpenCO2 Mini via USB-C.
Press the button for a few seconds until the LED shines in rainbow colors.
Copy the file to the USB mass storage device.
Install the ESP32-S3 support for Arduino IDE
Choose ESP32S3 Dev Module under Tools -> Board -> esp32
Connect the Sensor via USB-C while pressing the button and choose the new Port under Tools -> Port
