CO2 Ampel for ESPHome – Multi-Sensor Board

A simple yet powerful CO2 monitor for ESPHome: ready to use out of the box with Home Assistant!

We aimed to create something easy to use—no more dealing with finicky displays showing tiny, hard-to-read numbers. Our CO2 monitor is different. At its core is a large LED ring that provides a clear visual cue when air quality is poor and it’s time to open a window. Even children can easily understand it! On the technical side, you still get full access to all data in Home Assistant, enabling automations. Additionally, you can control the LED ring and buzzer directly to play notification sounds or display status updates from other systems.

The Vision: The best sensor hardware, professionally built and owned by you! Take back control—no proprietary protocols or locked-down firmware. The CO2 Ampel is built around the ESPHome ecosystem: the firmware is fully open source, and the configuration is readily available, allowing you to (re)flash the device yourself at any time. Misconfigured something? No problem—just visit flash.linkgear.net to reflash the stock firmware.

But what does “best sensor hardware” mean?

• CO2 (Carbon Dioxide) Sensor: Sensirion SCD41
  Photoacoustic NDIR sensor technology “PASens®”, measuring real CO2, with a measurement range of 0 – 40,000 ppm and a sensor lifetime of over 10 years.
• Temperature, Humidity, Pressure Sensor: Bosch BME280
  This sensor does not only directly provide the atmospheric pressure compensation for the CO2 sensor, it also offers a measuring range from -40 to 65° C and a humdity range from 0 – 100 %RH with high resolution.
• Illuminance Sensor: ROHM Semi BH1750FVI-TR
  Allows you to see illuminance with a range of 1 – 65535 lx directly in Home Assistant. Perfect to check if a room is illuminated.

Cool, what else?

• LED ring: 8 individually addressable LEDs SK6812. Setting just one pixel for notifications? No problem!
• Buzzer: The onboard buzzer allows you to play notification tones!
• Microcontroller: featuring a ESP32-WROOM-32E with 8MB flash, enough for even the biggest mods and ideas.
• USB-C Port: Power your CO2 Ampel using USB-C. The USB-C port is also attached to a Skyworks/Silicon Labs CP2102N, allowing you to access the serial port easily.
• Extensibility: A QWIC port allows you to add additional i2c accessories easily.

Looking for an enclosure? We got you covered. A 3d printable enclosure is available on printables.

📗 Documentation