Sensirion SCD40 CO2 sensor units for makers: M5Stack UNIT CO2 and TeHyBug ESP8285 device

We just wrote about the Infineon XENSIV PAS CO2 Shield2Go board to measure carbon dioxide (CO2) levels last week, but I’ve just come across two more hardware with a CO2 sensor designed for makers, but based on Sensirion SCD40 sensor instead, and mostly designed to monitor indoor CO2 levels since high concentrations may impact your health negatively.

The first one is the M5Stack UNIT CO2 that’s designed to be connected to one of the company’s Core modules through an I2C interface, and TeHyBug portable mini sensor device equipped with ESP8285 WiFi microcontroller, as well as optional AHT10 temperature & humidity sensor and BMP280 pressure sensor, besides the SCD40 sensor.

M5Stack UNIT CO2

M5Stack UNIT CO2


  • Sensirion SCD40 sensor
    • CO2 Measurement range – 400 ~ 2000 ppm
    • CO2 Sampling accuracy – ±(50 ppm + 5% of reading)
    • Temperature range – -10 – 60°C with 0.8°C   accuracy
    • Humidity range – 0 – 95% RH with 6% RH accuracy
  • Host interface – I2C using 0x62 address
  • Power Supply – 5V via I2C connector, integrated 5V -> 3.3V Buck converter
  • Dimensions – 48 x 24 x 16mm (plastic enclosure)
  • Weight – 7.54 grams

M5Stack provides documentation and Arduino and UIFlow code samples for their ESP32 core boards such as the M5StickC PLUS or M5Stack Atom Lite.

The M5Stack UNIT CO2 can be purchased for $33.90 on the company’s online store.

TeHyBug ESP8285 device

ESP8285 CO2 Sensor board

Contrary to the M5Stack UNIT CO2 sensor, TeHyBug’s device is a standalone board with Sensirion SCD40 CO2 sensor and an Espressif ESP8285 WiFi module, plus optional sensors, OLED display, and 3D printed enclosure

TeHyBug CO2 sensor device specifications:

  • Wireless module – ESP8285 module with 2.4GHz WiFi
  • Sensors
    • Sensirion SCD40 CO2 sensor
    • Optional AHT10 temperature & humidity sensor with respectively ± 0.3°C and ± 2% RH accuracy
    • Optional BMP280 barometric air pressure sensor
    • Support for more via TeHyBug universal sensor connector (4-pin audio jack)
  • Display – Optional 0.66-inch OLED display
  • Debugging/programming – Micro USB port with CH340 chip for flashing and programming
  • Misc
    • 1x mode button (set flashing/programming mode), Reset button, button, 2x user buttons (IO_5 and IO_14)
    • WS2812B RGB LED to report the air quality (green=good, yellow=acceptable, red=bad)
  • Power Supply – 5V via micro USB port or solder pads
  • Dimensions – Tiny
FreshAirMakesSense Board 3.5mm sensor jack OLED display
FreshAirMakesSense board: bottom side with 3.5mm jack for additional sensors (top), the OLED display (bottom)

Since SCD40 can measure temperature and humidity, the AHT10 sensor may seem redundant, but if we look at the details it provides quite better accuracy for both temperature and humidity. The board ships with TechHy CO2 sensor firmware that serves the sensor data directly to HomeAssistant, MQTT, HTTP, etc… You’ll find the firmware, source code (Arduino), and some documentation on Github. But you can really flash any firmware compatible with ESP8266/ESP8285, including ESPHome if you wish.

The video below shows how tiny the device really is, and is connected to an additional temperature/humidity/pressure sensor module through the 3.5mm jack.

YouTube video player

TeHyBug miniature CO2 sensor device is sold on Tindie for $65 to $89 depending on the selected options.

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