RustyMicrobit: Moxi

An air quality sensor based on the excellent video series by The Rust Bits (YouTube, GitHub).

We use the micro:bit's LED display to encode the current temperature, humidity, and CO2 levels. The exact reading for each is shown on-demand via the microbit's buttons (A, B, and capacitive logo).

The CO2 sensor provides temperature and relative humidity readings while compensating for atmospheric pressure.

Display

Read column-by-column from left to right:

• Temperature
  • Starting from the bottom, each LED represents 10 degrees F,
  • {50, 60, 70, 80, 90}
• Temperature
  • Starting from the top, each LED represents 2 degrees F
  • {1, 3, 4, 5, 7, 9}
• CO2
  • Starting from the bottom, each LED represents 200 ppm CO2
  • {400, 600, 800, 1000, 1200}
• CO2
  • Starting from the top, each LED represents 40 ppm CO2 but starting at 0
  • {0, 40, 80, 120, 160}
    • Interpreted as {20, 60, 100, 140, 180} +/- 20
• Humidity
  • Starting from the bottom, each LED represents 20% relative humidity except for the final LED indicating a relative humidity above 90%
    • A prospective particulate sensor cautions against use when the relative humidity is above 90%
  • {20, 40, 60, 80, 90}
    • Interpreted as {30, 50, 70} +/- 10, over 80, over 90

Therefore, the display reads 73F, 940 +/- 20 ppm CO2, 70% +/- 10% relative humidity

Hardware

Components

• Main board: micro:bit v2
• CO2 Sensor: SCD40 or SCD41
• Pressure Sensor: BMP581

Connectors

• micro:bit Breakout
• Qwiic MultiPort
• Qwiic Cables

Layout

graph TD;
    A["micro:bit"]-->B(["micro:bit Breakout"]);
    B(["micro:bit Breakout"])-->C(["Qwiic MultiPort"]);
    C(["Qwiic MultiPort"])-->D["CO2 Sensor"];
    C(["Qwiic MultiPort"])-->E["Pressure Sensor"];

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