Low-cost headless CO2 sensor, based on ESPHome.
The included config.yaml uses the following components:
- Wemos D1 mini board (or clone). (Cost: ca. 2 EUR)
- Sensirion SCD4x CO2 sensor module. (Cost: ca. 15 EUR)
Connecting the boards will require some soldering, and the type of wire you would like to use.
The case folder contains STL files and their OpenSCAD sources for a simple 3D-printed case.
Connect the D1 Mini board and CO2 sensor module as follows:
| D1 Mini Pin | CO2 Sensor Pin |
|---|---|
| GND | GND |
| 3V3 | VDD |
| SCL | SCL |
| SDA | SDA |
Short M2 screws (~3 mm) should work for the D1 mini board. The sensor module can simply be pushed into its holder.
Connect the D1 Mini board to your computer via USB for the initial firmware installation.
# Create (then customize) secrets.yaml
cp secrets-example.yaml secrets.yaml
# Install firmware with standard configuration
esphome run config.yaml --no-logs
# Install firmware with custom device name
esphome -s name co2sensor42 run config.yaml --no-logsAfter connecting to your Wifi network, the ESPHome web interface should be available at http://co2sensor (or your custom device name).
Prometheus metrics should be available at http://co2sensor/metrics (or your custom device name).
The grafana folder contains example Grafana dashboards.
The hackydash folder contains a simple HTML dashboard.
By default, the SCD4x performs Automatic Self-Calibration (ASC), and does not need to be calibrated manually. However, the data sheet contains this note:
The automatic self-calibration algorithm assumes that the sensor is exposed to the atmospheric CO2 concentration of 400 ppm at least once per week.
If sufficient ventilation cannot be ensured, it might become necessary to perform Forced Recalibration (FRC) using a reference value. The ESPHome web interface contains an FRC button for performing the calibration, and an FRC Reference slider for setting the reference value. Before calibration, the data sheet suggests:
Operate the SCD4x in the operation mode later used in normal sensor operation (periodic measurement, low power periodic measurement or single shot) for > 3 minutes in an environment with homogenous and constant CO2 concentration.
The FRC functionality can be disabled by setting the variable frc to disabled.