CO2 Monitoring

Monitoring CO2 levels, and temperature with an ESP8266 D1 Mini microcontroller and a Sensirion SCD40 CO2 sensor.

To be connected to a time-series database like InfluxDB...

...or used to manually probe data via the serial monitor...

Sensor used

Environment monitor

The monitor is an SCD40: https://sensirion.com/products/catalog/SCD40

It has an accuracy of:

• CO2 accuracy: ±50.0 ppm
• temperature accuracy: 0.8 °C
• relative humidity accuracy: 6 %RH

Sensirion SCD40 · Sensirion_SCD4x_Datasheet.pdf

Microcontroller used

ESP8266 D1 Mini

How to build

Hardware

Attach the ESP to the SCD40 any which way you desire. Here is one option:

See a pinout reference diagram e.g., this one, and connect:

SDC40	ESP8266
GND (ground)	GND (ground)
VCC (supply voltage)	5V
SCL (SPI clock)	GPIO5 / SCL
SDA (SPI data)	GPIO4 / SDA

Build

First, install https://platformio.org/ as a command line interface (CLI).

To test PlatformIO, upload the "blink" program, which should blink the inbuilt ESP LED once every second.

Test with blink.cpp

# build firmware/software
pio run -e blink
# upload (flash device)
pio run -t upload  -e blink

Test with monitor.cpp

Then, upload the monitor program. This should flash the current CO2 levels on the LED, and output them to serial.

# build firmware/software
pio run -e monitor
# upload (flash device)
pio run -t upload -e monitor
# monitor (serial)
pio device monitor

Once it works, you can run some terminals to view live graphs and a display using the scripts in the monitor-scripts folder. First, log the data to a file env.log using

pio device monitor --quiet | tee -a env.log

Then run each of the scripts like watch ./monitor-scripts/printppm.sh, resulting in something like:

logger.cpp

This is setup to use InfluxDB. First, set up an InfluxDB instance on a server following the guide.

Then, create an API access token, and edit the secrets file:

Project secrets are stored in ./src/secrets.h. There is an example secrets file ./src/secrets.example.h.

This contains:

• InfluxDB secrets (URL, organisationm access token, bucket)
• WiFi secrets (SSID, password)

Install the logger firmware with:

# build firmware/software
pio run -e logger
# upload (flash device)
pio run -t upload -e logger
# monitor (serial)
pio device monitor

You should see any success/error messages in the serial output,