co2-sensor

This repository contains the code for a simple CO2 sensor that exports metrics using the prometheus monitoring format, and potentially others in the future.

Assembly

Parts

The hardware is relatively simple, only using 3 parts:

• A Telaire T6615. This may be overkill. A T6613 may also work. I think all Telaire CO2 sensors use the same protocol, so any other Telaire sensore should work as well.
• A Raspberry Pi Zero W Any other device capable of UART and 5 volt supply would work as well. All Pi variants should work.
• A logic-level converter between 3.3v and 5v. The RPi's UART is 3.3v and the Telaire sensor's logic operates at 5v so a converter is needed. I'm using an Adafruit 4-Channel Converter, but other cheaper converters should work as well.

Wiring Schematic

TODO: Write something nicer.

Configuring the Raspberry Pi Zero

• Use the RPI OS Imager to install the image onto an SD Card. Install Raspberry Pi OS Lite.
• On the boot partition, add an empty file named ssh.
• On the booth partition, add a wpa_supplicant.conf file as instructed here.
• Boot the device, and connect via SSH.
• Run sudo raspi-config
• In raspi-config: 1 System Options > S1 Wireless Lan, then setup WiFi.
• In raspi-config: 3 Interface Options > P2 SSH, then enable SSH.
• In raspi-config: 3 Interface Options > P6 Serial Port, then disable login over serial, and enable the serial port. Do not enable login over the serial port, it will make serial communication unreliable.
• Quit and re-boot.

Building + Loading the Program

• Install Rust's cross and start the Docker daemon as mentioned in the instructions.

• In backend/ run:

  cross build --target=arm-unknown-linux-gnueabihf --release
  

  This builds a release binary of the backend that can run on a Raspberry Pi Zero W.

• Copy the binary over to the Raspberry Pi. Still in backend/ run:

  RASPBERRY_PI_IP=10.0...  # Replace with actual IP
  scp target/arm-unknown-linux-gnueabihf/release/co2 pi@$RASPBERRY_PI_IP:~
  

  To copy the server binary to the Raspberry Pi.

• In frontend/, run:

  rm -r dist/  # to clean up any previous builds.
  yarn run parcel build src/index.html
  

  To build the frontend.

• Still in frontend/ copy the frontend onto the Pi using a command like:

  RASPBERRY_PI_IP=10.0....  # Replace with actual IP
  rsync -hurt dist/ pi@$RASPBERRY_PI_IP:~/frontend
  

• Finally, ssh onto the Pi, and run the server:

  RASPBERRY_PI_IP=10.0...  # Replace with actual IP
  ssh pi@$RASPBERRY_PI_IP
  # Now on the PI
  sudo ./co2 ./frontend /dev/serial0
  # Note, you may need to use /dev/serial1 if not using a Raspberry Pi Zero W
  

Configuring the Sensor

Configuration of the sensor is done through the sensor's web interface. Browse to the web interface by going to http://<your raspberry pi IP> in your web browser of choice, or http://raspberrypi.local (potentially substituting for a different hostname if you've changed it). On that page is a "Calibrate" button, when pressed it will walk through the calibration process.

NOTE: Calibration currently doesn't signal very will if calibration fails, but info will be printed in the server's log if the device fails to calibrate correctly, so check there after calibration.

Reading Measurements

The current CO2 reading is displayed on the web-interface at http://<your raspberry pi IP>. The web interface also provides a /metrics endpoint (http://<your raspberry pi IP>/metrics) that can be scraped by the open source Prometheus monitoring software.