CO2 monitoring with Prometheus

This reads from the CO2 Meter and makes it available as a Prometheus service. The core logic comes from this hackaday article.

Setup

Note this assumes you are running on a Raspberry Pi running Raspberry Pi OS (Bullseye)

1. Install Python 3
2. Install the monitor with python3 -m pip install co2mini[homekit] (remove [homekit] if you don't use HomeKit)
3. Set up CO2 udev rules by copying 90-co2mini.rules to /etc/udev/rules.d/90-co2mini.rules
4. Set up the service by copying co2mini.service to /etc/systemd/system/co2mini.service
5. (Optional) Put a configuration file (see Configuration section below) in /etc/co2mini.env
6. Run systemctl enable co2mini.service

Configuration

The /etc/co2mini.env file contains the environment variables used to configure co2mini beyond the defaults. This is mostly necessary when enabling MQTT.

Example:

MQTT_ENABLED=true
MQTT_BROKER=localhost

MQTT/Home Assistant

The MQTT feature is meant to work with Home Assistant, although nothing bad will happen if you just want to use the MQTT messages directly.

When co2mini starts up, it will send out the discovery message that Home Assistant expects, as well as responding to homeassistant's status when coming online. Be sure those are enabled in the Home Assistant MQTT integration (usually is enabled by default) if you have any issues.

To configure co2mini, the following environment variables are available:

Variable	Default	Description
NAME	co2mini	This is used for the default display name of the device in Home Assistant
MQTT_ENABLED	False	Used to enable/disable sending information over MQTT
MQTT_BROKER	localhost	MQTT Broker hostname
MQTT_PORT	1883	MQTT broker port number (1883 is the standard MQTT broker port)
MQTT_USERNAME		Username for authenticating to MQTT broker (leave blank if no authentication is needed)
MQTT_PASSWORD		Password for authenticating to MQTT broker (leave blank if no authentication is needed)
MQTT_DISCOVERY_PREFIX	homeassistant	Prefix for sending MQTT discovery and state messages.
MQTT_RETAIN_DISCOVERY	False	Flag to enable setting retain=True on the discovery messages. You probably don't need this.
MQTT_OBJECT_ID	co2mini_{HOSTNAME}	Override for setting the object_id in Home Assistant. Default builds using the hostname of the device.

Homekit

If you have the homekit dependencies installed, on the first startup you will need to check the logs to get the setup code to integrate with Homekit. You can find the code using journalctl -u co2mini.service or possibly by checking the status with systemctl status co2mini.service.

Note also that it's sometimes possible that co2mini will have some errors logged and won't be reporting in Homekit anymore. If this happens, it seems like the easiest thing to do is to remove the device from your homekit, remove the accessory.state file in your home (rm accessory.state) and restart co2mini (sudo systemctl restart co2mini.service) to get a new code to pair.

Special notes for Dietpi users

• Be sure to install Python3 pip as well (ID 130)
• Make sure the dietpi user is in plugdev group (sudo usermod -aG plugdev dietpi)