In the cold season we tend to keep the windows closed. The air gets "stale": humidity often rises above 60 %, which can harm our wellbeing and promote mould. At the same time the CO₂ level in the air increases, which impacts our ability to concentrate.

So I built a room air monitor that stays unobtrusive as long as everything is in the green zone, but becomes deliberately noticeable once thresholds are exceeded. For my personal love of statistics I also visualise the measurements in a clear dashboard.

There are lots of commercial gadgets like that.

Most of the affordable CO2 meters are relative, not absolute. They set their 400 PPM level based on the lowest value they ever see. That's usually OK, but it's not good enough for places with permanent people occupancy, such as nursing homes. Absolute detectors with NIST calibration are available but around US$500.[1]

[1] https://www.forensicsdetectors.com/products/carbon-dioxide-d...

Cool project. I've done something similar using defunct crypto Awair AQI sensors tied into Home Assistant. They have an LED panel in the front that can show overall AQI or any of the pollutants they track: https://www.getawair.com/products/element

The sky is the limit as to what you can do with Home Assistant automations.

It's surprising how quickly a room with a closed door and one person can go from ~ambient CO2 levels to 1000ppm+.

> The air gets "stale": humidity often rises above 60 %,

Fun - I have the opposite problem, humidity goes down to almost nothing and we have to use humidifiers to keep it around 40% to avoid horrible nose/throat/skin dryness.

Forced air hvac is probably why.

You should find a friend's garage, shop or hackerspace with a brake, and metal cutting tools.

I have a similar monitor for equipment metrics, and the cardboard design is similar to the stand I made out of metal. I powder coated the metal light beige and it looks professional.

I was looking for cheap co2 sensors that can be deployed on RPi but I guess they all feel expensive.

Germans sure love their Lüften

This is cool! How does it compare to e.g. an Aranet4? I got one to detect when there is a high risk of COVID-19 aerosols lingering and generally carry it in my bag. That way I can check the reading using my phone.