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Comment by mypastself | Hacker News Reader

Not to hijack your thread, but I wonder if anyone here’s built their own Raspberry/Arduino CO2 monitor? Which (reliable) sensors did you use? Did you find it more affordable than purchasing a monitor, especially if you already had unused microcontrollers lying around the house?

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I built one based on the AirGradient DIY sensor [1]. It is open source, and you can order PCBs or build them yourself. It is also compatible with ESPHome.

It uses the "Senseair S8" CO2 sensor, which costs a bit (25-30$), but (according to AirGradient) has a very high quality.

[1]: https://www.airgradient.com/open-airgradient/instructions/di...

Seconding this recommendation. I was surprised how easy and cheap it was to order my own tweaked PCBs. Airgradient has also done a lot of testing to determine which components work well and what their different failure modes are.

Depending on how many you build at a time, you can source all the parts for maybe $40-$60. Assembly is straightforward as long as you're comfortable with through-hole soldering (and if not, this is a great chance to learn). The design is also modular enough that it's easy to skip on things like the thermometer or particulate matter sensor if you're so inclined.

I'm currently developing my own monitor based on Sensirion SCD40(CO2/temperature/humidity) and Plantower PMS7003(PM2.5). The SCD40 is lot smaller than any NDIR sensor, but with the same accuracy[1].

My goal is to get a cheap (~$50) sensor in a small package that I can put in every room in my house. It will be modular so I skip the display and the PM2.5 sensor and it can be cheap as ~$25

[1]: https://www.airgradient.com/open-airgradient/blog/co2-sensor...

The microcontroller is the cheapest part! The good sensors that you want to use are in the $45 range. Look for "True" CO2 sensor that use some sort of optical technique to measure CO2. A lot of the really cheap CO2 monitors just measure VOC with some kind of metal element and approximate CO2. I like Sensirion SCD30 or SCD40.

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