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Comment by Havoc | Hacker News Reader

I managed to find some cheap <20 SDC41 sensors on aliexpress (they’re normally closer to 50).

True co2, not equivalent like say the bme680. Previously used equivalent ones and the data is tangibly better. Highly recommend.

Can’t figure out a good way to do pm2.5 without a whiny fan though. The unit I’ve got has a barely audible high pitched whine

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My home brew weather/air quality station is seemingly totally silent, though the PM sensor does have a fan. I've never heard it.

https://partofthething.com/thoughts/weather-and-air-quality-...

off topic - did you get your geiger counter wired in?

Not really. I did do enough work to be able to read count rate from a ESP8266 [1] but never actually installed it in the weather station. Since then, I got a scintillator detector [2] with a USB soundcard interface which would be way better for a weather station since it could actually identify isotopes in addition to count rate. So you could get alerts like "oh dang, I-131 detected in the air, take shelter."

[1] https://partofthething.com/thoughts/making-true-random-numbe...

[2] https://www.youtube.com/watch?v=AxXnUXrditI

I have built CO2 monitors using MH-Z19B, Senseair S8 (same detector used in the AirGradient kits), and the SDC41 modules and my favorite is the S8. It seems equally accurate to the SDC41 and is easier to keep calibrated.

It also has a pin that is enabled when the CO2 level exceeds 1000 ppm so you can build a useful monitor using nothing more than an LED and an old USB power adapter.

Yes I agree. The SenseAir S8 is probably the best of the three. The SCD41 gives similar values indoors but at lower concentrations outdoors it seems to become less accurate. The MH-Z-19 is also pretty good but I think the S8 has a better built quality and less noise in the measurements.

Can you post links here. I bought one in AliExpress and the readings were highly variable when there was no change in quality (as far as I can tell. Outdoor weather hasn't changed. I didn't cook, etc..)

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