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Comment by Havoc | Hacker News Reader

Have experimented with this too - the accuracy is less of a concern to me than the fact that PM sensors require airflow and most achieve that via shitty whiny tiny fans. bzzzzzz

Closest "solution" I've found is the airsensors built into some airfilters. They seem to steal some of the main airflow rather than having a second fan. Obviously not quiet but at least fan size is decent so bit lower pitch

As for other measurements - for temp/humidity/pressure...any sensor will do. CO2 - the SCD41 are best I've found, BME680 and BME688 are hot garbage.

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It really depenends on the PM sensors you use. For the Plantower 5003 we use in our monitors, you only hear a faint noise from the fan when you put it directly at your ear. However some other monitors need an extra fan in the enclosure and some of them can get noisy.

For CO2, the Sensirion SCD41 is a good sensor which uses photo accoustic principle. We found NDIR sensors using light spectometrie to be a bit more accurate like the SenseAir S8. Price wise the two are quite similar.

Can confirm, I have about 8 gradients deployed now, including one in my studio with 31 dBa noise floor, and I can only ever hear the Plantower's fan with my ear nearly touching the device. I've never heard it day to day.

The noisy fan really varies by device. My Air Graident Basic DIY makes very little noise. I have another device I got earlier, a "Lonicera" (some chinese brand) and it looks like it has an extremely similar Plantower PM sensor inside, which is what has the little fan ... but it is often way noiser and rattle-y, the fan is clearly somewhat malfunctioning. I've taken it mostly apart, but it didn't seem worth the effort to go the last mile to fix or replace it.

> BME680 and BME688 are hot garbage.

I agree 100%. What they measure (which is already very non-precise), only vaguely correlates with air quality and there are many factors that would throw off the readings.

Reading from their reference manual, one can already see from all the complicated expressions (regression) and numerical factors that they tried too hard to come up with something that looks like an air quality metric.

> BME680 and BME688 are hot garbage.

I've got a BME680 on a Raspberry Pi reporting the values it senses. I'm confused about how to interpret the air quality readings as far as what is good vs. what should be concerning. Is that what you mean by "hot garbage" or are you not satisfied with the accuracy readings themselves?

They are just not accurate. 25% variability is just not an acceptable level of accuracy. And their results are very dependant on temperature and humidity.

The readings coming out of it are basically meaningless & only vaguely correlate with what's happening it the room

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