[paulgerhardt]

For this task I absolutely love my Xiaomi Mijia indoor air quality sensor[1].

Under $50, nice touch screen, WiFi, TVOC, PM2.5, CO2, temp, humidity. Have one by a laser cutter (particulate), one in a paint booth(TVOC), and one in the office conference room (when the CO2 is higher than 1200 its time for a fresh air). A+ product and so much better than what I could build myself at that price point. If you find yourself in mainland China do yourself a favor and drop into a Xiaomi store.

[1]https://m.mi.com/commodity/detail/1184500007

[throwaway9d0291]

I'm not sure about this particular sensor but Xiaomi doesn't have a good track record when it comes to accuracy when it comes to air particulates [0]. Also they claim to use a combined Sensirion TVOC + CO2 sensor, however the only TVOC + CO2 sensors Sensirion offers (SVM30, SGP30) [1] merely estimate CO2 concentration based on H2 levels, they don't actually measure it directly. These sensors tend to be wildly inaccurate. The spec sheet even says typical accuracy is 15%, which is pretty bad.

0: https://smartairfilters.com/en/blog/xiaomi-particle-counter-...

1: https://www.sensirion.com/en/environmental-sensors/gas-senso...

[close04]

I plan on building something with the CCS811 and SGP30 just for comparison sake. This article was interesting [0].

[0] https://www.jaredwolff.com/finding-the-best-tvoc-sensor-ccs8...

[magicalhippo]

I found this[1] article rather interesting, comparing the tVOC and CO2 measured by a consumer device with professional grade equipment. It seems the MOX sensor used in the consumer device (AMS iAQ-CORE-C) did rather well on tVOC, but poorly on CO2 as you mentioned.

[1]: https://www.j-sens-sens-syst.net/7/373/2018/ (pdf on the right)

[throwaway9d0291]

The study is interesting but I wouldn't say it "did rather well", as they applied a calibration to it first:

"A regression analysis was performed to improve the accuracy of the Foobot FBT0002100 data relative to the GrayWolf data. Field calibration equations were then produced from the calibration dataset using the results from the GrayWolf instruments as dependent variables and the Foobot FBT0002100 as independent variables and tested on the validation dataset. An analysis in SPSS of the linear, quadratic, and cubic models was performed individually for each parameter to find the most accurate equation."

You can't do that unless you happen to have access to a different research quality sensor. If the Foobot had that out of the factory it'd be nice though.

[magicalhippo]

That's not how I read it.

"Field calibration equations were then produced from the calibration dataset [...]" (emphasis mine).

Table 3 shows the calibration dataset for tVOC, which at least to me looks rather ok except for the outlier E.

[swebs]

>Xiaomi

Hmmm, does this by chance require an internet connection to operate?

[dotancohen]

I think that I could get by even with the Chinese menus, but the real problem for me is the mobile app. Is the mobile app strictly _required_ or is it an optional feature? I won't use a device that requires an app on my phone to function.

[r3bl]

I have never touched their air purifier, but I did three other gadgets (TV box, some indoor camera, some light bulbs).

If privacy is your concern, I wouldn't recommend them. If stability is your concern, I wouldn't recommend them.

The light bulb works with an app only (probably to remove the need for a separate hub), the camera could be rooted to work offline-only (which is why I bought it, but I gave up after a couple of shots and it's currently sitting in my drawer), and the TV box is by far the noisiest device in my local network. It's like 60% of all DNS requests blocked by my Pi-hole.

Their devices are also the most unstable devices I own, to the point where I'm considering just throwing them in the trash and re-investing in another camera and a TV box. I've already replaced the bulb I've purchased with a Philips Hue system. Quite more expensive, but truly works locally.

[joshefin]

I have the same experience - Xiaomi makes good and cheap hardware, but the software and reliability are bad. And if you want to keep your data private, skip them.

[dotancohen]

Is it linux or freebsd based? Can the firmware be reflashed?

[gwilkes]

Couldn't tell from the link, is there an English language option on the device?

[paulgerhardt]

Yes as well as Fahrenheit temperature if you prefer. Importing outside of China is a fairly highly mark up - $80 on BangGood: https://www.banggood.com/Xiaomi-Mijia-Air-Quality-Tester-Hig...

[tobtoh]

Although on the link you supplied, it does state "Note: Currently only supports Chinese interface display"

[throwaway9d0291]

You can skip Banggood and save a bit. It's $52 from Xiaomi's official store [0] and $8 shipping from a forwarder [1], so $60 total.

[0]: https://detail.tmall.com/item.htm?id=582112668204

[1]: https://www.superbuy.com/en/page/query/freight/#areaId%3D3%2...

[bentpins]

$64 on AliExpress. Pandacheck is a good tool for price comparison although it doesn't help deal with listings with multiple prices https://www.aliexpress.com/item/32970668564.html https://en.pandacheck.com

[throwaway8941]

>when the CO2 is higher than 1200 its time for a fresh air

That's hilarious. Where I am from, in winter it's always at least 1500 ppm outside, and more than 2000 ppm after ~19:00.