When HN users recommended it
2 HN users recommended this between 2018 and 2024, in 2 comments.
20072026
Each tall tick is one HN user's first recommendation. A short tick is the same user again. Click a tick to jump to the comment.
2 HN users recommended this between 2018 and 2024, in 2 comments.
Each tall tick is one HN user's first recommendation. A short tick is the same user again. Click a tick to jump to the comment.
Slight tangent: Can anyone recommend a decent air quality sensor in the sub-$100 range? I've been curious lately about measuring PM2.5, VOCs, etc. but haven't found a good option.
The sensor in the article looks really nice (Twitter thread mentions https://www.amazon.com/Digital-Quality-Detector-Tester-Monit... as something similar. Twitter thread also links the exact product on Aliexpress, but I refuse to link Aliexpress here since that site is nearly malware).
But the problem with that sensor and all the other sensors I've found thus far (HPMA115S0, SDS011) is I can't be sure how accurate at all they are. I'm not looking for scientific grade stuff here, but if the sensor is off by a factor of two, for example, it's a bit useless isn't it? Especially if I have no idea how far off it is.
For example, I found this research paper: https://www.researchgate.net/publication/322628807_Developme...
If I'm reading it correctly they show that the SDS011 sensor is completely useless for PM10 measurements. For PM2.5 it can be off by a factor of 2 under certain conditions. They were able to come up with a calibration formula that makes it much more accurate (on PM2.5), but I have no way of knowing if their calibration formula is "universal" for the SDS011 or if the constants would vary from unit to unit.
And all of those problems on a device that is marketed as being +-15% accurate. Being off by a factor of two is well beyond 15%...
I haven't dug too deeply yet. Are there better sensors? The HPMA115S0 is brand name at least, but again I have no way of knowing for sure what its real error bounds are. Is there some way to calibrate these things at home without buying an expensive, more accurate sensor (thus defeating the purpose of the cheap sensor)?
It seems a lot of hobby projects end up using these cheap sensor anyway, even if they could be completely wrong? Maybe I'm being too picky and an error of 100% isn't a huge deal?
DIY medical testing is only a part of the DIY testing boom.
Just one small example is the amazing array of test strips we have for liquids: Pool test strips, drinking water test strips, urine test strips, blood test strips, drug (urine) test strips, pregnancy (urine) test strips, and much more.
Back during the COVID-19 pandemic, I set up 2 air particle checkers that returned the number of particles they found in each of (maybe 8) sizes. I put them in 2 clear tubes, and duct taped a COVID-19 mask between the tubes. A pair of fans moved air over the first checker, then through the mask, then through the second checker. I proved that below 2.5 microns, none of the COVID-19 masks people were wearing at work did anything. That was when I started laughing at the whole thing. This is the kind of tester I used: https://www.amazon.com/Digital-Quality-Detector-Tester-Monit... Checking if the testers read the same without a mask was a simple as taping the tubes together without a mask between them.
The electronic meters we have today is astounding. Digital meters that do not use test strips can measure dozens of gasses, from any explosive gas to O2, CO2, CO, LP (I know it's not a liquid when it's a gas, but they call it LP) and dozens more such gasses. The MQ series is really cool: https://robocraze.com/blogs/post/mq-series-gas-sensor
Note: The web links are not things I put up, and I do not make money off them. I only found them through web searches while knowing what subject matter I wanted to find.