We did some extensive testing of photo-acoustic and optical NDIR CO2 sensors indoors as well as outdoors and also in comparison to scientific reference instruments.<p>I just updated the blog post that I wrote last year [1] with the specs of this new Infineon sensor and also our experiences with doing CO2 measurement outdoors.<p>In summary we can say that under normal indoor conditions (e.g. small range of temperature, relative high range of CO2 etc.), the photo-acoustic NDIR sensors perform well.<p>However, outdoors they significantly underperform optical NDIR sensors to the extent that they are barely usable. See for example this chart [2].<p>It's hard to say why exactly they perform so poorly outdoors but I believe that they rely on quite complex internal algorithms that probably have been only developed with typical indoor conditions in mind and as soon as some parameters like temperature are out of the typical range, they significantly drop in their performance.<p>Furthermore, we also detected that they are sensitive to interference from low frequency noise which could for example come from ventilation systems, refrigerators etc. This is not surprising as they rely on their internal microphone to do the photo-acoustic measurements.<p>All of this and the rock-solid performance we see with optical NDIR sensors made us quite wary about the photo-acoustic sensors and not use them in our open-source hardware monitors. As I said, I believe they work quite well in general but because we saw also some really strange and unexpected behavior of these photo-acoustic sensors, I'd now always prefer optical NDIR sensors if possible.<p>[1] <a href="https://www.airgradient.com/blog/co2-sensors-photo-acoustic-vs-ndir-updated/" rel="nofollow">https://www.airgradient.com/blog/co2-sensors-photo-acoustic-...</a><p>[2] <a href="https://www.airgradient.com/blog/co2-sensors-photo-acoustic-vs-ndir-updated/#outdoors" rel="nofollow">https://www.airgradient.com/blog/co2-sensors-photo-acoustic-...</a>
Nice to see this miniaturization of photoacoustic spectroscopy - something I've done a bit of in the past. It is an underappreciated technique. Ordinarily one measures the difference in optical throughput with and without a sample. If it is a weak absorber, it is a difference between two large numbers. PAS is zero background. No absorption, no pressure wave, no signal. Any absorption stands out clearly against that zero background.
Seems similar to the SCD40 photoacoustic approach.<p>I used that for an open-source CO2 monitor I designed:<p><a href="https://bitclock.io/" rel="nofollow">https://bitclock.io/</a><p><a href="https://github.com/goat-hill/bitclock">https://github.com/goat-hill/bitclock</a>
I have used the MH-Z19 [1] $10 real CO2 sensors for a bunch of things. They appear to work well, although I have no ability to measure the accuracy of the results.<p>I do have a 'one day when I get free time' plan to make new firmware for them to also measure moisture and a bunch of other VOC's which have unique absorption spectra in the 800-2000nm range, since the hardware itself can be abused as a poor-man's spectrometer.<p>[1]: <a href="https://www.aliexpress.com/w/wholesale-z19-co2.html" rel="nofollow">https://www.aliexpress.com/w/wholesale-z19-co2.html</a>?
Finally an actually working (cheap?) CO2 sensor?<p>So many of those actually measure humidity, temp and VOCs and try to derive some sort of CO2 reading out of those.
I worked in a building 500 ft from a busy highway and when I cleaned my desk it always had black dust on it.<p>Along these lines of air quality, can anyone recommend a similarly advanced PM2.5 / PM10 sensor under $100 / ea?
They've had a 12v version for a while, and it's quite nice despite the high voltage requirement. I made a little breakout with a boost converter. Sensirion has a slightly smaller sensor as well, SCD41 that I think works on similar principles.<p>Neither are cheap, around $25-40 each in small quantities. The infineon one has a full blown microcontroller handling the operation of the sensors.<p>To keep accuracy you would need to have a CO2 gas setup which isn't cheap either, but for indoor use I don't think it matters.
I’ve been considering designing a wearable that monitors CO2 and PM2.5 continuously, but I’m unsure if people would wear it in conjunction with an Apple Watch or similar.
The problem with the common CO2 sensor modules is they don't have DC accuracy. Meaning they rely on the device being present in place where it regularly (e.g at least once a week) gets exposed to fresh air, which the module sets as its baseline. This works because fresh air has roughly the same CO2 concentration everywhere.<p>Hopefully this method doesn't have the same restriction.
> With this architecture, the sensor achieves a high level of precision, offering an accuracy of ±50 ppm ±5% between 400 ppm and 3,000 ppm. The overall range of the sensor is from 0 to 32,000 ppm.<p>What does the back to back ± mean? Is that the variance of accuracy from device to device? Or does the 5% reference the specific range of 400-3000?
I built a CO2 meter around a SCD30 five years ago: <a href="https://bbot.org/blog/archives/2024/05/19/pocket_co2_meter_before_it_was_cool/" rel="nofollow">https://bbot.org/blog/archives/2024/05/19/pocket_co2_meter_b...</a><p>My takeaway is that it draws a lot more power than you'd expect, thanks to the incandescent light source, and unless there's quite a lot of airflow over the sensor, it'll exhibit self-heating at any poll rate under every ten minutes.
Have been using scd30/31/40. Great sensors. This one requires a bit more power but would be interesting to see price as it seems it actually measured CO2. (A lot of other sensors simulate it with measuring alcohols and assume people breathing which gives poor results)
Datasheet can be found here: <a href="https://www.infineon.com/dgdl/Infineon-PASCO2V15-DataSheet-v01_30-EN.pdf?fileId=8ac78c8c914a3ac8019179fecd0c351d" rel="nofollow">https://www.infineon.com/dgdl/Infineon-PASCO2V15-DataSheet-v...</a>