[HN Gopher] Infineon's CO2 Sensor Monitors Indoor Air Quality
___________________________________________________________________
Infineon's CO2 Sensor Monitors Indoor Air Quality
Author : WaitWaitWha
Score : 187 points
Date : 2024-09-21 19:08 UTC (1 days ago)
(HTM) web link (www.allaboutcircuits.com)
(TXT) w3m dump (www.allaboutcircuits.com)
| vardump wrote:
| Finally an actually working (cheap?) CO2 sensor?
|
| So many of those actually measure humidity, temp and VOCs and try
| to derive some sort of CO2 reading out of those.
| IgorPartola wrote:
| This was my thought exactly. I used sensors that were about
| $25/each in the past and those worked well but this would be
| seemingly way easier to integrate and get ahold of.
| vardump wrote:
| $25 for a CO2 sensor component that actually works is not bad
| at all.
| tobi1449 wrote:
| Sensirion SCD41 should be pretty good, right? You can get
| them for ~25 USD on aliexpress ...
| ale42 wrote:
| I'm not sure I would source non-Chinese electronic
| components from Aliexpress... (unless it's just to play
| with them, definitely not for a product): you might need
| to check their reliability and quality. Pretty sure that
| Sensirion themselves are not selling there, so they are
| probably either clones, fakes, recycled ones, or if you
| are lucky authentic ones that for some reason ended up
| there (but I can't imagine a way).
| throwup238 wrote:
| _> or if you are lucky authentic ones that for some
| reason ended up there (but I can 't imagine a way)._
|
| Chinese fabs are notorious for running secret shifts that
| make their customers' chips to sell themselves. They're
| the exact same chip but made without authorization, using
| the customer's exact design.
|
| That said, Sensirion has their own CMOS fabs in
| Switzerland so that's very unlikely to be the case here.
| If they work at all, the counterfeit chips are probably
| some Chinese CO2 sensor IC that's small enough to fit
| into the same package, lightly customized to fit the
| pinout of the original. Or it's just a microcontroller
| inside faking it a la FTDI.
| radicality wrote:
| I got mine from M5Stack and works quite well, I'm
| submitting data every 5 seconds using
| EspHome/HomeAssistant
| fuzzy2 wrote:
| Sensirion has the SCD40, which appears to be based on the same
| principle. It's much cheaper than the SCD30.
| _blk wrote:
| Yes, SCD30 series are optical while SCD40 series are
| photoacoustic. STC series are thermal conductivity based. STC
| and SCD40 are smaller than SCD30 but less accurate if memory
| serves (check datasheet).
| rainburg wrote:
| The Senseair S88, which was released earlier this year, costs
| ~$22/piece, or ~$13/piece if you order more than 100.
| tzs wrote:
| It's not really "finally". They introduced a similar sensor,
| the PASCO2V01, a couple years ago. That one has been available
| on a breakout board with the necessary support hardware from
| SparkFun for over a year [1].
|
| Comparing the datasheets for the PASCO2V01 and the new
| PASCO2V15 the old one actually seems a little better as far as
| CO2 measuring performance goes. They are the same on most
| things, but the old one has slightly better accuracy.
|
| The new one is +-(50 ppm + 5%) between 400 ppm and 3000 ppm.
|
| The old one is +-(30 ppm + 3%) between 400 ppm and 5000 ppm.
|
| The big difference is this:
|
| > Infineon has recently introduced the PASCO2V15, a new 5 V
| sensor to improve air quality monitoring in building
| environments.
|
| Both of them require a dual voltage power supply. They both
| want 3.3 V for their digital components and a higher voltage
| for their IR emitter.
|
| For the older one that higher voltage is 12 V. For the newer it
| is 5 V.
|
| [1] https://www.sparkfun.com/products/22956
| fnordpiglet wrote:
| Iirc they were merged into esphome last year too.
| Animats wrote:
| True. The cheap ones are trying to guess CO2. Those are called
| "indoor air quality sensors".
|
| Small CO2 sensors have been available for years, for about $50.
| Compare [1].
|
| Life of this new device is only 10 years, which is short for
| HVAC systems. A hotel might have a thousand of these. Older
| devices say "15+" years.
|
| All these devices have a calibration problem. They drift. They
| try to correct by treating the lowest value they ever see as
| "normal" (that's about 400 ppm CO2 today, vs 300 PPM in 1950)
| and recalibrating. So they're not useful for observing a
| general increase in CO2. They're also not useful for
| greenhouses, where CO2 levels may drop below ambient CO2 due to
| photosynthesis. Manual recalibration is possible but requires
| feeding in pure nitrogen and a known nitrogen/CO2 mixture.[2]
|
| Devices which don't need that re-calibration exist.[3] They're
| more complicated. Also don't seem to be stocked by the usual
| distributors.
|
| [1]
| https://rmtplusstoragesenseair.blob.core.windows.net/docs/pu...
|
| [2] https://www.co2meter.com/blogs/news/7512282-co2-sensor-
| calib...
|
| [3] https://www.murata.com/en-
| us/products/sensor/co2/overview/te...
| brianglick wrote:
| Do you know of anywhere at all to get one of the devices that
| don't require re-calibration?
| Animats wrote:
| That is a really good question.
|
| Murata announced this in 2019, and there's a part number
| (IMG-CA0011-00/ IMG-CA0012-00/IMG-CA0023-00) and a full
| data sheet.[1] But no distributor has it. Not DigiKey,
| Mouser, Arrow, or Newark. Even Octopart doesn't list it.
| It's on Murata's list of recommended products, not the
| discontinued list. Try contacting Murata.
|
| [1] https://go.murata.com/rs/382-MEZ-125/images/HC%20CO2-se
| nsor%...
| nimish wrote:
| 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.
|
| Neither are cheap, around $25-40 each in small quantities. The
| infineon one has a full blown microcontroller handling the
| operation of the sensors.
|
| 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.
| shadowpho wrote:
| 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)
| clumsysmurf wrote:
| I worked in a building 500 ft from a busy highway and when I
| cleaned my desk it always had black dust on it.
|
| Along these lines of air quality, can anyone recommend a
| similarly advanced PM2.5 / PM10 sensor under $100 / ea?
| trog wrote:
| I haven't gotten their PM sensor unit but have a CO2 sensor
| from CO2.click. About to pull the trigger on a PM sensor but
| just deciding which one. The founder there is active on a few
| places including Mastodon and I really like my CO2 sensor from
| them.
|
| Edit: sorry missed your price guidance. They are quite a bit
| more so probably not what you're after!
| christina97 wrote:
| Have been using a Plantower PMS5003 for a while with ESPhome
| and it's pretty good.
| seper8 wrote:
| Please get an air purifier with a HEPA filter...
|
| Ikea sells a reasonable air purifier AND seperate sensors
| nowadays!
| e44858 wrote:
| Sensirion SEN54.
|
| It also measures temp/humidity/voc, and has a built-in fan to
| speed up the response time.
| dzhiurgis wrote:
| Would be nice if they packaged these up in laptops - fan is
| already there and always running.
| Genbox wrote:
| Datasheet can be found here:
| https://www.infineon.com/dgdl/Infineon-PASCO2V15-DataSheet-v...
| FL33TW00D wrote:
| 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.
| crazygringo wrote:
| I'm not sure how accurate that would be on your wrist, because
| the proportion of recently exhaled air would be so much higher,
| since it's only a foot or two from your mouth.
|
| CO2 monitors often have little silent fans to draw in fresh air
| as well, for accuracy.
| christina97 wrote:
| I don't think it'd make a difference. I've got one on my desk
| in front of me and can't detect a difference with me at the
| desk vs not.
| stevenhuang wrote:
| Unless your room has really good airflow you should be able
| to tell quite clearly.
|
| I have an SCD41 and I see a large spike in readings less
| than a minute after sitting down at my desk.
| triwats wrote:
| This is super interesting for me - but I'd love to put it on a
| bicycle (they are often locked up and stationary - for example)
| but move at faster speeds. Maybe this means they are only
| useful at tracking information when locked/stationary?
|
| I really like the idea of using cheap (?) devices in a sort of
| mesh to feed back telemetry data on pollution. Pollution is
| everyone's concern, so visualising that would be cool.
|
| Interested to hear if you had any more thoughts on this!
| carstenhag wrote:
| Related: cheap device to track pollution + mesh +
| visualization: https://luftdaten.info/
|
| Once had this thing on a balcony of a shared flat in
| Heilbronn, Germany. Wondered what that was, previous tenant
| told me about it and it was never removed from there.
| rapjr9 wrote:
| The Bikenet project mapped CO2 in a small town:
|
| https://www.cs.dartmouth.edu/~sensorlab/pubs/BikeNet-
| SenSys0...
| sbierwagen wrote:
| Note that NDIR sensors use a surprising amount of power, since
| they're based around an incandescent bulb shining light through
| the sample volume. A CO2 wearable will need to be recharged
| once a day, like a smart watch.
| seper8 wrote:
| I'd wear this! This would also be very cool to share with
| others, form like a network to get a clearer picture of air
| quality
| FL33TW00D wrote:
| It only became possible to do it in a wearable form factor
| very recently using a combination of the following 2 sensors:
| https://sensirion.com/products/catalog/STCC4
| https://www.bosch-
| sensortec.com/media/boschsensortec/downloa...
|
| Not sure the market is big enough to invest my time.
| akira2501 wrote:
| > to get a clearer picture of air quality
|
| A wearable CO2 monitor would do the opposite of this.
|
| If you want to measure quality you need fixed location
| devices.
| OldGuyInTheClub wrote:
| 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.
| babl-yc wrote:
| Seems similar to the SCD40 photoacoustic approach.
|
| I used that for an open-source CO2 monitor I designed:
|
| https://bitclock.io/
|
| https://github.com/goat-hill/bitclock
| ahaucnx wrote:
| Great project, lovely design and super cool that it's also open
| source hardware.
|
| We at AirGradient open sourced our monitors around 2 years ago
| and this has been the best decision for our company.
| JSDevOps wrote:
| https://aranet.com/en/home/products/aranet4-home?srsltid=Afm...
| elliottkember wrote:
| Like that, but cheaper and more accurate.
| thadk wrote:
| I believe Aranet4 contains this NDIR optical sensor
| https://www.co2meter.com/collections/sensors/products/006-0-...
| ahaucnx wrote:
| 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.
|
| 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.
|
| 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.
|
| However, outdoors they significantly underperform optical NDIR
| sensors to the extent that they are barely usable. See for
| example this chart [2].
|
| 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.
|
| 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.
|
| 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.
|
| [1] https://www.airgradient.com/blog/co2-sensors-photo-
| acoustic-...
|
| [2] https://www.airgradient.com/blog/co2-sensors-photo-
| acoustic-...
| wkat4242 wrote:
| Interesting. But why would you monitor CO2 outdoors? Even the
| NDIR ones just return "400" when they detect outdoor air and
| use it as calibration.
|
| Though i believe you can turn off the auto calibration which is
| probably a good idea in busy city areas where I imagine outdoor
| CO2 is slightly higher than 400. And manually calibrate them
| with an actual known source.
| ahaucnx wrote:
| Outdoor CO2 levels can go up to 700-800ppm in rural areas due
| to plants creating CO2 [1]. I was initially surprised it's
| that high but it was verified with reference instruments.
|
| Why measure CO2 outdoors?
|
| We are able to detect emission sources pretty well now with
| our outdoor monitors [2] that have the SenseAir S8 NDIR
| sensor built in. You can see some real data in the blog post
| I wrote about launching our global CO2 map [3].
|
| So setting up a dense network of these sensors in a city
| would allow to measure if for example the introduction of
| low-emission zones or switching to electric buses etc. would
| work.
|
| Another use case is to check for leakage in underground CO2
| storage facilities.
|
| All-in-all it's still experimental (to some extent) but we
| know the accuracy is there and we can see more and more use
| cases as outlined in my blog post. So we now work hard to get
| more and more of these sensors out there to get more data to
| identify additional use cases.
|
| [1] https://www.airgradient.com/blog/performance-of-low-cost-
| co2...
|
| [2] https://www.airgradient.com/outdoor/
|
| [3] https://www.airgradient.com/blog/airgradient-global-
| co2-map/
| Rebelgecko wrote:
| Who do you calibrate these CO2 sensors in areas where the
| background level is so high?
| ahaucnx wrote:
| Not sure what you mean with calibration here. Above is
| not so much about calibration but correlation. Basically
| comparing the monitors to the reference data.
| hyperknot wrote:
| I think he meant How?, meaning normally a calibration is
| placing indoor monitors outdoors for 20 mins.
| avianlyric wrote:
| If you're using reference grade instruments, I would
| assume they're calibrated in labs using well controlled
| environments.
|
| I.e. put sensor in vacuum chamber, remove all gases, then
| introduce know amount of gases to produce a known target
| environment.
|
| Given their reference instruments, I assume they're also
| capable of maintaining their calibration for a long
| period of known time, before they need to be re-
| calibrated. They would never rely on something as
| inaccurate as "20 mins outdoors" to calibrate themselves.
| darby_nine wrote:
| Surely this refers to decomposition and not living plants.
| Your link doesn't appear to finger plants as the culprit at
| all.
| avianlyric wrote:
| Plants produce CO2 as well, photosynthesis is only used
| to produce sugars, normal respiration (I.e. sugars + O2 =
| energy + CO2), is used by plants to consume those sugars.
|
| Only a plant cells containing chlorophyll and exposed to
| sunlight will photosynthesise. Notably at night there
| isn't much sunlight, so normal respiration dominates a
| plants gas conversion processes, and results in them
| producing net CO2.
|
| Based on the graphs in the blog post, I assume GP is
| placing the CO2 production on plants because it the CO2
| levels peak at night, then return to normal every
| morning.
| mschuster91 wrote:
| Yep, I've noticed this as well with my cannabis grow
| tent. At an 18/6 lighting schedule, it's noticeable that
| CO2 grows up to 800ppm in the tent at the end of the
| fake-night cycle.
| neilv wrote:
| > _Outdoor CO2 levels can go up to 700-800ppm in rural
| areas due to plants creating CO2 [1]._
|
| We need to get those rural voters more oxygen, STAT!
| nroets wrote:
| Em, do you know that plants are actually a net source of
| oxygen ? And a sink of CO2 ?
| tedivm wrote:
| Net, sure, but it's actually really really complex when
| you look at point in time numbers.
|
| > Carbon dioxide is not released during photosynthesis,
| but small amounts of that gas are emitted both day and
| night as a by-product of cellular respiration. It is
| worth noting that the majority of plants absorb carbon
| dioxide during the day for photosynthesis and do so in
| greater amounts than they release for cellular
| respiration.
|
| So depending on the time plants could easily be pushing
| out more CO2 than they are pulling it _at that time_ ,
| which could result in CO2 concentrations increasing
| during that time.
| Projectiboga wrote:
| Time dependent, plants give off O2 in the evening. The
| co2 is released by the micro organisms which are
| bacterial and fungal and breathe O2 just like us.
| stavros wrote:
| Plants are overall a sink of CO2, as it goes into
| building their mass.
| specto wrote:
| It seems like ozone is the missing piece. The only ones
| that measure outdoor ozone are governments, and the numbers
| keep increasing.
| TeMPOraL wrote:
| Isn't the increasing numbers good here at this point? Or
| not at this altitude?
| RF_Savage wrote:
| No it is not. Ozone is not good for breathing.
| cyberax wrote:
| > Interesting. But why would you monitor CO2 outdoors?
|
| For example, to know that it's futile to try to turn on
| ventilation to lower the indoor CO2 concentration.
| crazygringo wrote:
| Yup. In my city, on windy winter days the CO2 is as low as
| it gets, in the low 400's.
|
| But on a hot windless summer day in a temperature
| inversion, my meter will read 700 or even 800 outdoors, as
| the CO2 from vehicles and maybe even power plants just sits
| around without going anywhere.
|
| In the winter, if my indoor reading is 800 I open the
| window a crack to improve my concentration. On certain days
| in the summer, I just accept it's going to be 1,000 indoors
| and there's nothing I can do about it.
| iforgotpassword wrote:
| Interesting. I never gave this whole thing much of a
| thought, but always assumed co2 levels would be higher
| during winter as there's no green outside to absorb it,
| plus everyone turning on the central heating systems.
| moogly wrote:
| The Infineon press release talks about indoor monitoring only,
| and it is even present in the title, but I have noticed that
| you guys consider HN to be a very important marketing channel,
| so I get it.
| ahaucnx wrote:
| If you take the time and actually read the blog post I linked
| to, you will see that mostly it is about indoor CO2.
|
| However, to understand the performance of these different
| sensor technologies it is important to point out that they
| fail under certain environmental conditions, e.g. outdoors.
| dr_kiszonka wrote:
| If you have time, could you write a bit more about the humming
| phenomenon?
| OldGuyInTheClub wrote:
| Photoacoustic is usually done with a chopped or pulsed light
| source at a few hundred Hz (ie. audio frequencies). If the
| molecules don't absorb at that wavelength or if the molecules
| are not present, the light just goes through. If light is
| absorbed, there will be slight heating when the beam is on
| resulting in a sound wave at the chopping/pulsing frequency.
| This is detected by the microphone. For weak absorptions, the
| intensity of the sound wave will be linear in the
| concentration.
|
| I think this is what is meant by "humming": There is a sound
| that is generated when the target molecule is present.
| OldGuyInTheClub wrote:
| Optical linewidths are influenced by temperature and pressure.
| Outdoors, humidity can be a factor as well. When I did
| photoacoustic spectroscopy, we used two or more wavelengths in
| the measurement; one on resonance, one off resonance to help
| with background discrimination. I am not sure whether these
| ultracompact instruments have that capability.
|
| Additionally, contaminants on any surface the light strikes
| will generate spurious signals. Lock-in (synchronous) detection
| at the optical source modulation frequency can help get rid of
| a lot of noise but if the noise appears at that frequency, it
| will corrupt the measurement.
|
| This classic paper from 1986 covers a lot of what can be done
| with the technique and how to do it correctly. Reviews of
| Modern Physics is behind a paywall but there's a copy on the
| web at the URL below. Applications of
| photoacoustic sensing techniques Andrew C. Tam Rev.
| Mod. Phys. 58, 381 - Published 1 April 1986
|
| http://users.df.uba.ar/dkunik/photothermal/review/tam86.pdf
| ckocagil wrote:
| 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.
|
| Hopefully this method doesn't have the same restriction.
| koolba wrote:
| > 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.
|
| 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?
| zootboy wrote:
| It's saying that it could be either +/-50 ppm from the actual
| reading, or +/-5% from the actual reading, whichever is worse.
| metaphor wrote:
| > _It 's saying that it could be either +/-50 ppm from the
| actual reading, or +/-5% from the actual reading, whichever
| is worse._
|
| No, it's stacked, and strictly applicable between 400-3000
| ppm as characterized (despite 0-32000 ppm operating range by
| design).
|
| At the lower 400 ppm end, accuracy is +/- 50 ppm +/- 20 ppm =
| +/- 70 ppm.
|
| At the upper 3000 ppm end, accuracy is +/- 50 ppm +/- 150 ppm
| = +/- 170 ppm.
|
| Also worth noting that the calibrated reference used to
| determine this published accuracy has an uncertainty of +/-
| 2%; ref datahseet[1] Table 7.
|
| Caveat emptor: this published accuracy can't be trusted at
| face value when sampling more than 1 meas/min; ref ibid.[1]
| Table 4.
|
| [1] https://www.infineon.com/dgdl/Infineon-
| PASCO2V15-DataSheet-v...
| skykooler wrote:
| It's $26 on Mouser, which seems like a reasonable price.
| sbierwagen wrote:
| I built a CO2 meter around a SCD30 five years ago:
| https://bbot.org/blog/archives/2024/05/19/pocket_co2_meter_b...
|
| 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.
| londons_explore wrote:
| 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.
|
| 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.
|
| [1]: https://www.aliexpress.com/w/wholesale-z19-co2.html?
| IgorPartola wrote:
| There is a way to program these?
| londons_explore wrote:
| they're just ST microcontrollers. you can put your own
| firmware on and do what you like with the hardware.
|
| The hardware consists of an incandescent bulb and photodiode
| with amplifier and high res ADC.
|
| The bulb and photodiode sit in a box with a silvered
| interior, which allows light from the bulb to reflect around
| inside the box a lot (and having some light absorbed by CO2)
| before hitting the photodiode.
___________________________________________________________________
(page generated 2024-09-22 23:01 UTC)