I would recommend checking out the AQ-SPEC program [1]. They do quite comprehensive tests on low-cost air quality sensors. My side project with a few friends [2] chose to use the Sensirion SPS30 [3] for our portable PM2.5 monitor. As mentioned by others, it's a bit more expensive than the PMS5003 used by AirGradient, but we preferred its documentation, company reputation, and form factor at the time of choosing (2019). The PMS5003 is perfectly capable, and has demonstrated good success with many projects/companies using the sensor (e.g. PurpleAir). However, a quick search suggests there are some issues with a recent batch of these sensors [4].
Open source diy is wonderful. But is there a reliable trustworthy monitor that can just... Be bought? A box that will reliably tell me what's the carbon dioxide carbon monoxide dust allergens volatile compounds? Am I possibly being greedy and I need several konitors (I wouldn't have an issue with that)?
Every review I check for any consumer accessible device seems to indicate they're inaccurate, miscalibrated, or downright deceptive :-(
I got the uHoo Air Quality Monitor[1] and I love it. One of the few nice smart-home/app ones to monitor carbon monoxide too. But it's pricey. I can probably get some discount codes from them if the HN community is interested (I've spoken with their team once before in Singapore and they were very nice and accommodating!)
The Aranet has worked well for me, and I think is calibrated well and works smoothly. It’s not the cheapest though, but I haven’t recharged it in over a year… almost two years now!
The Airthings View Plus is a good one. It has high quality (for consumer) particulate, CO2, VOC and Radon sensors and a good interface. Also tracks temperature, pressure, and humidity for completeness.
For PM2.5, the Qingping Air Monitor (or the Lite version if you prefer that) is good. The review I've read found it has decent accuracy, and, though I haven't tested it rigorously myself, the readings seem reasonable in my experience. The main reason I recommend it, though, is that the UI is great: it keeps graphs of past values that are easy to access, both on the screen and in the app.
On the topic of allergens, I wasn't able to find any device that can measure that.
$15 from AliExpress including shipping. If you are concerned about accuracy, could you not take it outdoors to see how it measures the unaffected atmosphere, then bring it back indoors to see how it compares? For instance, if you are concerned that the 900 PPM reading in your bedroom is inaccurate, you could take it outside and see how it reads compared to the expected ~420 PPM. You might be off by a few PPM, but would it not be accurate enough to see if you are approaching dangerous levels?
It does use auto calibration, which means you need to bring it outside for a few minutes every once in a while (7 days IIRC). Not doing it will not break it, but the readings will drift downward (sensor assumes that the lowest reading it gets in a period of time must be 400 ppm) - and will be fixed in a few minutes outside (few minutes of <400 ppm sets lowest reading to 400).
For folks who want to do something similar (no CO2 measure, and possibly less accurate) for far less per sensor, you can easily connect an ESP8266 ($5) to an IKEA VINDRIKTNING ($16) air quality sensor[1]. Stick a AM2302 ($7) on the outside and you get PM2.5, temperature and humidity for about $30.
I will note though, CO2 measure indoors can be very valuable. Higher levels of CO2 result in less brain function, as shown by this Tom Scott video: https://youtu.be/1Nh_vxpycEA
I have both a modded VINDRIKTNING and the airgradient, imo the airgradient is worth it if you want everything in one package. More accurate than the ikea, a nice screen/case, and you don’t have to strap a humidity sensor to the outside. Plus CO2 is great, more people need CO2 detectors.
Did just that by following that particular tutorial. Didn't expect accuracy, just following how air quality changes when baking, turning on humidifier, etc.
However now my VINDRIKTNING shows red with MAX reading all the time - I suppose not to be placed in the kitchen - some sticky oil grease landed on the sensor.
Wish I had seen this before I bought all the constituent parts on sparkfun! Though I do have some concerns about the accuracy of the PM2.5 sensor (mainly because the data sheet isn't exceptionally clear).I ended up getting the Sensirion equivalent over this one even though its quite pricey.
Every all-in-one air quality monitor I've seen except one omit some fairly important metrics - NO2 and hydrogen sulfides. I'm guessing it's because the sensors are extremely expensive (I got quotes for $90+/ea from one vendor). I ended up finding a startup, SPEC Sensors, that has much cheaper screen-printed sensors, and if their data sheets are to be believed, they're more than sufficient.
I bought one of the DIY Pro kits and put it together. I liked it overall. I think the kit is a good value, it's convenient to get everything all together, and the injection molded case is nice. The included software and cloud dashboard are convenient and functional. There are some less good parts, though:
- The instructions aren't great, but I can't remember what I had trouble with specifically.
- The included screws for the case are tiny, soft, and aren't self tapping. I never got them in all the way and gave up on them after the first disassembly. The USB power cable sort-of holds the clamshell together without them.
- I had issues with the reliability of the connection to the I2C sensors, especially after adding the SGP30. Reducing the speed to 100kHz helped somewhat but made the display update slowly. I never got the SHT3x temperature sensor to work reliably in the bottom corner position, so I moved it to the open top spot. I did try out various levels of I2C pull-up and removed redundant pull-ups from the modules that came with them installed. I think part of the problem is the loose fit of the included pin headers, soldering the sensors directly may help.
- The temperature sensor always reads high by about 5-10 degrees F, even when installed in the recommended far corner position. I tried mounting the airgradient vertically to try to induce a draft to clear out the generated heat but that didn't help. I could try to calibrate it but I doubt it's a simple offset.
- The dashboard is basic, had some annoying bugs, and they want you to pay for it. I can't remember specifically what I disliked because I replaced the firmware with EspHome long ago and set up a grafana dashboard to monitor it.
No matter how much they wish it were otherwise, OSI doesn't get to dictate what "open source" means. It's not their trademark. The term existed before they did. And equally as importantly, the words open and source existed before they did.
The source for AirGradient is not closed. It is open.
This is tangential, but is anyone aware of a live outdoor CO2 levels map? I've never been able to find one anywhere.
Because outdoor levels seem to vary significantly in a kind of 400-600 range, and it's impossible to calibrate a sensor outside without a reference point. On a windy winter day you can probably assume it's close to the global ~414, but on a muggy still summer day my sensors usually read significantly higher when holding them outdoors.
If you're like me and only looking for CO2 monitor, here is a short story.
I was researching all the sensors and kits and was narrowing down on AirGradient actually. Per my research the best last gen CO2 sensors are from swiss Sensirion SCD4x series. So I started looking how to build something on it etc.
While poking around, by pure chance I saw that Sensirion makes SCD4x-CO2-Gadget which is SCD41 sensor with LED indicator and BLE and powered by USB the size of flash drive.
So, you can just stick it in USB charger anywhere and either use visuals or a mobile app that will show the number or import data for a chart.
All for $60 from official Sensirion dealer like digikey.
I don't mean to sound like an Ad, but it's the best sensor as far as I know, for least cost and nothing to solder (perhaps a negative for some :)
No affiliation.
This is indeed the absolute best value co2 consumer 24/7 monitor you can buy right now.
You don't have control over calibration however, it's set to auto. So you need to expose it to outside air every 7 days or it will drift. The good news that a drift should be automatically fixed in just a few minutes after you take it outside.
If you live in a high co2 area, the ppm values will not be accurate. But relative measurements will be. And you can just add the difference if you know it to any number you see.
I ordered two DIY pro kits (with the TVOC sensors) earlier this month and went to start working on them yesterday. After flashing the firmware, neither one would create a hotspot for me to connect to. Looking at them and doing some googling, i found they include knock-off Wemos D1 minis (labeled "mimi"). It looks like they're aware there are Wi-Fi issues, but the chips are still being used [0][1]. I sent in an email yesterday but I'm not expecting a response until at least tomorrow.
Each time I see these, I feel a bit weird because they all rely upon a specific sensor, and the software / electronics is barely above beginner level.
A PM2.5 sensor is based off of infrared LEDs and photodiodes.
CO2 however is harder for me to understand. Does anyone know how that works?
Temperature is easy: just a calibrated thermistor.
Humidity: I dunno and am also curious.
--------
It's be a lot more comfortable for me to call this open source if the sensors actually gave design control to the engineer, more so than just assembly.
The Senseair S8 CO₂ sensor[0] used in this project also uses an infrared LED and works on the principal that CO₂ absorbs certain frequencies of light.
So if you know the brightness of the LED and the volume of air between it and the sensor, you can calculate the amount of CO₂ by comparing the expected vs. received light intensity.
We also offer a fully certified commercial product (AirGradient ONE) focusing on B2B (Offices, Schools). Then you have monitors from other companies e.g. Awair, AirThings, Kaiterra, Air Visual etc measuring similar air quality parameters.
We try to set us apart by promoting open data standards, clear data ownership, long lasting products that are easy to repair and maintain. More details on our main website [1].
Well we do a version with multiple uplink technology option and a full SDK[1]. The market is actually quite segmented depending on the final use case. This is IMO mostly because of the price of these devices. The CO2 probe itself is costly especially if metrologically calibrated so if you want one for every room in the school / office / home its not insignificant investment.
I'll include a link to our datasheet [1] as to actually answer the question hoping Im not breaking HN rules.
I struggled with the same search and ended up getting the AirGradient DIY Pro Kit Pre-Soldered. Not quite plug and play but the steps to get it up and running are fairly straightforward. Just plug parts in, drop some firmware on, and go. Curious what other suggestions are out there because I would still like something simpler!
I have a handheld $65 TVOC meter, but it's tricky to get repeatable measurements. It needs 5-10 minutes to warm up, but then the reading jump around almost 2x. It has 4 digits of resolution, but 1 digit of accuracy?
Regardless, indoor TVOC levels increase significantly over 2-3 days. Then opening the windows brings them back down. Not sure if that's normal. (TVOC = Total volatile organic compounds)
Compared to CO2 and PM measurements, TVOCs are the most difficult to measure because they encompass a wide range of chemicals that trigger the sensor. Some are very harmful, e.g. aggressive paint and others (hopefully) harmless like sunscreen. Both trigger the sensor.
Additionally the sensors are only showing you correct absolute levels in lab conditions, e.g. using ethanol at a specific temperature and humidity. So in real environments, the absolute values are pretty useless.
We now use a newer generation of TVOC senor e.g. the SGP41 that is more index based and eliminates the issue of the absolute values.
We also observe that temperature and humidity can influence the TVOC measurements.
All in all, TVOC is good to detect spikes and check what is causing these, e.g. use of aggressive cleaning chemicals. However the absolute levels in e.g. ppb should better be ignored.
Yes, it is normal that fresh air flushes out chemicals and you can see this improvement. We do like the SGP4x series from Sensirion for TVOC sensors.
FWIW, TVOCs can collect together and move around in "waves", your indoor air is not just one big evenly distributed "soup". The sensors also have lots of factors that affect them, such as humidity - you can usually find more info in the docs for the sensor part.
A better approach would be to sample consistently and use that to build a graph showing TVOC ppm over time.
Looks like you can get a PoE to USB-C adapter for $35:
Revotech PoE to Type-C Adapter Converter, Convert POE to Output 5V/2.4A USB C with Ethernet, IEEE802.3af with 10/100Mbps , Wired Broadband and PD Charging for Smart Phone/Tablet, Plug and Play (P2C5V) https://a.co/d/7320MNa
Wonder how complex it is to access the network this way. If you have to modify the USB implementation you may as well skip the adapter and add an RJ45 + internal PoE chip…
We made a small co2 sensor based on the sensirion scd30 and m5 stack. If you want a portable sensor with battery and display, you might be interested. Source code is on https://github.com/smoca-ag/m5stack_co2_sensor
[+] [-] pppone|3 years ago|reply
[1]: https://www.aqmd.gov/aq-spec/sensors
[2]: https://www.open-seneca.org/
[3]: https://sensirion.com/products/catalog/SPS30/
[4]: https://community.purpleair.com/t/new-version-of-plantower-p...
[+] [-] NikolaNovak|3 years ago|reply
Every review I check for any consumer accessible device seems to indicate they're inaccurate, miscalibrated, or downright deceptive :-(
[+] [-] daniel_iversen|3 years ago|reply
[1] https://getuhoo.com/
[+] [-] tomaskafka|3 years ago|reply
[+] [-] karmelapple|3 years ago|reply
https://a.co/d/9o1Qvzb
[+] [-] LeegleechN|3 years ago|reply
[+] [-] blueblimp|3 years ago|reply
On the topic of allergens, I wasn't able to find any device that can measure that.
[+] [-] ahaucnx|3 years ago|reply
You can check if the monitor is RESET AIR certified which is an independent and 3rd party test against reference devices.
https://www.reset.build/directory/monitors/air
[+] [-] dewey|3 years ago|reply
[1] https://www.notebookcheck.net/IKEA-VINDSTYRKA-smart-air-qual...
[+] [-] harrydehal|3 years ago|reply
https://map.purpleair.com/?mylocation
https://www2.purpleair.com/products/list
[+] [-] dotancohen|3 years ago|reply
https://www.aliexpress.com/item/1005005011458177.html
$15 from AliExpress including shipping. If you are concerned about accuracy, could you not take it outdoors to see how it measures the unaffected atmosphere, then bring it back indoors to see how it compares? For instance, if you are concerned that the 900 PPM reading in your bedroom is inaccurate, you could take it outside and see how it reads compared to the expected ~420 PPM. You might be off by a few PPM, but would it not be accurate enough to see if you are approaching dangerous levels?
[+] [-] rogers18445|3 years ago|reply
It does use auto calibration, which means you need to bring it outside for a few minutes every once in a while (7 days IIRC). Not doing it will not break it, but the readings will drift downward (sensor assumes that the lowest reading it gets in a period of time must be 400 ppm) - and will be fixed in a few minutes outside (few minutes of <400 ppm sets lowest reading to 400).
[+] [-] aedocw|3 years ago|reply
[1]: https://style.oversubstance.net/2021/08/diy-use-an-ikea-vind...
[+] [-] M3L0NM4N|3 years ago|reply
[+] [-] PaulBGD_|3 years ago|reply
[+] [-] jve|3 years ago|reply
However now my VINDRIKTNING shows red with MAX reading all the time - I suppose not to be placed in the kitchen - some sticky oil grease landed on the sensor.
[+] [-] unknown|3 years ago|reply
[deleted]
[+] [-] kayson|3 years ago|reply
Every all-in-one air quality monitor I've seen except one omit some fairly important metrics - NO2 and hydrogen sulfides. I'm guessing it's because the sensors are extremely expensive (I got quotes for $90+/ea from one vendor). I ended up finding a startup, SPEC Sensors, that has much cheaper screen-printed sensors, and if their data sheets are to be believed, they're more than sufficient.
[+] [-] mastax|3 years ago|reply
- The instructions aren't great, but I can't remember what I had trouble with specifically.
- The included screws for the case are tiny, soft, and aren't self tapping. I never got them in all the way and gave up on them after the first disassembly. The USB power cable sort-of holds the clamshell together without them.
- I had issues with the reliability of the connection to the I2C sensors, especially after adding the SGP30. Reducing the speed to 100kHz helped somewhat but made the display update slowly. I never got the SHT3x temperature sensor to work reliably in the bottom corner position, so I moved it to the open top spot. I did try out various levels of I2C pull-up and removed redundant pull-ups from the modules that came with them installed. I think part of the problem is the loose fit of the included pin headers, soldering the sensors directly may help.
- The temperature sensor always reads high by about 5-10 degrees F, even when installed in the recommended far corner position. I tried mounting the airgradient vertically to try to induce a draft to clear out the generated heat but that didn't help. I could try to calibrate it but I doubt it's a simple offset.
- The dashboard is basic, had some annoying bugs, and they want you to pay for it. I can't remember specifically what I disliked because I replaced the firmware with EspHome long ago and set up a grafana dashboard to monitor it.
[+] [-] ahaucnx|3 years ago|reply
It has also pin breakouts so you can easily add additional sensors if required. Hardware and software are both open source and can easily be adjusted.
[+] [-] RobotToaster|3 years ago|reply
https://www.oshwa.org/faq/#non-commercial
https://opensource.org/osd
[+] [-] simondotau|3 years ago|reply
The source for AirGradient is not closed. It is open.
[+] [-] crazygringo|3 years ago|reply
Because outdoor levels seem to vary significantly in a kind of 400-600 range, and it's impossible to calibrate a sensor outside without a reference point. On a windy winter day you can probably assume it's close to the global ~414, but on a muggy still summer day my sensors usually read significantly higher when holding them outdoors.
[+] [-] hrez|3 years ago|reply
I was researching all the sensors and kits and was narrowing down on AirGradient actually. Per my research the best last gen CO2 sensors are from swiss Sensirion SCD4x series. So I started looking how to build something on it etc.
While poking around, by pure chance I saw that Sensirion makes SCD4x-CO2-Gadget which is SCD41 sensor with LED indicator and BLE and powered by USB the size of flash drive.
https://sensirion.com/products/catalog/SCD4x-CO2-Gadget/
So, you can just stick it in USB charger anywhere and either use visuals or a mobile app that will show the number or import data for a chart. All for $60 from official Sensirion dealer like digikey.
I don't mean to sound like an Ad, but it's the best sensor as far as I know, for least cost and nothing to solder (perhaps a negative for some :) No affiliation.
[+] [-] rogers18445|3 years ago|reply
You don't have control over calibration however, it's set to auto. So you need to expose it to outside air every 7 days or it will drift. The good news that a drift should be automatically fixed in just a few minutes after you take it outside.
If you live in a high co2 area, the ppm values will not be accurate. But relative measurements will be. And you can just add the difference if you know it to any number you see.
[+] [-] sc00ty|3 years ago|reply
[0]: https://www.airgradient.com/open-airgradient/blog/d1-mimi/
[1]: https://forum.airgradient.com/t/issues-with-new-dyi-pro-pres...
[+] [-] ahaucnx|3 years ago|reply
The "Mimi" version should not have the problem and we found it to be very stable and it is currently our default version.
More information here: https://www.airgradient.com/open-airgradient/blog/d1-mimi/
[+] [-] miniwark|3 years ago|reply
https://smartcitizen.me/
https://www.seeedstudio.com/Smart-Citizen-Starter-Kit-p-2865...
It is mainly for outdoor pollution (including light & noise), but it also include indoor gaz sensors for Co2 and VOC.
[+] [-] dragontamer|3 years ago|reply
A PM2.5 sensor is based off of infrared LEDs and photodiodes.
CO2 however is harder for me to understand. Does anyone know how that works?
Temperature is easy: just a calibrated thermistor.
Humidity: I dunno and am also curious.
--------
It's be a lot more comfortable for me to call this open source if the sensors actually gave design control to the engineer, more so than just assembly.
[+] [-] breput|3 years ago|reply
So if you know the brightness of the LED and the volume of air between it and the sensor, you can calculate the amount of CO₂ by comparing the expected vs. received light intensity.
[0] https://rmtplusstoragesenseair.blob.core.windows.net/docs/pu...
[+] [-] aidenn0|3 years ago|reply
If you don't know what you're doing, then you'll get it wrong (except maybe if you use a fan).
[+] [-] edge17|3 years ago|reply
[+] [-] ahaucnx|3 years ago|reply
We try to set us apart by promoting open data standards, clear data ownership, long lasting products that are easy to repair and maintain. More details on our main website [1].
[1] https://www.airgradient.com/
[+] [-] marcel_hecko|3 years ago|reply
I'll include a link to our datasheet [1] as to actually answer the question hoping Im not breaking HN rules.
[1] https://docs.moirelabs.com/scoria-datasheet/
[+] [-] wallflower|3 years ago|reply
https://www.iqair.com/us/air-quality-monitors
https://www.purpleair.com
[+] [-] zokier|3 years ago|reply
[+] [-] pigtailgirl|3 years ago|reply
[+] [-] unclekev|3 years ago|reply
[+] [-] davidrhunt|3 years ago|reply
https://www.airgradient.com/open-airgradient/shop/#!/DIY-Pro...
[+] [-] sunsetMurk|3 years ago|reply
1- https://smile.amazon.com/gp/product/B08L73QL1V 2- https://www.home-assistant.io/integrations/vesync/
[+] [-] Tempest1981|3 years ago|reply
Regardless, indoor TVOC levels increase significantly over 2-3 days. Then opening the windows brings them back down. Not sure if that's normal. (TVOC = Total volatile organic compounds)
Any recommendations for quality sensors?
[+] [-] ahaucnx|3 years ago|reply
Additionally the sensors are only showing you correct absolute levels in lab conditions, e.g. using ethanol at a specific temperature and humidity. So in real environments, the absolute values are pretty useless.
We now use a newer generation of TVOC senor e.g. the SGP41 that is more index based and eliminates the issue of the absolute values.
We also observe that temperature and humidity can influence the TVOC measurements.
All in all, TVOC is good to detect spikes and check what is causing these, e.g. use of aggressive cleaning chemicals. However the absolute levels in e.g. ppb should better be ignored.
Yes, it is normal that fresh air flushes out chemicals and you can see this improvement. We do like the SGP4x series from Sensirion for TVOC sensors.
[+] [-] parker_mountain|3 years ago|reply
A better approach would be to sample consistently and use that to build a graph showing TVOC ppm over time.
[+] [-] pbronez|3 years ago|reply
TI has PoE chips for around $4, but I don’t know enough about electrical engineering to figure out how to swap that into this design.
https://www.ti.com/product/TPS23861
[+] [-] pbronez|3 years ago|reply
Revotech PoE to Type-C Adapter Converter, Convert POE to Output 5V/2.4A USB C with Ethernet, IEEE802.3af with 10/100Mbps , Wired Broadband and PD Charging for Smart Phone/Tablet, Plug and Play (P2C5V) https://a.co/d/7320MNa
Wonder how complex it is to access the network this way. If you have to modify the USB implementation you may as well skip the adapter and add an RJ45 + internal PoE chip…
[+] [-] pfyy|3 years ago|reply
[+] [-] patja|3 years ago|reply
https://www.printables.com/model/121265-salud-co2-monitor
[+] [-] jph|3 years ago|reply
I do see your commercial offering (AirGradient ONE) and I'd like to buy that for my office. How does a typical consumer purchase one online?
[+] [-] upon_drumhead|3 years ago|reply
https://www.airgradient.com/open-airgradient/shop/