Actually, the reason CO2 sensors are used for air quality monitoring instead of oxygen sensors has nothing to do with cost, energy usage, size or how complicated they are (though they are costly). It's because we're not interested in oxygen levels, as it's very difficult to lower the oxygen levels to any appreciable level unless a room is sealed with a lot of people, but CO2 itself is toxic in high concentrations, and it can produce dizziness, feeling tired, and other related symptoms, starting from 1000-2000 ppm (that's only 0.1-0.2 %! At those levels oxygen concentration would, at most, fall from 21 % to 20.8-20.9 %, not near enough for any appreciable effect). Here's a link to a Tom Scott video about that if you want to learn more: kzfaq.info/get/bejne/Z7SYktmp1d_HdXU.html.

CO2 levels can go up to 7000 ppm in submarines and space capsules. These levels are tolerable, but the CO2 level is an easily measured proxy for the usually accompanying high levels of VOCs and other air contaminants . We once measured CO2 levels in a crowded art studio. The air was stuffy and oppressive. Levels were 4500 ppm. The room needed more ventilation. I have also measured levels outside when many trees were photosynthesizing. They were just above 300. "Ah, fresh air!" They can get even lower during the day in a growing cornfield. And, your breath might be 40,000 ppm!

yes just like you say - one of the new buildings where I worked had a CO2 sensor which was supposed to open up outside air dampers to bring in more air. But while the engineers had specified it and the controls company installed it - but they never calibrated it or made sure that it worked properly. So it did not really ever do anything useful. I was on maintenance but that was not my building and we were all just getting up to speed on how the new DDC HVAC systems were supposed to work and also too busy fixing the most blatant screw ups that the controls company left for us. No they never had anyone commission the buildings which did seem really stupid for multi- million dollar buildings. I wish I had seen your video many years ago so I could have fixed that CO2 sensor issue !

Thank you very much Andreas Spiess for this great measuring CO2 tutorial and for evaluating our environmental sensors SGP30 and SCD30.

Just wanted to reach out and say thank you for the content you are producing. The quality is excellent. You are structured and follow a clear logic in your presentations. Great overall! Keep it up!

Incredible presentation ,as an Environmental Engineer who works with these types of sensors and many others I am highly impressed of your depth of knowledge in this field. Kudos !! you never cease to amaze me you have an incredible grasp of so many fields .

Again, another useful video and again you have helped me unknowingly with an unconnected project. Please keep up the good work.

The school of my son has a CO2 meter with colored LEDs in every classroom.

Nice coincidence, jist yesterday I started trying out a VOC sensor to make a "fart detector", planned be used to identify when our cat uses the toilet.

As a German living in Sweden I have to point out that SENSEAIR is a Swedish company. I have recently been involved with them as being an opponent in a thesis defense which deals with the improvement of both their CO2 and CH4 sensors.

Thanks for yet another great video. I have been using the MH-Z19B in exactly this way, to alert when I need to ventilate the room. Has been working for over 2 years now without any problems. However I was not able to make it work on 3.3V, only on 5V. Second thing - i needed to turn off the correction (ABC) - otherwise the values would drift off considerably with time, especially if windows are rarely opened in winter. The SCD40 looks very interesting. Would like to try it out as well, I guess it should also have a reasonable power consumption to use it in battery powered device. Then you can even carry it with you everywhere))

Nice video. You are an inspiration. I just used senserion TVOC and senserion CO2 sensor a couple weeks ago. I actually used your node-red videos as reference. Thanks alot for that btw. Anyways what was shocking for me where the tvoc readings when I 3D printed. They where off the charts, and and for sure not healthy.

It is shocking to see the difference in background CO2 in 6 years from 2018 to 2024. NIWA Baring Head in NZ is 421.5ppm today and Mauna Loa Hawaii is 427.5ppm. So it is likely that the new 2024 calibration point should be around 430ppm for the Northern Hemisphere and 420ppm for the Southern Hemisphere. Your video is , still, extremely helpful. Far more than any other on KZfaq, even recently, related to these inexpensive IAQ sensors. My very cheap (

I did a lot research on Voc sensors. Voc (mox) sensor are heavily influenced by humidity amongst other factors. That's why your sgp30 shows that high value during the night. Even very low changes in humitdy counts for some 100ppm voc. I'm not aware of any single implementation that is able produce values usable over a period for days or weeks. Yes, they respond to changes very good but not on a absolute level. Co2 (mhz19b) must be the primary indicator.

As always, nice no BS explanation. I hope in the next video you also explain the best sensor/method to measure air quality on workshop environment. Like source from solder fume, glue gun, 3d filament, etc. Can't wait!!!

Nice to see that I‘m not alone to point out CO2 monitoring in schools! At the school of my kids I‘ve implemented a project making CO2 traffic light using MHZ19B sensors and RGB LED. After making some prototypes the teachers took over the idea and they made some enhancements as part of a junior academy project. I think I planted something...😀

Do the same video for fine particles sensors

hahah i have to laught everytime is see the little hand :D (+1 for the cat)

@ 17:00 "[ ...] without oxygen the fire stops. Problem solved without collateral damage." As long as there are no humans in the same room. Else there will be a lot of collateral damage!

You just read my mind! I just built one of these! With the MH Z19B.

I have to say I like your presentations. A handy video, like most of yours are - I'll have to check out the Raspberry Pi series again! Thanks for doing these :)

i have a sharp air purifier that triggers the fan whenever i fart. it also gets triggered by alcohol fumes, like in anti-bacterial hand wash. it must be almost 10 years old now but the sensor is still very sensitive to changes in the air

You are a genius sir, that is a fantastic idea!

I have been using the Winsen for some time already in a greenhouse. Very reliable

This episode should be a high school homework assignment.

Perfect timing. I just hooked up my first MHZ19B 2-3 days ago. Sometimes i get massive co2 value drops that i can't really explain. Like in the middle of the night without opening a window or door. One drop could be the automatic 24h calibration, but the other ones confuse me a little bit. One problem could be that it's still on my breadboard powered by the 5V pin of a D1 Mini, another one could be that 2-3 days are just not enough time to be fully calibrated. But so far it does a much better job than the CCS811 eCO2 i tried a few months ago. Maybe those TVOC Sensors like the SGP30 / CCS811 could be useful for a hobby room with all kinds of gases / particles.

You are a legend professor!

Bananas emit ethylene gas. This is why they can be picked before they are ripe and then ripened in stores that circulate the ethylene which helps the ripening process. My wife places unripe pears next to the bananas to help the pears to ripen. Bob

After a long weekend of drinking, I have many toxic gasses in my apartment.

The reason lambda sensors are not used indoors, is because they need to be quite hot too work. Around 300 to 600°C hot. Inside the exhaust of an engine this is not too big an issue, but in open air it would take quite a bit of power

Very nice again! I need to make mine soon, since my hobby rooms are all in the basement! Thank you again Andreas!

Great material! It is a good thing to always seat in front row

Great video. And more relevant than ever as right now in Germany we'll start to have a "venting" intiative at schools during Corona pandemic.

Automotive O2 sensors will only work at high temperatures, not room temperature. Some O2 sensors have built in heaters or rely on the vehicle to heat the sensor as it warms up. The vehicle engine and ECU can run without the O2 sensor, this is called OPEN LOOP when cold. When the engine and O2 is heated, the ECU then runs using the O2 sensor reading, CLOSED LOOP operation.

Nice coincidence There was a "zukunftstag" at ETH Zurich two weeks ago. We have built CO2 measuring boxes with kids. At the end they could take them home and place them in their classroom now they know when to let some fresh air in.

Andreas! Nicely documented and explained.

You absolutely forgot about the ccs811. It's really cool and chip sensor with low power mode.

Another fantastic project and video! Thanks!

CO2 levels in outdoor air vary considerably over the day and between seasons. They also vary substantially between locations, even at the same altitude. Using a global average is like using the average of telephone numbers to call somebody. CO2 gas presence is a sign of life... Essential for the carbon cycle that sustains our lives. When CO2 levels decline below about 180ppm, plant life struggles. You could hike up to the treeline on a nearby mountain and calibrate your sensor to a baseline of about 200ppm during daylight hours. CO2 levels can be higher at night due to decomposition of biomass and a slight increase in air pressure... But without sunlight, the higher CO2 is of no use to plants. Exhaled breath contains about 40000ppm ... sometimes higher. If your readings are substantially lower then it's likely that the sensor is wrong. P.S. drowsiness at University lectures was more closely correlated to the acoustic emissions at the front of the theatre than ambient CO2 levels 😀

Congratulations from Brazil. Here is the guy with brazilian accent.

I deployed MHZ19B and it works like a charm with ESP32 It did not change my life but I am opening the window more often - bills for heating will go up during winter ;-) Btw after researching available sensors I am happy I decided to go for this one - it gives nice and stable readings - going to sleep with 400ppm and in the morning it is 1500 - hmm, now I understand why sometimes I wake up more tired than I went to sleep

I think the major problem with lambda sensors is the high operating temperature required (300° to 600° C). I've been in pretty hot meeting rooms before but even this is a bit much.

As always Andreas does great videos.

Always very interesting video, thank you very much !

Very good and helpful video 👍

Please do a comparison with CO sensors too and possibly PM/dust sensors

I am back in school later in life and I agree that we need sensors in each classroom. I always thought there was a reason such as this that you get exhausted after 50 minutes in a class.

Very interesting. Thanks for sharing !

@17:21 your breath is lethal! ;-) This is a good reason for such a device. In my experience teachers can be extremely boring, and having a poor environment for your brain doesn't help.

I'm glad you used these higher quality sensors. The MQ-x sensors that come with the starter kits are relatively useless. I just finished taking 120,000 readings of my lab and your video has given me some great information of things I need to check. Thanks for all you do.

Hydrofluorocarbon is used for fire suppression in most data centres. The gas cylinders are smaller compared to CO2, and safer for people to return.

Hi Andreas! Do you know the CCS811 VOC sensor? It's the most popular on AliExpress. I've been using it for a while and it is pretty accurate. By the way I have a question, do the sensors you showed need a burn-in for accuracy? Hot plate ones often need a 48hr burn in

Great video! I would be very interested if you can measure co2 or voc (or air particles?) increase while running your 3d printer. Especially PLA/PETG/ABS which we home-makers can use. Anectdotally I‘ve sometimes felt the „meeting effect“ in the beginning when I had the printer stationed in my bedroom.

Who doesn‘t feel tired in meetings?

it's really goooood video. Is it ok for output cycle faster and , how to check the fastest rate? i want to see more detail graph

Exactly what I was looking for! Thanks!

This is similar to my first ESP32 project, an atmospheric monitor/logger that measured particulate and combustible gas concentration with a Shinyei PPD42NS and an MQ-2 sensor. It uses GPS for a reference time signal and a BME280 sensor for reference pressure, temperature, and humidity values. I looked into MQTT communications but got distracted by trying to estimate power requirements (was hoping to add solar panels and battery). The particulate sensor uses a resistor as a heating element to move air and particles past the IR sensor and I believe that dominated the power consumption. Search for apthorpe/aerosniff on BitBucket for the code and Fritzing schematic & circuit diagram if you're interested. Thanks for making ESP32 development so accessible; I wouldn't have been able to do that project without your videos :)

The little hand @7:01 😆

I bought a set of 9 cheap gas sensors a while back but just got around to trying them now. It was my first ESP32 project using more than one ADC input, so I was very surprised and disappointed to find out that if you use WiFi on the ESP32, half the ADC inputs are disabled, and in the case of my DOIT ESP32 DEVKIT V1's, the ADC pins labelled VN and VP also don't work, so I was left with 4 usable ADC pins. I'm considering disabling WiFi, and using Serial Comms to get an ESP32 to use an ESSP8266 to do the WiFi comms to my Node.Red server. Or I could just use 2 ESP32's to handle 8 sensors.

Thanks for the informative video, just what I needed right now. :-) I’m working on a MQ135 VOC sensor and Sharp infrared dust sensor project. The MQ135 fluctuates a bit in it’s output values so I guess it’s best for short term relative measurements. My program periodically adjusts the “zero” value to compensate.

wow, that chinese CO2 sensor finally is an affordable CO2 sensor. I've been waiting for something like that for ages.

Great video and look forward to the update particularly how the eCO2 correlate with CO2 readings on extended runs. I currently use a CCS811 for eCO2 and plan to test the SGP30 for similar reasons. Also not sure if I missed but did you send humidity compensation values into the SGP30? Per the datasheet this affects both eCO2 and tVOC reading

A thing to keep in mind. If it's only about how people feel, measuring CO2 is is right way. Higher CO2 concentrations are what makes us feel bad. But it's not a good indication on wether or not the environment is suitable for you, or healthy. That's a "fun" thing about humans. We indicate if we are suffocating from oxygen depletion by measuring CO2 concentration. You can easily suffocate without noticing if the oxygen get's replaced by something different than carbon dioxide

In case you get the SCD30 - I made a couple of packages to get it running on a Raspberry Pi in Node.js, Node-RED, and a CLI: * www.npmjs.com/package/scd30-node - Node.js TypeScript API * www.npmjs.com/package/scd30-cli - CLI * www.npmjs.com/package/node-red-contrib-scd30 - Node-RED node Thought some of y'all might find this useful.

As always amazing video master Andreas. I think I will try it in my university classroom, because boy in Physics class we are always tired, I am 100% sure it is not because of the boring subjects but because of the high CO2 concentration. I am curious to try multiple VOC sensor, I will try with the bosch BME680 and SGP30, because CO2 is still above my maker budget. Again thanks for the amazing video!

The Lambda sensor actually compares the oxigen levels between the exhaust and the outside

Andreas, Thank you performing the tests that I would otherwise have had to perform myself! By the way, if you want an excellent supply of CO2, you could try Dry Ice, which is nothing but frozen CO2. I believe you can get it from grocery stores, or perhaps from ice cream suppliers. Stay safe!

Very informative and interesting video. Thank you!

A steady diet of beans and cabbage is very healthy and prevents unnecessary meetings.

this was my internship project

thanks for the video

Thanks for the great video Andreas. Any idea how "exposed" the sensor needs to be to read accurately? I'd like to add one to my camper which is a small enclosed space, but I'd likely put it in a small project box in a cabinet or out of site location. Would you think the detector would be useful if it's not out in the open, especially since you mentioned CO2 drops down below air?

Did not expect the wet cat video.

Impressive review/update Thanks for sharing👍😀

Heads up for Raspberry Pi users concerning the SCD30 as it mentions I2C Clock Stretching in its documentation which could be a problem for Raspberry Pi users who want to use the SCD30 I2C interface, so you might have to use one of the other SCD30 interfaces with a Pi. Andreas perhaps a good video topic would be I2C clock stretching and the Raspberry Pi.

lambda sensors on cars only work accurately at high temperature

Is that a Surface tablet? They seem to be cool but pricey... Is it worth it?

Can you please test also Scd41 sensor and exploriR-M sensor in humidity environment ?It is a good test..

We started a project in our school with a small co2 "traffic light" on an e-ink display. We are on our way to setup one sensor (with temp and hum) in every room and show the data in Grafana on a monitor in every floor. The VDE gave us 2000€ for this project. If you are interested in, contact me.

Ein gutes Schul-Projekt: bei der meist gegebenen Weitläufigkeit wäre Kommunikation über LoRaWAN angebracht.

This topic is on the agenda now! I will build one for my school. Which sensor should I buy now?

I'd like to see one on the PMS5003 if you feel like doing it, it's a really solid PM2.5 sensor

@andreas spiess I am a biology teacher. And yes air quality is important for staying focused. Would be interesting to build with students. I prefer blynk platform to read data since students can easily work with that. I already have nodemcu + supplies, just need to order the sensor.

16:30 could you use a can of soft drink or sparkling water to obtain the CO2?

thanks ,clear demonstration

A nox sensor would be useful to detect the dirty air in cities. Especially in the cold season, there are inversion weather conditions. Poison gases accumulate on the ground, so that it stinks terrible, so you better keep the window closed. Btw. LPG does not release nox and costs less than half its consumption.

I am an absolut Beginner in electronics. I have to implement a MiCS-2714 or something similar in our weather-sensor. So i searched for it on KZfaq and found you. It's funny, that we live not even 10km apart. Now I have a huge problem with the Sensor. I do not have your Cat for the calibration process. Could you please tell her to come over, cause I'm pretty lost with this topic. Sensors and I2C ADCs and so on, not my world.

Couldn't you calibrate by spraying some nitrogen across the sensor for a few minutes until it reads 0ppm?

I would think measuring oxygen levels would be a good idea. Perhaps as a control. If O2 levels are low I would think that would have an effect on CO2 and other gases being.measured. Low 02 means there is a not a good supply of good air coming into a room. A question of why would almost beg for an O2 sensor as well.

Plant more indoor plants to compensate these gas in your work place and see the difference.

That other sensor you showed is not a German company, but a Swedish company SenseAir. The sensor you show is the S11, or Sunrise sensor. You can see the source code to make it working here: github.com/letscontrolit/ESPEasy/blob/mega/src/_P052_SenseAir.ino It supports both the S8 and the S11. The S11 can also be set to I2C using some resistors, so maybe you had it wired incorrectly? About the "calibration" of the sensors. Please keep in mind you need to have the sensor placed in a well ventilated room (not outside) to determine the 400 ppm level. You want to make sure it is in the same conditions as when you use it (room temperature and humidity) and also make sure there is no direct sunlight on the sensor or placed near a source of IR light like a heater.

Great video thank you. If i wanted to monitor air quality in my living room with a log burner, would these sensors work please?

I'm a big fan from east switzerland. I just bought a sensirion scd30 and would like to battery operate it. I planed to frequently switch them on with a TPL5110 Nano Power Timer to measure at an interval of 1 min, send the result to an mqtt server and then power off for the next minute. Do you have any suggestion why this could be a bad idea?

Leider schaffe ich es nicht das MH-Z19 Arduino-Sketch zu kompilieren. Ich habe das Modul "FreeRTOS" installiert, aber Arduino meldet trotzdem "MH-Z19:11:31: error: freertos/FreeRTOS.h: No such file or directory". Wie wurde der Sensor an den ESP8266 angeschlossen? Merci!

How did you know I had problems with my sensor. CCS811 now I know thanks

Excelente trabalho

Why do you save your MQTT messages in InfluxDB through NodeRed? You can install Telegraf along with InfluxDB and automatically save all your MQTT messages (or just some topics) in the InfluxDB Database.

Great project, I am also using an SGP30 to measure eCO2. Your values are much smoother than mine. I think my calibration did not go as well- I simply let it run for 12 hours which is what I thought the documentation outlined. What calibration steps did you take to get this good data output?

Great job as always !!! thanks! Can you recommend a specific sensor-not too expensive- to study photosynthesis? If i get it wright eCO2 sensors are excluded.

Wonderful!