This is the first in a series of articles on using CO2 devices to monitor ventilation indoors and a look at several DIY projects for building these devices. As the pandemic began, we covered the maker’s civic response in a series of articles and videos that we called Plan C. As we now expect a gradual return to normal activity, approaching an end of the pandemic, we call this new series Plan CO2 — how we might get back together safely.
Plan C02 LIVE: Join us on Friday, April 23rd for discussion and demonstrations of CO2 device monitoring. Show us what you’re working on or learn how to get started. Register here for this live Zoom session at 12pm PDT / 3pm EDT on April 23.
A lot of students are now beginning to go back to the classroom, but few are equipped like Odessa Schulz, an eleven year old living in Montreal Quebec. When her school re-opened after the New Year break, Odessa carried with her a homemade electronic device that her father made that measured carbon dioxide (CO2) levels in the classroom and displayed it in parts per million (PPM).
After taking the reading, Odessa charted it on paper and brought it home. In the evening, Odessa and her father, Stephan Schulz, analyzed a chart of the day’s readings, which tracked the readings over time. Each night he re-charged the battery on the device and off Odessa went the next day with the device in her backpack.
You can see CO2 accumulate as students settled down in the classroom. You could tell when they went to lunch and came back. For Stephan, the CO2 monitoring device could tell him if the classroom was properly ventilated, which meant that windows and or doors were open if the readings were below 1000 ppm. In January and February in Quebec, keeping the windows open when it is -20 C/-4 F means that classrooms are cold. Students were wearing masks and hats in the classroom, @stephanschulz3 tweeted.
On February 5, the local TV news in Montreal carried a story about the Schulz family, the device that Stephan made and his daughter who brought it to school. Odessa told the reporter that the device “basically says how much CO2 is in the air — if it’s over a thousand, that’s not good because there’s not enough fresh air.” She explained that in the classroom the device is hanging from the wall and she could walk over and take a reading. Doing this made her feel safer. Jennifer Dorner, her mom, also felt better having data about the ventilation of her daughter’s classroom.
This news about the device he built, Stephan recalled, “really helped people realize that aerosol particles might be something worth looking into and be aware of.”
Unprepared to Go Back to School
Schools were busily disinfecting surfaces in the classroom and around the school because that’s what they’d normally do. Yet, the evidence around the coronavirus was that it spread through airborne particles, or aerosols. (The Diamond Princess Cruise Ship was, in effect, the experimental lab that demonstrated that the virus was spread through the ventilation system, not on contact.)
Stephan Schulz and Jennifer Dorner have two children, 11 and 12. “For the longest time, they went to school,” he said. “Then there was a period here in Quebec where they stayed home and recently they’re back. And it is with a sense of feeling uncomfortableness that we let them go back.”
Stephan recognized that his children needed to see their friends, “So it was worth the risk, I think,” he said. Still he was bothered by the government response to the pandemic. “It always seemed that the government, Canada and Quebec were very slow in basically incorporating what scientists have been saying for the longest time,” he added. First it was the mixed messaging around wearing masks, which didn’t make sense, so he and his family began making them at home and giving them to friends.
Stephan began by himself trying to learn about the science and make up his own mind about what was the best he could do for his family. He began thinking about monitoring aerosols indoors by measuring CO2.
Air quality sensors for outdoors measure CO2 and the base level measurement is around 400 ppm. Inside a classroom, if the room was properly ventilated, the CO2 levels of air inside would ideally match the air outside. If the windows and doors were closed in a classroom of 20-30, CO2 levels would rise, and higher levels can be used as a warning, indicating that there are more aerosols in the air. By monitoring CO2 indoors in a classroom, teachers and students can be reminded that they can decrease CO2 by simply opening windows and doors and leaving them open. The CO2 monitor makes visible these aerosols which are invisible.
Building a CO2 Device
“I’m a media artist by training,” said Stephan, who grew up in East Germany and came to Canada to get his Master of Fine Arts. “I do a lot of coding and software on a daily basis. Electronics like Adafruit and Sparkfun, and Tindie are very familiar to me.” He remarked that building devices by connecting components together is a “Lego-like system.” He decided he could build his own CO2 monitor.
“Arduino code is quite accessible for someone like me to make something like that, “ he said, adding that he always had an interest in science growing up. His favorite TV show was MacGyver.
In his research, he came upon the work of Guido Burger, a German maker and engineer living in southwestern Germany. Guido had developed and shared a project called “CO2 Ampel ” (ampel is a traffic light in German). The CO2 Ampel project (“Der CO2-Warner für die Schule”) had been published in the German edition of Make: Magazine in 2020 and also complete instructions were provided in German and English on a university website.
To monitor CO2, Guido used the SCD-30 CO2 sensor from Sensirion, a Swiss company. (There are other options.) This is an two-channel, optical sensor that uses two lasers to detect CO2 particles. At Adafruit, Stephan found the SCD-30 CO2 sensor mounted on a board that easily connects to an Adafruit Feather M4 Express. He added a battery and a small OLED display. It’s not a complex device but it isn’t cheap. Stephan said that the components cost him around $200.
His first version of the CO2 device displayed the reading but didn’t log data. That was what his daughter, Odessa, would do on paper. “It was actually quite a nice exercise for her to explain to her classmates and her teacher what she’s actually doing there and having to follow the scientific rigor of writing things down every 10 minutes,” he said. “I could see that when she was walking to school, the values went really low and then in school they went higher, but luckily they never went over a 1000 ppm,” he said.
Soon after, Stephan added an SD card so the device began writing the data from readings taken every 30 seconds. Graphing the data became easier, an automated task.
Monitoring CO2 in the Classroom
I asked Stephan if his daughter had any reservations about carrying this device into her school. “My children have been around media art for all their life,” he said. “They come to the installs and they know we solder at home once in a while. So she was totally into it.” You can see that Odessa got involved in making the device.
“She likes bringing new things to school and then having to explain to it to her teacher.” I also wondered about the school and its teachers being open to having such a device in the classroom. “We weren’t sure. Usually school isn’t very open to parents bringing in new things, but the teacher actually, interestingly, grew very fond of it.”
Once, when Odessa didn’t bring the CO2 device to school, the teacher said: “Oh, where is it? Please bring it.” Stephan believes that monitoring CO2 offers some reassurance that things are okay. It provides feedback on whether to keep the windows and doors open and how long they can be closed. It can encourage certain behaviors that one might regard as positive changes.
Once you notice the patterns and what to do to effect the necessary changes, Stephan realized that it wasn’t necessary to bring the device to the classroom every day. Stephan asked friends about having their children bring a device to their classroom. “One of our friends, when their daughter brought it to school, the school said: ‘Ooh, what’s this? No, you can’t have this, put it back in your locker.’” Stephan believes they were afraid of the information that it might reveal. The classrooms in the school did not have windows,
Stephan said he struggles to understand why institutions like schools are “scared of too much information. Personally, I am, like, give me more. I can do the filtering.” He thinks that at an institution, everything needs to be done officially. “Quebec did that. They went around eventually with proper sensors and scientists doing it all and gathered the information, but it is so slow.”
“They should allow parents or citizens in general to do something other than just sit on the couch and wait it all out. They should allow us to gather information and be happy about it being collected and used, even if it is just a snapshot or dirty. Even with a lot of dirty information, a lot of noise, you can filter out a signal eventually,” he explained. There is room for hobby scientists, he added, amateurs, which is what makers can be.
The friend’s school, which refused to allow the device, eventually came around. Stephan said: “The city, or the province came around and did proper testing. And, even though it was a room without windows, the quality was actually much better than expected, because they had a central air exchange system.”
Sharing His Work
Stephan shared the build instructions and code on Github for his CO2 project. He is not building a kit because this project reflects what he could do, himself, and with his family. It was a means to understanding what is happening during the pandemic, and doing something about it.
In Part 3, we will look at Guido Burger’s work, but here we see the basic elements of the CO2 device and its application:
- Hardware – a microcontroller connecting the following components
- A CO2 sensor
- A display to show the readings
- A data logger or alternatively, a wireless connection to collect and share data.
- Read the sensor and write it to the display
- Logic associated with various levels of CO2
- Graphing the data
Having a display — the larger the better — helps to make the readings available to anyone in the room. That’s the focus of the project by Carter Nelson, who developed and documented a CO2 project for Adafruit that we cover in Part 2: Make A Public Display.
Credits: Photos and Charts provided by Stephan Schulz