Plan CO2: Making A Public Display

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Plan CO2: Making A Public Display

This is the second 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.

When I saw the big emoji (old school – smiley) on Carter Nelson’s RGB Matrix Portal Room CO2 Monitor project on Adafruit, I knew he was on to something.  I wished that I would begin seeing more such displays in places like restaurants and shops, not to mention school classrooms, offices and makerspaces in the coming months.

Making CO2 visible is what the CO2 sensor does for us but just showing the data itself (PPM) doesn’t tell us what it means.  Is 500 a good number?  Is 1100 cause for concern?  In Carter’s Adafruit project, the CO2 monitoring device presents a concise public-health message. Framed up, the display measures 6.5″ x 11.5″. At this size, anyone in the room can read it and be alerted to changing conditions in the room. It is a warning system that can prompt people to improve room ventilation.

Creating a visible display of the sensor readings is a really good idea; it is better than sending data to a smartphone or collecting it on a webserver, although that can be useful as well.  The changing message can make people curious, ask questions, and eventually think about what actions to take to change the CO2 levels in the room. In a separate article, we will see many creative variations on displaying CO2 readings, starting with Guido Burger’s CO2 Traffic Light. These different ways to communicate that the ventilation in a room is good, not so good or bad.  

Carter’s project shows four levels, each level represented by a smiley, a color and a word, which appear above the number.

Screen shot of smileys associated with CO2 levels

The intent, said Carter, was to create “an indicator so that maybe you want to open a window or maybe you want to open the door. And when you do that, the display will hopefully change.”  It is simple and straightforward. 

“There’s nothing magic about 1000 being the cutoff for ‘good’,” he said, and one could associate symbols with different levels.. “I based mine on subjective research,”  he said.  He found information on CO2 levels in OSHA’s Indoor Air Quality guidelines in Appendix A, which says::

CO2 levels can be used as a rough indicator of the effectiveness of ventilation (26), and excessive population density in a structure. 

OSHA Indoor Air Quality Guidelines

Carter labeled his highest level, “Dang”, sort-of short for “Dangerous” but readings over 5000 are not necessarily an immediate danger but action should be taken to prevent prolonged exposure.  

However, for this application of indoor CO2 monitors, we aren’t necessarily worried about really high levels of CO2.  CO2 monitoring can provide feedback on proper indoor air ventilation, which can reduce the risk of airborne transmission of Covid-19. We looking for rising levels of CO2, which might mean that fresh, clean air is not coming into the room or that more people are now occupying the room, which might not be safe.   Real-time feedback means that anyone in the room can initiate appropriate action.

RGB Matrix Portal Room CO2 Monitor Project

Carter Nelson

Carter Nelson, who has a background in aerospace engineering and lives in Seattle, writes DIY projects for the Adafruit Learning System.  One of his projects last year is for testing masks.  Limor Fried, founder of AdaFruit Industries, saw the story on social media of Stephan Schulz and his daughter, Odessa and how they built a CO2 monitor using components from Adafruit.  She asked internally if anyone wanted to create and document a CO2 device project and Carter stepped up.  She left it pretty open what to do, he said. He came up with using the Matrix Portal as a display. 

“Every now and then when an idea comes up,” said Carter, talking about the back-and-forth at Adafruit. “We just discuss it and go: I got it. Let’s do it. That’s a great idea.”  For some  projects he’s done, he’s had the idea and he would ping Limor about it or she’ll have a seed of an idea and they’ll ping him. “It just grows from there,” he said.   He posted the RGB Matrix Portal Room CO2 Monitor Project on February 2, 2021. 

He noted that most of the components needed for the project were shipped in Adabox 016. The parts for this project cost about $100, he estimated.  “Basically you need the sensor, the Matrix Portal board and an RGB matrix,”  he said.  The parts are listed in the project, of course, but the key components are:

The application is written in CircuitPython (Github link). 

A Simple Build

I asked Carter if he thought that students could build this CO2 monitoring project?  “Absolutely,” he said.  “It’s really easy, especially with that hardware. There is zero soldering involved and all the parts just plugged together.”  He added that CircuitPython, “is super easy to get spun up on.”  He thinks that the device can be up and running in five minutes.

Carter also added that his project guide shows just one way to do it. “If you want it to use some other display, you could pair it with a different CircuitPython-supported board.”  He originally thought of using the Adafruit Clue or the PI Portal because those are boards that have a display.  (Stephan Schulz, featured in the the first article in this series, connected the Feather M4 Express and the same CO2 sensor and used a small LED display that fit on the board.) The goal of “making the display viewable in an entire room was why I chose the RGB Matrix,” said Carter.

I asked him if he had any tips for a person building this project.  He said to “follow the guide and be very patient. Maybe verify that the CircuitPython installation works first before actually trying to run this specific code. If you’re new to CircuitPython, there are great guides for learning, which might be a good place to start before doing this project.”

Carter is happy with the way his project came together.  He said of the CO2 display: “It’s nice and big and bold and blocky and very simple.”  Phil Torrone and Limor Fried of Adafruit wrote that “We’ve made and deployed these Python powered RGB Matrix Portal Room CO2 Monitors on each floor at Adafruit. It allows our team to see the air quality at the workplace real-time, it’s one of the many protocols and devices we’ve added to keep safe and aware.”

Wouldn’t it be nice to begin encountering such devices in restaurants and bars, retail stores and offices? 

If you deployed a CO2 monitoring device to monitor ventilation in a classroom, office or retail business, please let me know.  (dale at

Credits: Project photos from Adafruit; Carter Nelson’s photo was provided by him.

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DALE DOUGHERTY is the leading advocate of the Maker Movement. He founded Make: Magazine 2005, which first used the term “makers” to describe people who enjoyed “hands-on” work and play. He started Maker Faire in the San Francisco Bay Area in 2006, and this event has spread to nearly 200 locations in 40 countries, with over 1.5M attendees annually. He is President of Make:Community, which produces Make: and Maker Faire.

In 2011 Dougherty was honored at the White House as a “Champion of Change” through an initiative that honors Americans who are “doing extraordinary things in their communities to out-innovate, out-educate and out-build the rest of the world.” At the 2014 White House Maker Faire he was introduced by President Obama as an American innovator making significant contributions to the fields of education and business. He believes that the Maker Movement has the potential to transform the educational experience of students and introduce them to the practice of innovation through play and tinkering.

Dougherty is the author of “Free to Make: How the Maker Movement Is Changing our Jobs, Schools and Minds” with Adriane Conrad. He is co-author of "Maker City: A Practical Guide for Reinventing American Cities" with Peter Hirshberg and Marcia Kadanoff.

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