In the past, building construction methods generally didn’t worry much about air quality. There were enough gaps around windows, doors, siding, and flooring that a house could naturally “breathe” and do a decent enough job of making sure the occupants didn’t suffocate. Modern buildings, on the other hand, are extremely concerned with efficiency and go to great lengths to ensure that no air leaks in or out. This can be a problem for occupants though and generally requires some sort of mechanical ventilation, but to be on the safe side and keep an eye on it a CO2 sensor like this unique Pac-Man-inspired monitor can be helpful.
Although there are some ways to approximate indoor air quality with inexpensive sensors, [Tobias] decided on a dedicated CO2 sensor for accuracy and effectiveness, despite its relatively large cost of around $30. An ESP32 handles the data from the sensor and then outputs the results to an array of LEDs hidden inside a ghost modeled after the ones from the classic arcade game Pac-Man. There are 17 WS2812B LEDs in total installed on a custom PCB, with everything held together in the custom 3D printed ghost-shaped case. The LEDs change from green to red as the air quality gets worse, although a few preserve the ghost’s white eyes even as the colors change.
For anyone looking to recreate this project and keep an eye on their own air quality, [Tobias] has made everything from the code, the PCB, and the 3D printer files open source, and has used accessible hardware in the build as well. Although the CO2 sensors can indeed be pricey, there are a few less expensive ways of keeping an eye on indoor air quality. Some of these methods attempt to approximate CO2 levels indirectly, but current consensus is that there’s no real substitute for taking this measurement directly if that’s the metric targeted for your own air quality.
interesting texture / look of the 3D print …
Thank you. There is a pixel pattern on the inside which is more or less noticeable depending on the viewing angle.
This is a good start. I recommend moving to the next phase of the project, where you call for the HVAC fan to run to filter particulates, or open a fresh air vent to bring in fresh air from outdoors when the indoor VOCs are high. Nice work.
Even better, use it to turn on an already installed energy recovery ventilation (ERV) fan. We have an ERV and it is controlled by a stupid little panel that you set the percentage run time on. (ERVs are required by code for new construction here.) And what % should we set the thing to? Nobody, including the HVAC system installer, has given me a good answer for that. He says our house does not really need it.
An ESP32-C6 is used in the project. Shouldn’t be a problem to implement this using the available 802.15.4 (e.g. ZigBee) or Wifi capabilities ;)
I intended the overpowered controller to add the device to the home automation system in the future. Thank you for the suggestion.
Does the “ghost” flash ever increasingly as CO2 limits are approached?
Does it play a recording of the sound Pac-Man makes when he’s dying if CO2 levels are exceeded?
Not yet, but feel free to implement it the way you like. The Arduino code is included with the project files.
Unfortunately the device does not have a speaker. I really like the idea of playing “game over” samples on high CO2 levels. Might consider this for a new revision :)
Interestingly, engineered closed spaces like submarines and the space station let the CO2 concentration float around 0.5%, twelve times ‘normal’ atmospheric CO2, and a tenth of your exhaled CO2 concentration.
You exhale around 20 litres per minute, so diluting that 10:1 with fresh air will keep CO2 to that target 0.5%. If each person occupies 100 cubic metres of space (2 people in a small house or 6 people in a space station), that’s just one air exchange every 8 hours.
The point: other human gasses probably become objectionable before the CO2 does. CO2 is just a proxy to measure air exchange, but measuring other contaminants is perfectly valid. Expensive CO2-specific detector isn’t necessarily needed.
One slight exception to your “CO2 is a just proxy” statement – houses with gas cooking appliances have a big source of CO2 that you hopefully wouldn’t find on a submarine, and in a reasonably well-sealed house, it can actually build up enough to have an impact on health directly.
(The expensive CO2-specific detector may still be overkill in that situation, though, since it works both ways – a general VOC or particulate sensor could also function a proxy for CO2)
True. But to be fair, if you’re using gas appliances indoors without ventilation you’re a Darwin award candidate. (I have 5 gas appliances in my house and, yes, they all vent outdoors)
“yes, they all vent outdoors”
Including Uranus?
B^)
I served on a diesel sub and I can tell you you don’t need a sensor when the CO2 concentration gets high. You can sense it. You can breathe as hard as you want and still long for more air. I’ve seen it where a match won’t stay lit.
matches need oxygen to burn. If a match won’t stay lit you were in a low oxygen environment. While both hypoxemia and hypercarbia will make you feel like you’re dying they are pretty different. Not saying it couldn’t have been both or whatever. And also as a professional in the field I chuckle when people worry about high CO2 being somehow toxic or bad in a office. I guess they don’t realize that you have about 40mmHg of CO2 in your blood and as long as the air concentration is less than that (and in article and comments they are talking tiny levels compared to that) a normal human will compensate just fine.