One of the many difficult things about the COVID-19 pandemic, as we hopefully move toward safer times with the vaccine, is that you are so often unable to know whether or not you have been exposed. One way to have a better idea of the safety of any space is to test the air quality; testing CO2 levels indicates how stale or “fresh” the air is, and therefore how likely it is that you might be breathing in hazardous particles. Pierre Carles has proposed a cheap and easy-to-use device to monitor and record the real-time concentration of CO2 in ambient air. Using CO2 as a proxy for respiratory aerosols, the data obtained can help determine whether you need increased ventilation in any closed space, which is an important safety measure when dealing with the coronavirus.
The BOM for the unit is laid out in full in the post, and Carles estimates that all materials can be purchased for $120. The main components include a Gravity NDIR CO2 sensor, an Adafruit Feather 328P or similar Arduino-compatible board, a Adalogger FeatherWing or any separate SPI SD card and I2C RTC boards, and an OLED FeatherWing or another I2C-addressable OLED screen. The rest of the electronics consist of a 5mm RGB LED, a CR1220 battery, a USB power bank, wires and tubing, and a box to serve as the enclosure.
The first step in building the monitor is to install headers on the microcontroller, as well as the OLED screen and Adalogger. Once the boards are stacked, the microcontroller can be connected to your computer to upload the code and test that they are working. The code for the project is available via the GitHub repository. Next, the circuit is constructed, connected to the LED and CO2 sensor. The simple circuit design followed for the project does not include a power source; instead, a micro-USB power supply or power bank can be plugged directly into the Feather board. This means no boost circuit is needed to accommodate the sensor requiring a 5V input current to the 3.3V Feather board.
The device and power bank can all be housed in one casing, using any box of appropriate size and making holes in it wherever is needed before securing the components inside. Everything is deliberately small, intended to be portable. For accurate readings, it is recommended that you place a CO2 sensor at a height between three and five feet, away from doors and windows. The indicator is also intended to be unobtrusive and not anxiety-inducing. It’s useful for gauging the air quality in a space and making adjustments accordingly, not to signal immediate danger. Ventilation actions can be as simple as opening a window or increasing circulation. It’s just another check to make it easier to ensure our safety and that of people who share space with us.