Inspired by an article on the use of ventilation and air filtration to reduce the spread of coronavirus indoors, Guillermo Amat has created a DIY method for building a CO2 detector, available on GitHub. The vast majority of coronavirus transmission takes place indoors — and since 40% of cases are asymptomatic, it is impossible to be sure that no one in a given room is infected. While masks do a decent job, proper ventilation is key to keeping indoor spaces safe. How do you know if the room you’re in has enough air exchange to be safe? Since we release CO2 with every, exhale, measuring CO2 levels can be a handy estimate of whether the room the is stale and potentially hazardous.
This DIY model is simply a sensor board with LED indicators to give you an idea of how stale the air in a room is at a glance. Built with a Wemos D1 mini and programmed using Arduino IDE, a green, yellow, or red light indicates the current state of the air. The device sends data to an IoT gateway via an MQTT queue. In the case of the prototypes the designer is running, the data is sent to a SolidRun CuBox-I mini PC running Home Assistant. At the same time that the LED indicators light up depending on the PPM of CO2, information gathered from temperature, humidity, and air quality sensors are viewable via Home Assistant, complete with current status and history.
The main hardware components consist of the Wemos D1 mini, a DHT22 sensor, an SGP30 sensor, and the green, yellow, and red LEDs, as well as the wires and tools needed to connect the components. The software portion uses Arduino IDE and its standard libraries, as well as the additional libraries WiFiManager, Arduino Json, PubSubClient, DHT and Adafruit SGP30. It also requires a computer running MQTT, though running Home Assistant is optional. A step-by-step configuration walkthrough is available on the GitHub page, along with the full BoM and the required code.
Having an idea of the air quality in your home or other places you frequent is a great step toward staying safe, especially as we all spend more time indoors this winter. The green indicator lights up for less than 600 PPM of CO2, yellow for between 600 and 800 PPM, and red when the CO2 is greater than 800 PPM. For comparison, outdoor CO2 levels are just above 400, and a well-ventilated room will generally have above 800. However, research has shown that improved air circulation reducing levels to under 600 can greatly reduce risk. When tested at Taipei University, this improvement stopped an outbreak completely. This tiny device can let you know when you’re relatively safe and when it’s time to take steps to improve air circulation.