CO2 Sensor for Schools
Introduction: CO2 Sensor for Schools
Background
The scientific understanding of COVID-19 transmission has turned away from the early, highly-publicized measures of fomites (touchable objects that can have the virus on them) and is now focused on aerosols (small, airborne particles that may not drop onto surfaces). Detailed reading here.
Simply put, perhaps your biggest concern regarding COVID transmission should be clean air.
If you are breathing air that has already been exhaled, you could potentially be breathing in aerosols containing the virus. Carbon dioxide (CO2) is a great indicator of the amount of previously respired air in a room - the air we exhale is 4-5% CO2 which is 100 times the amount of CO2 in air we inhale. So CO2 will build up in a room with poor ventilation, just as COVID-containing aerosols will.
With schools, and other places of business, returning to in-person activities, it is challenging to know the air quality in a room. CO2 sensors are a pretty good way to indicate how dense the amount of previously-respired air in a space is, and therefore how much potential COVID could be in the air.
There are good CO2 sensors on the market (We like the Aranet4), as well as quite a few bad ones. General tip: make sure to spend the money on an NDIR-based sensor. We can also make our own for about half of the price! This project comes in around $70-$80 in supplies vs. $150 or more for reliable, 'store-bought' NDIR CO2 sensors.
Created by the Innovation Lab at La Jolla Country Day School, La Jolla, CA, USA.
Supplies
Note: We link to Adafruit when possible because we believe in their company philosophy. You can order these same parts at other places.
Arduino Nano Every - With headers attached if you want to have minimal soldering required.
Sensirion SDC30 CO2 sensor board ($50-60) - This is a highly accurate and reliable board utilizing NDIR technology. 152
We think it is the best in class and has useful documentation from SparkFun. You will have to purchase and solder your own headers on to the sensor. Otherpurchasingsites.
Headers - Any headers (plug to plug) will work! Need 7 to solder to your SDC30 Sensor.
RGB LED - We use an RGB LED to indicate the CO2 levels via color. Possible to use three, individual colored LED's instead!
Sunfounder LCD1602 - Many LCD Screens *could* work, but the code and pinouts are specifically designed to be used with this style. Note: The LCD takes a lot of power, so not recommended for battery power.
Half-size Breadboard
Plug-to-Plug (M/M) 75mm Jumper wires
Depending on what USB ports your computer has pick one:
USB Cable - USB A - Micro - (*Most* computers feature at least 1 USB-A port)
USB Cable - USB-C - Micro - (Newer computers have more USB-C. Since 2019, MacBook's have been exclusively USB-C ports.)
Equipment Needed
Soldering Iron. The CO2 sensor does not come with headers attached. Learn to solder.
Optional: Laser Cutter or 3D printer for a housing.
Step 1: Assemble
While assembling the circuit, please be mindful of a few things:
* The wiring for the RGB LED can be a little bit tricky to place the legs into the correct slots as shown in the photo. There's enough space to bend the legs and get them in the right slots without having any of the 4 legs touch, but it's always a good idea to have a couple extra LEDs in case the legs end up getting too bent :)
* Your Arduino and SCD30 may not have the slots labeled exactly as they are in this diagram, so make sure that you're plugging from the TX/SCL port on the arduino (The image shows a4 but the pin does both!), to the TX/SCL pin on the sensor, and similarly for the RX/SDA pins.
* On the topic of labels being slightly different, the farthest left pin (VDD or VIN) is where you want your power for the sensor to route to.
* Specifically this is set up for a 16 x 2 LCD screen that uses a 4 pin I2C backpack (as pictured and as linked in supply!)
* Make sure you power the LCD screen with 5V, and the Sensor with 3.3v! If you try to power the screen with only 3.3v you're going to have some problems :)
* Don't forget about the brightness adjustment on the back of the LCD Screen! 611