portable-co2-monitor
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Overview
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Recent research has shown possible correlations between high CO2 concentration in indoor environments and decreased cognitive function. As someone that is curious about optimizing my brain for productivity, I wanted to investigate this correlation.

This idea started when I attended an office hour for my algorithms class. This took place in a very small room, packed full of students. I immediately felt the thickness of the air in the room, and shortly after, lost focus and forgot my question. I left for a bit to reconcentrate, believing that I might be tired from a lack of sleep. However, when I went back into the room, I lost my focus once again. I heard about CO2 fatigue from a YouTube video and was curious about it.

I looked around on Amazon for a cheap monitor, but the majority of the devices I found were above $100 (there are a lot of new devices below $40 now). I was not willing to spend so much money on a curiosity, so I decided to look for a cheap alternative.

V0 Prototype Design
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I looked on AliExpress to see if I could find a cheap sensor to use. I quickly found the SenseAir S8 for around $20, and decided to buy one.

I used a spare Arduino Nano 33 IoT that I had on hand and attempted to connect it to the SenseAir S8. I found this article describing how someone else connected their Arduino to this sensor, so I followed their process to create my code. I had to slightly modify the code to work with the hardware serial connections instead of using the SoftwareSerial package, but otherwise had minor issues.

After verifying that the sensor works, I decided to begin designing ways to make the device more portable. This began with a CAD model.

My goal here was to try to visualize the parts so that I could think of ideas on how to integrate everything. I printed this at my local makerspace and proceeded with integration.

I roughly put the parts on a sheet of perfboard and measured out the width that I decided on for my CAD model. Everything seemed to fit, so I proceeded to cut the board.

I decided to flip the CO2 sensor because the foam diffuser needs access to air, and I planned to face this towards the side of the mount.

I connected up the pins of the Arduino and the CO2 sensor using solder and wires. Yes, I lack good soldering skills.

The wiring is as follows

Green Wire: Arduino TX Pin <-> SenseAir S8 RX Pin
Blue Wire: Arduino RX Pin <-> SenseAir S8 TX Pin
Red Wire: Arduino VUSB <-> SenseAir S8 G+ Pin
Black Wire: Arduino GND <-> SenseAir S8 G0 Pin

Back side of perfboard with soldered wires

The next step was to somehow mount the board into the case. However, although I was planning on powering the device over USB, I realized at this point that this was not feasible because of a lack of space. I then decided to cut a broken USB cable and solder it directly to the board.

Next was to shove the board into the case and mount it somehow. I decided to put a screw through the case and the board, and then attach it with a washer.