The Air We Share

building a monitor

New regulatory monitors can cost up to 17 grand. This means that DC only has a handful of them, spread thin across a city where air quality varies block by block. So I built a low-cost monitor from scratch, inspired by a design from a UC Berkeley paper one of my mentors, Dr. Hsieh, sent me, and I adapted it to monitor air in DC.

monitor diagram from the UC Berkeley paper.

What’s inside:

At the heart of the monitor is a simple optical principle: black carbon particles absorb light. Pull air through a filter, shine light through it, and measure how much gets through. Less light means more soot has collected on the filters. 

The hardware breakdown: 

FDS100 photodiodes: light sensors that measure attenuation through the filter

DS321 real-time clock (RTC): timestamps every reading

880nm LEDs: 880nm is the wavelength at which black carbon absorbs light.

DHT11: tracks temperature and humidity, since both affect sensor readings and need to be corrected for.

D6F flow sensor: measures the airflow being pulled through the filter, which is essential for calculating the black carbon concentration.

SD card logging: stores data.

Arduino Uno: a processor to manage the data and voltage.

Schwartzer/135 FZ: air pump.

3D Printing:

The first step was figuring out how to adapt the design such that it could be 3D printed.

screenshots from my design journal.
My 3D printing prototyping process.

Circuits:

Building the circuit was one of the hardest parts of the project! I had to figure out how to fit all the components together with the correct resistance and voltage on each component. Special thank you to Declan Leighton for helping me with building the circuit.

Coding:

I had to work through a couple of bugs in my code, including difficulties with the temperature sensor, and issues with the baud.

The final monitor:

While the monitor is not yet calibrated, I built it for less than $100 as a proof of concept for lower-cost monitors.