Build a Portable, Low Cost, Open Source Air Particle Counter

Posted by Goli Mohammadi on Nov 29, 2016 9:22:00 AM

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Here at OMC, we love seeing our community’s brilliance at work, particularly when it comes to fabricating solutions to everyday problems. We recently heard from Rundong (Kevin) Tian, a grad student at UC Berkeley who is involved with the powerful work produced at the Hybrid Ecologies Lab. Tian’s work has been previously mentioned in our case study on UC Berkeley’s CITRIS (Center for Information Technology Research in the Interest of Society) and its Invention Lab, where Tian first began working with the Othermill.

Tian's latest project—in collaboration with Sarah Sterman, Chris Myers, and Eric Paulos—is a three-part series called MyPart, which includes a Portable Open Source Air Particle Counter (pictured above), a Test Chamber for Air Particle Sensors, and a Monodisperse Particle Generator (pictured below). 

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We chatted with Tian to learn more. 

1. What inspired you and your team to design and build the Air Particle Counter, Test Chamber, and Monodisperse Particle Generator? In what order did you make them?

Particulate matter is one of the most harmful airborne pollutants with respect to human health. Airborne particles with a diameter of less than 10 microns (PM10) pose an especially large risk to human health—they can travel deeply into the respiratory system, causing a variety of cardiovascular and respiratory diseases.

Current sensors on the market that measure particulate matter are either bulky, inaccurate, or expensive. We wanted to address these metrics simultaneously to create a sensor that was small, portable, low cost, and accurate. We tested our build against the HHPC-6, a roughly $4,000 optical particle counter. Our bill of materials, at volumes required for one device, is about $75.

By open sourcing the entire design, we hope that individuals and communities can adapt these sensors for their particular applications, actively engage in air particle monitoring, and improve the sensor over time through collaboration.

For the latest iteration of the mechanical/electrical design, we designed and fabricated the sensor hardware and test chamber [pictured below] roughly in parallel. Previous prototypes were tested mostly in outdoor ambient environments, but we realized that building a test chamber sufficient for our needs could be done relatively easily and would give a lot more data throughput.

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2. What role did each member of your team have?

I designed the mechanical/electrical/firmware for the sensor itself. Sarah created the software to run the fully automated tests inside of the test chamber. Sarah and I worked together to build the various elements of the test chamber hardware, assemble sensor prototypes, and create the documentation. Chris Myers and Eric Paulos advised the project.

3. What was your general R&D process?

The electromechanical design was heavily iterated upon to reduce the overall size of the sensor. Various configurations of the laser/fan/photodiode/air channel were designed and tested to see if they would be insensitive to ambient light and count particles accurately.

4. What, specifically, did you use the Othermill for?

The Othermill was used extensively to mill ABS sheets to create the inner air-flow channels, which need to hold small features and tight tolerances, as well as have a nice surface finish.

We built an initial prototype of a low-cost diffusion dryer for drying calibration particles that come out of an atomizer. Various HDPE components for the dryer were milled on the Othermill.

Access to the Othermill was critical for rapidly iterating on the prototypes for this project. The alternative was to submit files to the job queue for a Haas VF-O VMC in our machine shop. The outer case is customizable for different use cases and is 3D-printed.

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5. What were some of the biggest takeaways you learned?

Documenting a project thoroughly is extremely time-consuming. Though it takes a lot more effort, it’s definitely possible for a graduate school research project to escape from the lab!

6. What are you going to do with the project next? Also, what other project ideas did you get while working on this one?

I'll probably need to work on other projects more related to my dissertation (novel tools/machines/software for digital fabrication)!  While I won’t be creating new air sensor prototypes, I definitely want to be active in the community and help people who are trying to build their own sensors or test chambers.

There's a lot that can still be improved, but we hope that this project can act as one starting point for people and communities to actively engage with air quality.

As for other project ideas, as we were wrapping up this project, I thought a little more about potential improvements that could be made to this sensor—in particular, a complete redesign of the electrical/mechanical system to use a small diaphragm pump instead of a fan. This could greatly simplify the air flow channel (ambient light leakage would be less of a concern since you could pull air through a much smaller orifice), get higher packing density of components (even smaller sensor!), and maybe even increase the accuracy of particle sizing. These components (injection molded plastic, diaphragm pump, op amps, microcontroller) are similar to those found in a blood pressure monitor, which is promising in terms of thinking about how low the cost could go.

7. Tell us a bit about the Hybrid Ecologies Lab.

The Hybrid Ecologies Lab explores scientific research, design, and art through the innovation, development, deployment, and evaluation of novel physical devices and interactive systems that advance our computing culture, encourage broad participation by non-experts within science and engineering, improve human health and well-being, and provoke critical debate and inquiry concerning our existing and emerging technological society.

More specifically, we are a research group at UC Berkeley in the department of Computer Science headed by Eric Paulos. We explore projects in the domains of software tools that support physical making, novel digital fabrication machines/processes, citizen science, and wearable technologies.

Some of the other projects in our lab can be found here.

 

Do you have a neat build you want to share with the OMC community? We'd love to hear about it! Drop us a line at support@othermachine.co