It's been two years since I developed the Arducorder Mini, and I have found myself brainstorming about what a next model would look like over the past few months. It feels like it's time to work on the next iteration of my open source, handheld, pocket-sized scientific instruments -- Iteration 8.

Arducorder Mini: What went right

The Arducorder Mini was a substantial undertaking, and turned out exceptionally well -- it's personally my favorite open sensing project, and I very much enjoyed the development process, and getting to see the final product. I'd like to briefly describe what went well with the project, and what could use improvement:

• Diversity: The Arducorder contains nearly a dozen very different sensors.
• Capability: Spectroscopy, radiation sensing, and thermal imaging have all been sensors on my wishlist for handheld sensing devices for quite some time. Here, these sensing modalities finally began to be incorporated. Other sensors, like the barometric pressure sensor, have so high a resolution that you can often measure someone's height simply using the difference in air pressure between their head and feet!
• Connectivity: Ability to share many of the sensor readings wirelessly through Plotly.
• Interface: A simple, visually attractive interface, that is very usable for core tasks.
• Reuse: In the spirit of open source, many of the aspects of the Arducorder were individually reused for other projects. Most notably, the Arducorder serves as a reference design for the Hamamatsu microspectrometer, and the folks at GroupGets helped use this to bootstrap and enable a community of makers and engineers to order and use small quantities of these beautiful microspectrometers.

Arducorder Mini: What could have used improvement

Many aspects of the project worked very well. As with all experiments, there was room for improvement:

• Usefulness: The Arducorder Mini is has the most diverse array of sensors of any portable electronic device that I'm aware of. One of the most common questions I get asked is, "What can I use it for?". Individually, there are many applications for each of the sensors apart from science education -- for example, thermal imaging can be used to find heat leaks in your home, or for various tasks in industrial settings. Radiation sensing is something that likely isn't a part of everyday life for most folks, but the Arducorder Mini's radiation energy histogram showed an unusually high concentration of very high energy particles while sitting on my desk one afternoon when there happened to be a solar flare -- likely my first handheld solar flare measurement! Does this mean we can create crowd-sourced cosmic ray observatories with some large number of handheld instruments such as these? Similarly, the visible light spectrometer is an extremely powerful instrument, but needs much more work on specific applications, and industrial design supporting specific kinds of common measurements -- for example, allowing absorptive measurements through small sample vials. The list goes on. All together, the device is quite capable, but identifying and then developing specific use scenarios will help increase it's usefulness.
• Industrial Design: It is extremely challenging to meet the mechanical and industrial design requirements for a dozen different sensors. Some of the readings (for example, from the atmospheric temperature sensor) are not accurate, because the unit heats up quite a bit from the battery and processor. Gaskets are missing on atmospheric sensors. As above, sample container adapters and/or other mechanisms for absorptive measurement need to be incorporated to increase the utility of the sensors in common use cases.
• Ruggedness: The design is pretty solid, but not solid enough that I feel comfortable carrying it around everyday in my pocket without fear that I'll break it after a week or two of constant use. When I ship it to folks to use in demonstrations, it sometimes comes back with some of the sensor boards unconnected (from rattling during shipping). Ideally the next iteration of a design would be something that could be carried around in one's pocket everyday without having to worry.
• Build time: The Arducorders take forever to build. It takes me two weeks of evenings and weekends to build one, and I designed the thing.
• Replicability: While every effort was made to make the Arducorder replicable and as easy-to-build as possible, it is a project with nearly 200 very small surface mount components spread across 7 boards, and I have to accept that this is simply beyond the capability of all but the most motivated and experienced makers/citizen scientists. The next iteration has to make serious improvements in lowering the barrier to construction.
• Maintenance: I am only one person, and this is a project with an extremely large hardware and code base. In spite of rewriting the Plotly Arduino library, plotly changed the streaming interface a few months later, and I simply didn't have time to update the library, so this feature became deprecated. I broke the firmware for the thermal camera part way through the build, only discovering it was a software issue after making several copies of the board when it mysteriously quit working (though I didn't have time to find and fix this bug). I had hoped to bootstrap a community of makers that would continue to develop the hardware and code, but due to the barriers to making one's own unit, this never happened. In a very real way the project can't be successful unless I not only design a capable device, but make it easy enough to replicate that it bootstraps a community that's able to further develop and maintain that device. This is something that I'm still learning to do, though I think I get better at it each time.
• Time: The Arducorder took a very large number of person hours to develop. As a postdoc, most of my evenings and weekends for six months were spent designing and building the Arducorder. Now that I'm a professor in my first year on the tenure track, nearly every evening and weekend is spent working on papers, doing my teaching, and applying for grants to support my research at a time when public scientific funding is extremely low. All this means that I have to make design choices that don't take tremendous amounts of time to develop, and have a high chance of working out. Hopefully this will implicitly help reduce the build time, and increase replicability.

A first roadmap for the next iteration

I've assembled a first-pass at a roadmap for building the next iteration, that hopefully embodies many of the design principles outlined above. The significant differences in design principles from the Arducorder are:

• Breakout Boards: To make the design as easily replicable as possible, try to build the device using existing breakout boards from major suppliers (e.g. Sparkfun, Adafruit, etc) whenever possible. If a part or sensor is too new, try and convince a supplier to carry a breakout board for this. This will increase the size, but also greatly decrease the barrier for construction.
• Interface with a smartphone: Smartphones have beautifully usable interfaces, and are very good at displaying information, interacting with the user, and communicating with the world -- exactly the bits that are often most time consuming. Here, try to make a backpack that will fit on the back of a smartphone, and interface between the two ideally with a wireless method (e.g. wifi). Hopefully this should simplify making a robust enclosure, and the whole thing can just be attached to the back of a smartphone and carried with you wherever you go.
• Target the mechanical design around use-case scenarios: Figure out common use-case scenarios for each sensor, and design the mechanical considerations of the device around these. Does the spectrometer need an integrated sample container holder to be able to be broadly useful? Or a method of easily performing absorbance measurements? Do the atmospheric sensors need to be mounted in a tube that periodically samples air using a microfan to be most useful and accurate?

It looks like an exciting (and hopefully tractable!) project, and it'll be great to go through the design process to see how things take form as time progresses.

Thanks for reading!