Prototyping a Tennis-Tracking Device in Shenzen: A Lesson

For makers, engineers, and DIY enthusiasts, Shenzhen, China is a bit of a dream world. Once you get past the shoddy internet and questionable origin of the components you buy in the markets, you realize just how quickly and easily you can get almost anything done. For about $100 you can get a couple dozen 4-layer PCBs and a stainless steel stencil. For another $50 you can get it in 2 days. That’s seriously cheap, and the game changes when you have such ready access to fast, cheap manufacturing. The electronics market puts Wal-Mart to shame, and you can’t walk 20 feet without bumping into someone carrying a reel of components or pushing a cart full of capacitors. I was there with Lavie Sak, my co-founder for Shot Stats, makers of Challenger, a tennis swing tracking device. We were excited and overwhelmed by this new place and it seemed like anything was possible.

Prototyping a Tennis Tracking Device in Shenzen A Lesson

One of the phrases I heard repeatedly from our mentors while attending HAXLR8R in Shenzen was “Oh … yeah, that’s gonna be a Challenge.” That and the Mandarin phrase “One of these!” whenever the gang went out to a restaurant, instantly turning any place into the international point-at-the-menu championship. As much as I feared restaurants without picture menus, I was much more afraid of the unknowns involved with prototyping a new and ambitious product. Our mentors were wonderful but quite often they re-iterated just how tough this whole process would be. They were right of course; we’d picked a very challenging product to build.

We had brought our first prototype, a clunky little thing with a 3D-printed SLA housing, which only showed two metrics. That one contained an Atmel xMega MCU (which I grew to dislike rather quickly), an Invensense MPU-9150 IMU, and not much else. I realized pretty soon that we were going to need a lot more power since much of our data crunching is done onboard. I knew what we wanted: audible feedback, Bluetooth, an OLED display, multiple motion sensors, and a powerful processor. Making lists is easy, but turning that list into a product is not.

I spent a couple nights perusing datasheets with a mouse in one hand and an old fashioned in the other, as one does on the weekend. I soon settled on the ARM architecture. At this point, except for the most basic or low-cost projects, it just didn’t make sense to use anything else. They’re fast, cheap, plentiful, and incredibly well supported. I was wary of using the Arduino platform as a base for our first fully-functional prototype. The Arduino is great and I’ve used it plenty, but I still see it as firmly situated in the “hobbyist” category and not really a good option when your end-game is manufacturing a finished consumer product. There are shields for everything but they are a bit too clunky to attach to a tennis racket for testing, which meant our best option was a custom PCB.


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