When I was teaching, I had a friend of mine ask me if I could review a grant proposal that his startup company (OtolithLabs) had written. In the proposal, they discussed a new device that would help with motion sickness by applying low frequency audio (or even sub audible frequencies) behind the subject’s ear. In the proposal, they had piecemealed a couple of Adafruit boards together to demonstrate feasibility for their new device.
What they needed was an electrical engineer that could create a small self-contained board to perform the intended function. My friend knew I was an electrical engineer (which was why he wanted my feedback on the proposal), but it never occurred to him that I could do their circuit design and consolidate it to one board. After hearing that, he set up some time for me to talk with their CEO about working on a design.
This was great for me because since I was teaching at the time, I was thinking about starting some consulting work to supplement my income. I figured I could do this project for free and use it to help me get started on other consulting projects. Little did I know that this would turn into 4 or 5 revisions and a near year-long project (off and on).
Eventually, I was able to get to a prototype design that allowed some pre-trial testing which was very successful. At that point, I suggested that they bring someone on full-time to help optimize the design and to take it to production.
While I can’t share specifics of the design, I can share the general functionality. Essentially, it was a low frequency waveform generator that drove a custom transducer. The transducer was designed by another engineer who was also working on the project. The transducer had a very high Q, but the resonant frequency had some variation that required my circuit to be tunable. In an early revision, this was tunable by the user, but in the last revision I added functionality to auto-tune to the resonant frequency by sampling the current and voltage to the transducer. I did all this with an ATMega 32U4, so I was really pushing this microcontroller to it’s limits! In hindsight, I should have used a faster 32-bit microcontroller.
The manually tuned version of the board is shown below (6 boards paneled together). I used DipTrace for the PCB design and OshPark to manufacture the boards. For those interested, I used the Arduino environment to create the firmware. On the left side of the board, you can see 6 LEDs that were used to indicate the active frequency (in binary). I ended up making around 20 of these boards for the pre-trial tests using my toaster oven turned solder reflow oven.
The final revision of the board is shown below. It includes circuitry to sample the delivered signal to the transducer so that the frequency could be auto-tuned. It also included circuitry to handle Li-Po battery charging. One of the requirements was that the board needed to be as small as possible (around 1″ x 1″), so I had to fit a lot of functionality in a small space. The final prototype below was around 1.2″ x 1.2″. To keep things small, I used 0402 passives. I usually use 0603 passives as a standard, and I went back to 0603 after this project! (0402 is a bit too small for me to comfortably deal with for most projects!)
By working on this project, I learned a lot about what consulting entails. If I ever did serious consulting I would definitely do some things differently. While I did hand over all of my design files, I have no idea if the company is using any part of this design in the production version of their product. (I really doubt it.) Hopefully, I was helpful in bringing them along in the prototype process, though.
If you’d like to know more about this product and how it can help with motion sickness (and VR sickness), visit their webpage: otolithlabs.com.