I spent some time searching for small microcontrollers. There seemed to be many promising results at first, but I’ll go into more detail below:
- Gemma is 1” diameter, so nice and small. In addition, it comes with a tutorial for how to control a bunch of Neopixels in different colors with just 1 pin, so this is a good sign that we don’t need to individually pin each LED (which would save a lot of wiring and pins). Unfortunately, Gemma was eliminated because a) there wouldn’t be enough pins left to hook up 3 microphones and Bluetooth, and b) it doesn’t support USB charging of batteries, which would be very convenient instead of asking the user to take out the battery and recharge: Adafruit GEMMA M0 – Miniature wearable electronic platform : ID 3501 : $9.95 : Adafruit Industries, Unique & fun DIY electronics and kits
- Circuit Playground Express has lights directly on the board, so that would also conveniently save the need to buy separate lights. It’s also a bit bigger than Gemma, at 2” diameter, but it also comes with more pins. This was eliminated because a) our initial idea was for lights to be around the wrist for better viewing, and b) no Bluetooth built in: we estimate that controlling Bluetooth would be more difficult that controlling lights, so we’d rather have the Bluetooth interface be easier. Circuit Playground Express : ID 3333 : $24.95 : Adafruit Industries, Unique & fun DIY electronics and kits
- FLORA is 1.75” diameter, so in between the above 2, but it also has many pins, which is nice. Since it’s marketed as a wearable electronic, that’s a good sign for being safe to use close to the body. Unfortunately, this one also doesn’t have a built-in charger or Bluetooth. FLORA – Wearable electronic platform: Arduino-compatible [v3] : ID 659 : $14.95 : Adafruit Industries, Unique & fun DIY electronics and kits
- The only rectangular one of the list at 1” length, Trinket M0 also decently small with many pins. Unfortunately, like the FLORA, it was eliminated for not having a built-in charger or Bluetooth. Adafruit Trinket M0 – for use with CircuitPython & Arduino IDE : ID 3500 : $8.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Conclusion: although these candidates ended up being eliminated, these possibilities were still important in helping us narrow down our use cases and think more deeply about implementation. The first big takeaway is that we’ve proved that we only need 1 LED pin to individually control a whole array of lights (with the help of the libraries listed in the Gemma pendant link tutorial), which also helped us discover that NEOPixels were a nicer alternative to LEDs. Second, we had a good discussion about ranking what we value most in our parts, such as whether Bluetooth or LEDs were more important, and also how to charge the battery. Initially, we thought it would be fine to take the battery out to charge, but since the battery wires are likely going to be soldered to the switch, that’s probably not possible. This isn’t something we would’ve thought of if it weren’t for comparing all the different features of the microcontrollers we had available and ranking what we valued in our use cases.
I think the project schedule is on-time with the new Gantt chart changes, now that we have our main parts decided upon. However, we shouldn’t slow down the pace given that it did take changing the Gantt chart.
Next week, I plan to start finding 3D models of all the components we will be using, and trying out different arrangements to see how they’ll fit together, so we have an estimate and can be prepared before parts arrive. We can also analyze responses from our user survey to see if there are other design implementations we can narrow down, and go from there.