If you consume power over USB-C, 2 resistor are enough.
But for providing power over USB-C, you generally need a dedicated IC to handle VBUS switching. It wasn't worth it.
Also, once you ship a consumer product with a USB port on it, you'll realize a lot of people really don't understand how USB works, and USB-C doubly so. Square holes for square pegs goes a long way.
First, so far, there have been 0 failures in the field. My email address is on the website, the app, and the first page of the instruction sheet, so I'd probably know if there were.
But since it's fun, I'll address some of these :) I'm not flying by the seat of my pants here as much as you expect.
- The ESP32-S3 includes ±2 kV ESD, which is respectable. Adding more is a bit precautionary IMO, but I did add it in some places where the user is more likely to touch metal (like the USB ports). The sdcard's metal housing is not exposed.
- The AMS1117 is just more available than the alternatives. Again, no failures yet so seems like the right tradeoff was made here.
- Supercaps don't last long enough for my liking. A CR2032 can go for 10+ years. A supercap, only weeks. I want correct dates even if the device is left unpowered for months.
- The 0603 47ohm resistor is a good callout. Worth beefing that up. But at 3.3v and 232 mW it's not a fire hazard. It will fail open.
- USB-B for power was very intentional. It's a great firm connector and more importantly prevents users from plugging it into their piano wrong. Many of my customers are in their 70s or older.
- USB-A for data was made for manufacturing simplicity, but again, USB-C is too complicated for many of my users. I'd only switch to USB-C if both ports could be used interchangeably, but they can't be / it's not worth the complexity.
- As for the software moat, time will tell. You can't stave off competition forever!
500 units was my first run, and it worked out really well. None of the suppliers complained about that order size. I recommend starting with a smaller quantity until you've validated the market. The "economies of scale" between 100, 500, or 1000, units are not all that dramatic. Perhaps 30% cost difference.
I was originally planning to do 4000 units as my first run. Boy I'm glad I started to run out of money and cut it way back. That would have been way too much as a first run.
Not technically custom, but made to order (I gave them a spec sheet). If they had reasonably priced connectors on LCSC or DigiKey, etc, I would have used them!
Yes the anti-counterfeit is primarily app enforced (though entirely offline). I do use the firmware encryption features of the ESP32-S3, whatever that is worth, and the firmware is tied to the HSM.
The app is optional, and its for browsing your library. Think of it like the Photos app but for MIDI.