Congratulations, it's funded ![ThumbsUp :-+](https://www.eevblog.com/forum/Smileys/default/icon_smile_thumbsup.gif)
Thank you guys for your support! I was contemplating between 7-8 week campaign period, and went for 7 weeks only because I wanted to make sure I can ship before December (to avoid Christmas season where shipping delays go out of control), but I'd have never imagined the project gets funded in just two and a half days. I'm so glad and thank you.
I've read your update on safety. I think it's a good idea to add to the discussion one more case - negative voltages. If they poke a ground wire into VIn then there will be negative voltages on other pins.
Good point to bring this up too. The ESD diodes were chosen to be bidirectional for exactly this reason. If you connect your data lines before the power, and you reverse the polarity on power, then your data signals may be negative. Unidirectional diodes would start conducting and your own board's digital outputs would see it as a short, so there's a good chance your application would burn down. Bidirectional diodes avoid this short, but now the muArt will probably get damaged instead. This is however the more preferable way, because I'd rather protect the application circuit. You may not have a replacement for your custom circuit at hand, but a UART adapter is easily replaced. The adapter is also probably way cheaper than whatever circuit is hanging on its IOs. So, for both of these reasons, if I have to choose which to preserve like in this case, I'll save the application.
Of course, if you connect power first and only then the data lines, the picture looks different. As I've mentioned in my earlier post, I've made the power LED light up only when power on *both* sides of the muArt have been correctly applied. This means you can immediately recognize if the VIN polarity is wrong (LED won't light up), so you can correct it before attaching any IOs, and all is good.
EDIT: I've incorporated these points into the original article, but I need CrowdSupply to publish the changes. They'll probably do it after the weekend.