I'm curious about the level of expertise you need in order to do this. I also have a cheap bracelet and I wanted to do the same thing, but reading this article seems like you need to be an expert in electronics/lowlevelprogramming.

Hi, author here. I can honestly say that I’m definitely not an expert. I tried to systematically write down questions on a text file and solve them one after the other. Solving one usually added a few other ones. “What chip is this?”, “how to program this chip?”, “do I need a development board?”, “what’s SWD?”, “how to pull an output high?” Etc. Lots of these are specific to this chip, too, so a lot of it is just reading the documentations and drilling down on libraries.

It’s something I find refreshing to read and like to state when I can: none of this was easy for me. But it was definitely fun. Having no deadlines helps. Having no practical goal and just enjoying the process was also refreshingly nice.