The mk2 circuit boards are here, and I'm happy to report that the power regulation and battery charging circuits work great! With a bit of tribulation surrounding the fact that I lost my SWD programmer and had to rig one up using a raspberry pi (advice: just don't. it's a huge headache. an st-link v2 is like $10), I was able to load code onto the nrf52840. I forked Adafruit's bootloader for this chip and updated the board definition mine, here.

Unfortunately, that's about where the good news stops. I couldn't test most of the rest of the board, because I ordered the wrong footprints for the flash chip, RTC chip, and most of the diodes surrounding the epaper display... but it programs!

I'll be putting together a rev2 of the board with the following changes:

• Switching back to the Memory LCD, which requires a 5V boost regulator
• Removing the physical "bootloader mode" button, since double-tapping reset works
• Fixing the footprints for the Flash and RTC chips
• Adding a max17262 fuel gauge IC, to track the battery level
• Putting the SWD pads in a more uniform layout, so I can use a pogo pin adapter to flash the board for the first time instead of soldering jumper wires to test points
• Physically changing the layout a bit to better fit the memory LCD

I'm also going to be redoing the layout of the github repository (and likely break it up into several subrepos), since right now it's kind of a mess.