Some quick notes on The Open Book at end of year. First: after a lot of people asked about donations, I made a Patreon page where folks can support the work. But whatever, on to the work itself: rev 4 was a success! The new features (mic shutdown, VBUS monitor, battery full LED) work as expected, and I've updated the Arduino core and the Open Book library with support for the new pinout. I also designed a basic 3D printed enclosure and another in laser-cut wood. Both are compatible with both the Open Book board and the eBook Wing (by rotating the back piece 180 degrees).

I've expanded the custom e-ink driver I've been writing with waveforms for quick refresh, grayscale mode and partial refresh. Improving partial refresh is a TODO item; my current waveform causes temporary ghosting after a while, and I worry it may have negative long-term effects. But I sense that if I add an invert phase to BB and WW it will improve things (at the cost of a little bit of flickering).

Oh! I also trained a TensorFlow Lite model to recognize voice commands on the inline mic, to show my current thinking for future accessibility work. Gives good demo, even if it has trouble with the word "left". 

That's accomplishments. Now, a couple of challenges:

• I have noticed a little bit of noise on the mic input when plugged in to USB power, and I think it has to do with the way I'm connecting the USB shield to the ground plane. When I do a revision for manufacturing, I will want to add an RC filter between the USB shield and the ground plane.
• The right-angle buttons for previous and next page feel superfluous, and they're hard to press when the board is in a case. May omit them in the future, since they're relatively pricey.
• On a couple of boards, the Lock button fell off after a while, which tells me there's a mechanical issue there. For now I'm just applying a bunch more solder to keep the right-angle buttons secure, but I need to find some buttons with pegs to alleviate the stress of repeated pressing, or devise some other method for supporting them.
• I'm evaluating some very tiny white right-angle LED's in the hopes of perhaps implementing a front light, though there are some challenges there.

Thanks, everyone, for your kind words and support, and happy new year! See you in the new decade.