I'm still trying to get to a secure feeling about the use of a piezoelectric microphone, in the form of a throat mike. I've seen several takes on electronics to adjust the feed, ranging from complex circuitry that would require another breakout board to a single resistor. I've decided to go with the latter (at 1MΩ) for now, though I'll be asking a few more people about it; I suspect that the final answer will be somewhere in between.

The problem I have with the more complex schematics I've seen is that they're set up for higher voltages (9V and up); assume positive and negative leads as well as Ground; or both. All I have to work with here is 3.3V, and maybe 5V, as well as Ground. Probably the layouts with just higher voltages could translate easily enough to 3.3V; the ones that ask for negative-voltage power separate from Ground, not so much.

Whatever the end result, it'll be user-selectable with a solder jumper. (Yeah, if I have my way, half the underside would be covered in solder jumpers. I like to maximize options.)

Also, speaking of Ground: in working on a good layout for including the ground plane, I've found a few redundant and/or excessive traces for the ground in the circuitry. Fixing those has made a few other traces easier to work with.