Finally...  the PCB's arrived and they look awesome.

Everything worked straight away, much to my surprise.  I've never used ePaper prior and although the driving circuit for it was rather straight-forward, I couldn't really verify it would work until the PCB's came and were built.  Thankfully, nothing blew up or otherwise.

Power consumption at this point (still need to do a lot with the firmware), is about 57 micro-amps during sleep.  As I anticipate only waking things up every 10 minutes or so to take measurements and update the display, two AA batteries will keep this thing running for quite some time.

I did mess up a few things, however.  The FPC connector is too close to the edge of the board and needs to move a millimeter or two deeper; when the ePaper is folded over the board, the contacts on the cable are bending, which probably isn't great.

Also, the gas sensor, the SGP41, may need to be reconsidered...  which is unfortunate.  Sensirion has a nice library that you can send the returned values from the sensor to and it spits out a VOC and NOx index values.  Awesome... except that the datasheet then states, "SGP41 raw signals need to be provided to the Gas Index Algorithm at a sampling rate of 1 second."  Not great...

Seems like they really want this sensor to be operating continuously; not intermittently.  I missed this point prior to picking the SGP41 when skimming (yep, guilty) the datasheet...  and it was a rather important point.  Ah well.  I still get what appears to be valid results, but as I'm not doing it by-the-book, I don't know how much accuracy I'm throwing out the window.

After messing around with this and nailed down the firmware a bit more, it'll be on the revision 2.