This particular external RTC has very low power draw, and it allows me to put the esp32 into a deeper sleep state and turn off the entire RTC and RTC memory mini-MCU in the entire esp32. It does make a difference.
> I assume you added it because the e-ink hat has no proper shutdown. From the looks of it you can just bypass the BUCK converter on it so just run it off 3.3-3.6v. There is a smaller BOOST converter in there that might still waste power so the mosfet might still be n
Aye, the controller board isn't designed for a battery-based application and has an idiotically high idle power draw, even not taking the always-on power LED into account I could have taken out, so I'm only powering it up to do the update.
And yeah, I'm sure a MOSFET would do this fine.
> Anyway 9-10 months is remarkable for the LEGO approach.
The LEGO approach is partly because I kept shifting the goal posts - originally I wanted to forego controller board entirely, and directly drive the e-ink waveforms from the MCU with the help of an op-amp (there's some prior art and reverse engineering available for this). This is partially why I picked a dev board with a big external PSRAM for a trial run. The controller board has its own SPI memory to hold the large framebuffer, but I was originally going to park this with the esp32 and have the lob of memory hooked up there :-)
My other plan was actually ordering a custom PCB that has it all in one place (this is the main reason why I didn't bother to solder anything to a perf board).
But then I had a little daughter and plans changed, so I shipped the mockup to production. Since it's holding up pretty well I'm quite happy with how it turned out anyway, but I absolutely agree a cleaned-up "v1.0" of this thing would be really nice to do at some point.
Also, do note that I'm mainly a software engineer and have no formal training or background in EE, so partly I do these as little hobbyist learning projects and to do something with my hands. If your day consists of Alt-Tabbing between your EDA and your Mouser/Digikey order tracking I'm sure you'd approach this very differently and iterate it much more on the screen first :)