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sho_hnHNSource author
Lessons learnedExperience excerpt · English

> but the external wakeup has no real advantage in power draw

> but the external wakeup has no real advantage in power draw. 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. …

Original discussionE Ink’s color ePaper tech gets supersized for outdoor displays145 source comments · at import
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blkhawkHN

I made my own version of this and I am seeing a lot of interesting choices so I am intrigued. The lack of soldering means you probably don't do that normally. I find it wild that you used a dev board because the LDOs on them are most of the time very bad and you do seem to use 5V instead of bypassing that. The type you get normally uses 1mA just sitting idle. Why did you use an external RTC instead of just soldering a 32.768khz crystal to the esp32? Okay if my assumption above is correct that answers that. but the external wakeup has no real advantage in power draw. The relay eats some current and a mosfet in its place would probably be better. 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 mosf…

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generjHN

If it helps, I went for the elegant all in one PCB version (dutifully replicating the e-paper driver schematic from Waveshare). I had to learn a fair bit about how to specify inductors (not something my similarly basic EE background covered much of). I somehow put a short on the design so my JLCPCB PCBA order is worthless. The short only appears when soldering the ESP32 down and I’ve tried three different boards with three different ESP32 C6 modules and it’s present in all of them. I would have been much better off prototyping with LEGO parts first.

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blkhawkHN

RE: the external clock - in my setup I got the power draw down to ~24µA with just a crystal but its possible that a completely external wakeup could be lower. Not that i think it makes a difference with that dev board :) You inspired me to redo mine since I saw a new type of colour e-ink display (Spectra C6)

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