4 ms·

For the most part I've found that RaspPis are over-dimensioned for many projects I'm inclined to do, for example around the house, and have switched to much mor

by sho_hn 4y ago

For the most part I've found that RaspPis are over-dimensioned for many projects I'm inclined to do, for example around the house, and have switched to much more readily-available and cheaper ESP32 and STM32 boards. I do have a RasPi in use that runs some heavier software like a Hue bridge emulator written in Python (diyHue), and for some of my projects I now have that Pi do more intensive computation centrally and then just dispatch results to esp32s. I'm currently building one of those refresh-once-a-day framed e-ink "newspaper on the wall" projects. In the picture frame I just have the panel, an IT8951 display controller and an esp32, all running off a LiPo pouch, mostly in deep sleep. The RSS scraping and pdflatex+ghostscript pipeline to produce the image is running on the central Pi in this. A single Pi may be all you need if your projects live on a network!

knodi123 4y ago
How much time can you get off a lipo pouch? If it's "on the wall", why isn't it powered by an ac adapter?
- sho_hn 4y ago
  > How much time can you get off a lipo pouch? Time will tell, but I'm hoping for at least a couple of months on a 1100 mAh. Napkin calculations had me at 6-7 months. It's e-ink, so I can shut down the entire display and controller after the refresh, and the ESP32 is in deep sleep until it wakes up on timer and performs a network fetch and display update, then back to sleep. > If it's "on the wall", why isn't it powered by an ac adapter? Effort :-) It's a picture frame on a wall, I don't want to have an externally visible cable going into it and burying a cable in the wall is more work than all the rest of it.
  - knodi123 4y ago
    Wow, I'm not used to thinking of batteries in those terms. If you hit 3 months, you deserve to crack a bottle of champagne, that's a really impressive bit of engineering. Although now that I think about it, smoke detectors have been lasting a year on a 9-volt for all my life, so maybe I'm just short-sighted. :-)
    - sho_hn 4y ago
      An ESP32 just draws about 0.15mA or less in deep sleep mode, even less if the ULP co-processor is turned off - down to about 5 µA if you're willing to keep no state/data around and just need timer wakeup. That's 220000 hours of hibernation on an ideal 1100 mAh battery (i.e. one that doesn't lose charge by itself over time)! In practice this is unattainable, because batteries are not ideal, and there's quite some efficiency loss from e.g. voltage regulators. But you can realistically get to years of hibernation. Of course the power draw is much higher if you e.g. need to permanently keep a WiFi connection open and can't sleep (there's lower-power alternatives to WiFi like ESP-NOW for some applications), but I just need a connection for a very short time to fetch a 1600x1200x4 image. And to power a full display refresh on the e-ink panel. If you think about it, a Kindle or similar also runs for days to weeks off a single charge, and that has a lot more interaction and computation going on during use, a more powerful processor with higher power draw and it sleeps less deeply and for shorter time. My application is suitable to extend beyond that by a large factor.
madaxe_again 4y ago
Yeah, I have a single 4b doing everything from openhab to shinobi to LoRA bridging, MQTT brokering, VPN termination, DNS, routing, pretty much anything where I need a Linux box to do a thing - we live off grid, so having a handy utility server that uses very little power is dead handy. Plans to get another, as some redundancy would be good and it strains transcoding video, but you can pile a surprising amount onto one.
dividedbyzero 4y ago
What panel are you using?
- sho_hn 4y ago
  This one: https://www.waveshare.com/product/displays/e-paper/epaper-1/13.3inch-e-paper-hat.htm https://www.waveshare.com/product/displays/e-paper/epaper-1/... 13.3", the largest I could afford :-)
  - aliqot 4y ago
    That's so cool. Did you build this from instructions somewhere or just using your imagination and seeing what works? Perhaps a build log article maybe?
    - sho_hn 4y ago
      My inspiration is this: https://www.youtube.com/watch?v=gECj1AE9D2c https://www.youtube.com/watch?v=gECj1AE9D2c But I actually only watched the first 30 seconds and then got hooked on the idea. The impl is mine :-)

by sho_hn 4y ago

knodi123 4y ago

How much time can you get off a lipo pouch? If it's "on the wall", why isn't it powered by an ac adapter?

sho_hn 4y ago
> How much time can you get off a lipo pouch? Time will tell, but I'm hoping for at least a couple of months on a 1100 mAh. Napkin calculations had me at 6-7 months. It's e-ink, so I can shut down the entire display and controller after the refresh, and the ESP32 is in deep sleep until it wakes up on timer and performs a network fetch and display update, then back to sleep. > If it's "on the wall", why isn't it powered by an ac adapter? Effort :-) It's a picture frame on a wall, I don't want to have an externally visible cable going into it and burying a cable in the wall is more work than all the rest of it.
- knodi123 4y ago
  Wow, I'm not used to thinking of batteries in those terms. If you hit 3 months, you deserve to crack a bottle of champagne, that's a really impressive bit of engineering. Although now that I think about it, smoke detectors have been lasting a year on a 9-volt for all my life, so maybe I'm just short-sighted. :-)
  - sho_hn 4y ago
    An ESP32 just draws about 0.15mA or less in deep sleep mode, even less if the ULP co-processor is turned off - down to about 5 µA if you're willing to keep no state/data around and just need timer wakeup. That's 220000 hours of hibernation on an ideal 1100 mAh battery (i.e. one that doesn't lose charge by itself over time)! In practice this is unattainable, because batteries are not ideal, and there's quite some efficiency loss from e.g. voltage regulators. But you can realistically get to years of hibernation. Of course the power draw is much higher if you e.g. need to permanently keep a WiFi connection open and can't sleep (there's lower-power alternatives to WiFi like ESP-NOW for some applications), but I just need a connection for a very short time to fetch a 1600x1200x4 image. And to power a full display refresh on the e-ink panel. If you think about it, a Kindle or similar also runs for days to weeks off a single charge, and that has a lot more interaction and computation going on during use, a more powerful processor with higher power draw and it sleeps less deeply and for shorter time. My application is suitable to extend beyond that by a large factor.

madaxe_again 4y ago

Yeah, I have a single 4b doing everything from openhab to shinobi to LoRA bridging, MQTT brokering, VPN termination, DNS, routing, pretty much anything where I need a Linux box to do a thing - we live off grid, so having a handy utility server that uses very little power is dead handy. Plans to get another, as some redundancy would be good and it strains transcoding video, but you can pile a surprising amount onto one.

dividedbyzero 4y ago

What panel are you using?

sho_hn 4y ago
This one: https://www.waveshare.com/product/displays/e-paper/epaper-1/13.3inch-e-paper-hat.htm https://www.waveshare.com/product/displays/e-paper/epaper-1/... 13.3", the largest I could afford :-)
- aliqot 4y ago
  That's so cool. Did you build this from instructions somewhere or just using your imagination and seeing what works? Perhaps a build log article maybe?
  - sho_hn 4y ago
    My inspiration is this: https://www.youtube.com/watch?v=gECj1AE9D2c https://www.youtube.com/watch?v=gECj1AE9D2c But I actually only watched the first 30 seconds and then got hooked on the idea. The impl is mine :-)