Electronics ideas: E-Ink clock

[Mark Robson]

Hi,

I'm sure many people have done E-ink clocks before, certainly ESP32-based wifi connected clocks seem to be a very common project. So I may have a go:

* If I can get a couple of black/white e-ink displays - they use no power when not changing, and can be updated in a couple of seconds (the colour ones look cooler but have a much slower refresh)

* I would like to make it completely solar powered with no battery. This means it won't be able to operate in darkness.

So questions

- Which ESP32 module do people use? I see there are rather a lot (AI-thinker and Espressif being the most common brands). The ESP32-WROOM-32D seems to be a popular one (other letters for variations) ? (I mean a castellated pins module that I can hand-solder easily, not the esp32-pico-d4 SOM which I used before and was a pain!)

- To program the esp32, we can use a serial/usb thing. Some models of ESP32 have built-in USB, but most don't. I know some people (Jeremy?) have built serial-usb chips into their project. I recently did a simple board with a WCH CH340C which worked very well (and very simple), but I haven't hooked up the RST / BOOT signals to a ESP32. Does anyone have an example of doing this? I know there is some circuit to control the reset/boot signals to allow the module to be programmed "hands free" from the computer without needing to hold down any buttons or short any jumper.

- On solar power - if I get a couple of 6V solar panels and put them in series - the panel should be able to put out maybe 100mA in full sunlight (maybe 50mA in a well lit room?) - any ideas for how to do this?

- Voltage regulation - the common two methods are linear regulator and switching regulator, but I notice that a lot of them (from the datasheet) have quite high quiescent current (e.g. up to 5mA) which is not ideal, as it could use up a lot of the power when the solar panels are not well lit. I am currently thinking of using a "low quiescent current" linear reg, for example the TI TPS709, which claims 1uA quiescent current. Is that a good idea?

- If I put about 16000 uF of capacitors on the output of the solar, according to my calculations it should be able to power the ESP32 for at least few seconds - long enough to connect to wifi, read the time and change the display - even if it happens to be in the dark during that period. 

Obviously the firmware will have to be reasonably clever to avoid using too much power and draining the capacitors down- it will need to spend a lot of time in sleep modes.

I definitely need to do some experiments with solar panels and capacitors to see whether the back-of-fag-packet calculations I've done actually work with real components.

Mark

[Vance Briggs]

(Some) Answers inline below:

On Fri, 24 Jun 2022, 19:13 Mark Robson, <mar...@gmail.com> wrote:

Hi,

I'm sure many people have done E-ink clocks before, certainly ESP32-based wifi connected clocks seem to be a very common project. So I may have a go:

* If I can get a couple of black/white e-ink displays - they use no power when not changing, and can be updated in a couple of seconds (the colour ones look cooler but have a much slower refresh)

* I would like to make it completely solar powered with no battery. This means it won't be able to operate in darkness.

Is a clock any use if you have no idea whether the displayed time is correct?

So questions

- Which ESP32 module do people use? I see there are rather a lot (AI-thinker and Espressif being the most common brands). The ESP32-WROOM-32D seems to be a popular one (other letters for variations) ? (I mean a castellated pins module that I can hand-solder easily, not the esp32-pico-d4 SOM which I used before and was a pain!)

I use the ESP32-WROOM-32D as a castellated stamp with no issues and I can be hand soldered. The gbd underneath is more difficult and I think on some design I have left it unconnected. Maybe an issue if you were drawing lots of power. 

- To program the esp32, we can use a serial/usb thing. Some models of ESP32 have built-in USB, but most don't. I know some people (Jeremy?) have built serial-usb chips into their project. I recently did a simple board with a WCH CH340C which worked very well (and very simple), but I haven't hooked up the RST / BOOT signals to a ESP32. Does anyone have an example of doing this? I know there is some circuit to control the reset/boot signals to allow the module to be programmed "hands free" from the computer without needing to hold down any buttons or short any jumper.

Check out the Adafruit circuit diagrams, they use RTS and DTR to control programming and boot

- On solar power - if I get a couple of 6V solar panels and put them in series - the panel should be able to put out maybe 100mA in full sunlight (maybe 50mA in a well lit room?) - any ideas for how to do this?

ESP can take over 500mA (spikey) when using wifi, your capacitors below may handle this though. 

- Voltage regulation - the common two methods are linear regulator and switching regulator, but I notice that a lot of them (from the datasheet) have quite high quiescent current (e.g. up to 5mA) which is not ideal, as it could use up a lot of the power when the solar panels are not well lit. I am currently thinking of using a "low quiescent current" linear reg, for example the TI TPS709, which claims 1uA quiescent current. Is that a good idea?

- If I put about 16000 uF of capacitors on the output of the solar, according to my calculations it should be able to power the ESP32 for at least few seconds - long enough to connect to wifi, read the time and change the display - even if it happens to be in the dark during that period. 

Obviously the firmware will have to be reasonably clever to avoid using too much power and draining the capacitors down- it will need to spend a lot of time in sleep modes.

Yep

I definitely need to do some experiments with solar panels and capacitors to see whether the back-of-fag-packet calculations I've done actually work with real components.

Mark

--
You received this message because you are subscribed to the Google Groups "rLab / Reading's Hackspace" group.
To unsubscribe from this group and stop receiving emails from it, send an email to reading-hacksp...@googlegroups.com.
To view this discussion on the web, visit https://groups.google.com/d/msgid/reading-hackspace/CAJ4NLMe%3DUhje6E3E1EX9MjZiFZEWb%2B9JwYAWdpiXC%2BGim4HuBw%40mail.gmail.com.

[Mark Robson]

Vance,

The idea is that the clock will show a placeholder image if it doesn't have enough power to update the time.

So if it's running out of power, the lights have just been turned out, it will display a picture of an owl or something.

I don't want it to show the wrong time, ever.

Mark

[Vance Briggs]

Oh, be careful about which serial adapter you choose if you want to automate program and reset. Not all of them expose both DTR and RTS.  This is the reset circuit from the schematic here https://learn.adafruit.com/adafruit-huzzah32-esp32-feather/downloads?utm_source=pocket_mylist

These ones have the extra pins broken out down the side of the board https://www.amazon.co.uk/XTVTX-FT232RL-Serial-Adapter-Arduino/dp/B09NRHWPQC

Vance

--
You received this message because you are subscribed to the Google Groups "rLab / Reading's Hackspace" group.
To unsubscribe from this group and stop receiving emails from it, send an email to reading-hacksp...@googlegroups.com.

To view this discussion on the web, visit https://groups.google.com/d/msgid/reading-hackspace/CAJ4NLMcwZ6xyGciXNhx3BLEJ0ua_cQ06ejyH5WkychQE1xcaeg%40mail.gmail.com.

[Gavin]

Can confirm that this circuit works for the reset. It appears to be the same as the one on the Adafruit Huzzah32 schematic hat I have successfully used.  

On operation in darkness, have you considered using a power scavenging IC and small LiPo instead of caps. Would likely  be able to run through the night. Would increase costs but then again larger e-ink displays are not cheap so once you’re in for that sort of money a few quid extra for something that works through the night worth it, no?

So let me know how you get on. I have been tempted to look at solar power for my e-ink temp sensors since you mentioned it on the call, but have so far resisted the scope creep in favour of banking Olathe work done so far 

G

To view this discussion on the web, visit https://groups.google.com/d/msgid/reading-hackspace/CAFLXuqtdSpLbapNCj_%3DuKLTbWvP8EM00sUfZ-jCXceeZkwx0dg%40mail.gmail.com.

[Gavin]

^ banking all the work done so far. No idea what Olathe means

[Gavin]

On time keeping, do any of the ESP32 modules have a low frequency time-keeping crystal incorporated? Otherwise might be worth considering adding one to the design as the drift on the ESP32 clock is high (I have seen reported as much as 5%) and unless you regularly resync via NTP (likely power expensive) you’ll get quite a lot of drift over the course of a day

G

[Bob Dunlop]

Hi,

On Fri, Jun 24 at 07:13, Mark Robson wrote:
> Hi,
>
> I'm sure many people have done E-ink clocks before, certainly ESP32-based
> wifi connected clocks seem to be a very common project. So I may have a go:

For a simple clock why do you need WiFi ? It's rather power hungry.

Why not use something like an MSF atomic clock receiver. [1]
Less than 100uA at 3V and then you could use a Cortex-M0 core to
crank the display and provide timing between turning the reciever
on periodically to check the base time.

Bet you could drive overnight consumption down into supercap territory.
A couple of AA's keep my large LCD MSF based clock running for years.

Just the first reference I found.

[1]
https://www.amazon.co.uk/60kHz-Atomic-Clock-Radio-Receiver/dp/B01KH3VEGS

--
Bob Dunlop

[Frank in Woodcote]

Yeah, I'll second what Bob said... Have a time keeping "thingy" that is super low power, like a I2C interfaced watch chip with 32kHz xtal and/or MSF receiver. That part of the circuit could be solar backed/charged or whatever to keep correct time. The display section could use as much power as it needs, even with LED for night use. And have another power source or extra solar to top that up. Or even use a water based battery, like those used on life jackets, just for interest.

[Mark Robson]

Sounds like a very good idea, the radio clock receiver thing. I had no idea they were so cheap / reliable (I remember Gavin's experiments a few years ago with them were inconclusive)

Yes I know I could use a rechargeable battery of some time and it would be no difficulty having it run through the night in a sleep mode, but I think it's more interesting to do without :)

Yes, wifi does use a lot of power so you need to turn it on sparingly.

I will definitely investigate the 32khz crystal thing if you think the esp32's normal crystal keeps lousy time. I assume the WROOM modules don't have one built in so you need to supply your own.

Mark

--
You received this message because you are subscribed to the Google Groups "rLab / Reading's Hackspace" group.
To unsubscribe from this group and stop receiving emails from it, send an email to reading-hacksp...@googlegroups.com.

To view this discussion on the web, visit https://groups.google.com/d/msgid/reading-hackspace/YrcamIavQAeGC3zR%40xyzzy.org.uk.