E-paper on batteries

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martinus
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E-paper on batteries

#1 Post by martinus » 31 May 2020, 13:24

While a normal LCD would draw current al the time, an E-paper display should retain it's picture without any power.
To do some experiments, i've ordered a Wemos E-paper display to see if this can be run on batteries for several months.

Unfortunately, the display refresh takes up to 2 seconds, but during that time, the ESP radio is no longer needed. So the ESP uses ESPNOW to retreive a value from another ESP unit, power down the radio so it consumes approx. 20 mA and then do the display update and finally total power off.
The sleep current is 17 uA. This way a useful battery life could be established if my calculations are in order.

I've mounted a 20-pin header to the module so almost all GPIO pins are now exposed for connecting things like this e-paper module:
e-paper.png
e-paper.png (460.66 KiB) Viewed 2817 times

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Ath
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Re: E-paper on batteries

#2 Post by Ath » 31 May 2020, 14:39

Great results so far!

Btw: Are those numbers anything real, like from a PV installation, or just something random?

TD-er
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Re: E-paper on batteries

#3 Post by TD-er » 31 May 2020, 15:27

Some of these displays also support partial updates.
Maybe that can shorten the refresh time?
For this you may want to draw a separation line around the area to refresh, or else the neighboring pixels that are not meant to change may (literally) rotate slightly when you alter the pixels next to it.
With a dark line at the edge of the updated area it is less noticeable you also affect the neighboring pixels.

And for even lower power consumption in deep sleep, see: https://www.youtube.com/watch?v=n_A_8Y4xNx8 (not tested myself)

martinus
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Re: E-paper on batteries

#4 Post by martinus » 02 Jun 2020, 17:02

TD-er wrote: 31 May 2020, 15:27 Some of these displays also support partial updates.
Maybe that can shorten the refresh time?
Not sure if that will work when everything is powered off between cycles?
TD-er wrote: 31 May 2020, 15:27 And for even lower power consumption in deep sleep, see: https://www.youtube.com/watch?v=n_A_8Y4xNx8 (not tested myself)
That does not apply to the LSC sensor as it does not use deepsleep on the ESP module. It's powered off after use.
Right now, the 17uA is combined current use of both the Tuya MCU and the ATTiny85.

martinus
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Re: E-paper on batteries

#5 Post by martinus » 02 Jun 2020, 17:03

Ath wrote: 31 May 2020, 14:39 Great results so far!

Btw: Are those numbers anything real, like from a PV installation, or just something random?
The upper value is the controlled servo position (not used here) and the lower value is the battery voltage. Just for testing...

martinus
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Re: E-paper on batteries

#6 Post by martinus » 02 Jun 2020, 17:08

I'm planning to use an e-paper inside a picture frame, running on batteries. The bigger display has arrived and it's also running with some test values, this time inside/outside temperature and the battery voltage:
WaveShare.png
WaveShare.png (1.86 MiB) Viewed 2740 times
This setup uses an enhanced Pro Mini Extender connected to I2C bus.

All stuff should fit behind the display and tucked away in another Ikea picture frame when proven stable.

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Re: E-paper on batteries

#7 Post by TD-er » 02 Jun 2020, 22:12

martinus wrote: 02 Jun 2020, 17:02
TD-er wrote: 31 May 2020, 15:27 Some of these displays also support partial updates.
Maybe that can shorten the refresh time?
Not sure if that will work when everything is powered off between cycles?
[...]
If the e-ink display does a full update, based on stored image data, then it will not work between power cycles.
But then the update time would be the same as when doing a full screen update.
However the update time is a lot less when doing partial updates, so that would suggest it is actually only updating a part of it.
I also don't think it will invert the pixels first (needed to prevent 'ghosting' of old images), to achieve this faster update.

Not all e-ink displays support partial updates, so you need to check if your module supports it.

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