those switches per dot ratings are fair, but another assumption here is that EPD takes a non-0 amount of time to move the ink particles in the fluid they are suspended in with a magnetic field. when you try to move them more than roughly 8-12hz it already uses more power than a normal screen and if you run it at even higher voltages and speeds the ink particles start to burst and lose shape, leading to a greying out of the panel quite rapidly (within a few months)
"Typically, the energy required for a full switch on an E Ink display is about 4mJ/cm2. The corresponding number for the Rdot display is about 1mJ/cm2 with the addition of 0,25mJ/cm2 every 15 minutes. LCD continuously consumes about 6µW/cm2."
This is some interesting numbers. So, for a 1 cm^2 screen, LCD consumes 6mJ for every 1000 seconds - i.e. just over 15 minutes. But to redraw the screen on eInk takes 4mJ. So if you do something that would cause the screen to fully redraw more than twice every 15 minutes, then eInk actually consumes more power? But wouldn't that generally be the case while reading?
E-Ink displays were declared having a lifespan of 10 million switches per dot: you would have to do a study about how often the average pixel is changed, but if that value were 5s, the lifespan would be "five years of short week 9-to-5" - that is not bad.
I am not sure if A2 mode or Greyscale Update with frequent dot switching is a stress that makes the dots degrade faster (not simply "decrease the life count going towards the max", but "decreasing the max"). I supposed not dramatically.
>the current consumption was astronomical, sometimes triggering the protection of the power supply on certain images
That's surprising, since I was always under the impression that E-Ink displays were pretty low-power. Is it the drawing of the new image that requires so much energy in a small instant?
I held a colour 60Hz electrophoretic display a decade ago (first startup). Electrophoretic displays can go at very fast refresh rates if you just zap them hard enough (i.e. high voltage on the TFT). Without higher voltage they can still run fast but at the expense of losing contrast. You basically have little black and white "balls" (electrophoretic particles) travel up and down in the field (in those little e-ink cells). At conventional voltage the balls won't travel the full distance in a single fast image frame, so you won't get full black or full white. The problem is that people want colour, speed and low power consumption. Those are opposing requirements and E-ink made their bet on power (at the expense of colour and speed).
I admit I have a limited knowledge of E-ink displays, but having high refresh rates on E-ink monitors may cause ghosting, burn-ins and other undesirable effects.
> Realistically, the best you can do with e-ink is 1-bit with ~120ms refresh
I'm curious, why is that so? Can't the control algorithm boost the speed by sending higher voltages when switching, then going back to "holding" voltage?
> Is somebody able to explain why certain e-ink displays are so slow to refresh while others are much faster?
Sometimes it's the interface rather than the eink. The one in the article is a serial SPI interface. If the interface is parallel, instead it can be 8x, 16x, etc. faster
>Say you’re running an e-ink display that refreshes 60 times per second, is it still significantly more energy efficient than an LCD?
No.
E-ink displays are more efficient because if they refresh e.g. 1 time a minute instead of 60 times a second, then they are refreshing 3600x less often. Even if they took 100x more power per refresh, they'd still end up using 36x less power overall. It gets even nuttier when you go to e.g. refreshing once a day instead of 60Hz (60 * 3600 * 24 = 5 184 000 refreshes, over FIVE MILLION).
Please note that "e-ink" is basically a blanket term and contains a dozen different technologies (although almost all the screens that are actually sold at actual stores are electrophoretic displays), it's basically a genericized term based on E-Ink Corp so anything I say here is a sweeping summary.
1. E-ink requires a number of external components, even with their "chip on glass". In particular, E-ink requires a high voltage to change and charge the ink. I've seen inductors on most of these reference designs (ie: suggesting a boost converters of some kind).
2. E-Ink is very slow especially at this price range. Static images are fine, but don't expect animations.
3. E-ink protocols take a "temperature". In my cases, I've just been hard coding it to 25C / Room temperature, but this suggests that low-temperatures or high-temperatures may change the behavior of the screen.
4. E-ink is very "bursty" with power, using more power than LCD when changing images, but then zero power for most of its life. Be sure to think carefully about the current associated with this burst, especially if you're using small CR2032 coin cells (which have ~10 to ~100 ohms of internal resistance). A ~100mA draw on the charge inductor isn't out of the question (at 10-ohms, that's a voltage drop of 1V, which probably browns-out the RP2040). A slow-start circuit could solve this but you'd need to consider the longer charge times. Another method is to have 2x CR2032 cells in parallel, which lowers IR (parallel resistors lower resitance). I'd be most interested in studying the power-network of this design, I bet there's some interesting things going on here.
5. Most E-ink screens seem to be some kind of SPI protocol (4 wire). This is very similar to mini-LCD screens.
---------
LCD screens use more power, but get you color, more resolution, animation and seem to be cheaper still. Furthermore, LCD requires fewer external components (maybe a charge-pump set of capacitors, but some LCD screens don't even need that). Note that color/resolution/animation all costs processor power / storage / RAM, so be careful what you wish for.
LCD might be more suitable for beginners. But e-ink is very cool and awesome.
> What an incredible response time. I had no idea e-ink had advanced this much.
I'd urge caution. The video is misleading in my opinion as one can't see any detail, the lighting is dim. Look at 5:05. That's a 1 bit mode when moving.
As far as I know, there's been no improvement in fundamental performance of any display from electrophoretic vendors as the underlying limitation is due to physics! A2 mode is a trick, 1 bit dithered. And companies like Dasung have disclaimers in their manual basically saying that if you use A2 too long the panel may get damaged permanently. Eg:
"
aperlike Pro is more of a secondary monitor, which is mainly used for protecting eyes.
Instead of a photoelectric display, Paperlike Pro's display is based on ink droplets
movements, so lifetime limit is unavoidable. Any misuse may lead to Paperlike Pro's early
damage.
"
I'm one of the founders, E Ink displays have their display drivers on their glass substrate, meaning you would have a border that on a single key display would be too significant. We went with one large display with only one driving board for the entirety of the keys. This greatly reduced the unit cost to have one large EPD than 80+ small ones.
> Watching youtube isn't a good use case for a color e-ink
You may have not thought that part of the idea is using displays for education (video is an important format for educational material nowadays) in times where Countries are noting epidemics of eye difficulties (e.g. myopia) among students.
This said, use of video (frequent refresh) on EPD is strongly inefficient - EPD is energy-optimal as bistable, and consumes a lot upon state updates. And, those EPD cells are not eternal, they have a lifespan of state switches.
This is using an IT8951 EPD controller I wrote a little Rust driver for, which indeed talks SPI, although its SPI frontend is really a quirky/leaky abstraction over an I80 interface so you have to e.g. do chip select using I80 semantics and send preambles and such. Still, pretty breezy overall.
Can confirm the power draw is of course "bursty" during the update. Also, yes, e-ink refresh times get slower in colder temps. e-ink refresh also works poorly in direct sunlight. The displays can also "dry out" from it and it can cause artifacts. But the envelope for normal operation is overall fairly good, certainly for home/indoor use.
There's a fair amount of manufacturing tolerance and during testing manufacturers will usually record preferred drive voltages for the individual unit, etc. It's quite important to configure software to make use this information for optimal performance.
I'm hoping it will run for about a year without recharging from that little 1100 mAh LiPo pouch at one update a day (the newspaper is rendered on a common home server RasPi using LuaLaTeX+Ghostscript and then retrieved over Wifi), having taken self-discharge into account.
For more du-jour hype points I'm considering using OpenAI on the backend to summarize articles down to size to fit the layout! Or make it do style transfer to "1870 newspaper".
On top of that, while there are e-ink screens that can refresh at 30Hz, they aren't bi-stable. In other words, you have to give up the main benefit of e-ink in order to get half the refresh rate of a normal LCD.
The fundamental problem behind e-ink refresh rates is that there's an inherent physical limit to how quickly you can shake your ink particles up and down without damaging things.
reply