Can someone explain how this really works?

http://www.eink.com/images/how_eink_works_anim.gif

I don't understand those bubbles, and how you get different colors on this type of screen, or it is only black&white, does it works similar to capacitive and resistive cellphone touch displays? How they display shades of gray?

  • All in all, it's awesome – OverCoder Jul 28 '15 at 16:26
up vote 11 down vote accepted
+50

How does a newspaper display shades of grey? They don't have 10000 different colours ink do they?

Get a magnifying glass and see: They put black dots in groups, many dots are dark, few dots are light.

That's exactly how this works. One such bubble can only be black or white, but because there's 100's of them in a square cm they can turn on only a few to get greyscales. In older e-Ink displays you could still see that if you looked up closely. Probably in the cheaper types still can. The grey background is just a mess of more and less dense black dots if you put your nose right up to the screen of a lower resolution one.

Further the system works pretty much like it is displayed in the animation. Much like a pre-charged electret microphone the bubble and plates are very well isolated, so that a charge cannot easily escape, so are the pigment granules. Probably some form of epoxy micro-droplets with charged particles inside, so that the particles can't mingle and neutralise.

That way an e-Ink screen can stay "charged" for years, or possibly decades, before it starts to fade and eventually stops working.

Because you only need a little current when changing a pixel to change the charge on the plate, the display can work powerless as long as the picture doesn't change for days, weeks or in higher end models even years.

EDIT:

Of course where I mention "one bubble" it should be "one set of electrodes". One bubble can have 1, 2 or 4 electrode pairs I believe, the animation shows it for 2 electrode sets per bubble as well. So by having 4 top and 4 bottom electrodes a bubble itself could contain 4 black/white pixels, making it a 4-level grey-scale pixel in itself. But one set of electrodes can always only make black or white, nothing in between.

  • 3
    What if there were 50 electrode sets? Would you then have 50 shades of gray? – dberm22 Jul 28 '15 at 14:16
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    @dberm22 Technically. Yes. But, then you can also just use 50 pixels. Or a 100 for twice as much excitement. Or even 1000! Think of that! (But not in the boss' time) – Asmyldof Jul 28 '15 at 14:35
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    @Asmyldof: I think dberm22 was making a joke – Johnny Jul 28 '15 at 17:25
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    @Johnny I know, why else would I add "But not in the boss' time" after "think of that"? ;-) – Asmyldof Jul 28 '15 at 18:21

How do you get different colors on this type of screen, or it is only black&white?

It's black and white only.

Does it works similar to capacitive and resistive cellphone touch displays?

Capacitive and resistive are types of touch sensor. The touch sensor and screen are different technologies and separate parts. The normal cellphone display is LCD with a backlight, although some are OLED. You can put a touch sensor on an e-ink display - the Kindle does this.

Edit in response to comments: apparently there can be color "e-paper" which is not the same as "e-ink", because Sharp like having a confusing trademark. http://www.sharpmemorylcd.com/aboutmemorylcd.html : Memory LCD is literally an LCD with a memory at every pixel, rather than the single transistor normally present on a TFT. That allows TFT-like properties without requiring continuous refresh. It's also constructed in "transflective" mode, ie in front of a mirror rather than a backlight.

  • Actually, color e-ink exists (e.g. Pebble Time). I don't know if the technology is all that similar, but "it's black and white only" seems misleading at the least. – Jasper Jul 28 '15 at 12:58
  • This particular one is black and white. How does the pebble time one work? The internet is not very helpful. I can see eink.com/display_products_triton.html which suggests that it's a monochrome hi-res display with a color filter over it. – pjc50 Jul 28 '15 at 13:09
  • That makes sense, actually. The Pebble Time only supports 64 colors (compared to Aurora's 4096) whereas Triton uses a similar technology as in the picture to display 3 colors, so it's not quite clear what technique it uses. Thanks. It might make sense to add that to the answer (something along the lines of "The setup shown in the image is for black & white only. Colors are possible through both similar and different techniques, but the exact specifics aren't public knowledge at this time.") – Jasper Jul 28 '15 at 13:42
  • I would assume (also @Jasper) that a colour e-Ink display would use a process similar to CYMK, where the number of perceptible colours is a result of the number of blobs inside an "optical pixel". Again, much like in print. – Asmyldof Jul 28 '15 at 14:38
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    The pebble time does not use color e-ink. It uses the confusingly similarly named color e-paper, which is in fact a marketing name for Sharp's "memory LCD" technology. It is a special kind of transflective LCD with built-in memory, so the processor does not have to regularly refresh the whole screen. While it shares some properties with e-ink, it does not use electrophoresis or black/white microparticles. – Michael Karcher Jul 28 '15 at 14:59

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