E-paper test - Page 1
Forum section: electronics / projects

author: FrankBuss
author_rank: Unknown
timestamp: February 04, 2014, 08:41:51 am
content: I bought an 2.7" E-paper Display Module from Embedded Artists, and tested it with a Raspberry Pi:http://www.frank-buss.de/raspberrypi/epaper/index.htmlAnd no, it's not just a printed label stuck on the display, it's amazing, it really looks very much like real paperThe resolution is 264x176 pixels for this model. The update rate of the display is a bit slow: With the demo app about 3 seconds to remove the old image (the demo program first shows the inverted old image, then full white, then the inverted new image and then the normal new image, to prevent ghosting). But partial update is possible with a better library on the Raspberry Pi. And the best feature: it maintains the image without power (datasheet says for several hundred hours).Any idea what I could do with it? I was thinking of a weather station, with temperature, air-pressure, and relative humidity. With a small PIC and a coin cell, and an update rate once every some minutes it would last forever. But it is kind of a boring application, you can buy this already (albeit not with such a nice display).At Glynstore there are even a 1.44" version, which costs just EUR 8.21 for single quantities. You'll need the flex connector, some passive components, and some small signal FETs, but I guess total cost could be less than EUR 10 to add such a nice display to one of your projects.I'm not related to Embedded Artists, Glynstore or Pervasive Displays, just an exited customer.

author: Rerouter
author_rank: Super Contributor
timestamp: February 04, 2014, 10:16:03 am
content: a quote of the day system, waking up for a few seconds at the start of every day, reads in a famous quote from an eeprom, writes it the the display then goes back into deep sleep?

author: jwm
author_rank: Regular Contributor
timestamp: February 04, 2014, 10:50:55 am
content: As an idea for something to do with it..Something I wanted when out in the desert recently was a robust volt/amp/power meter that could be read in direct, bright sunlight and can handle a lot of abuse and show a graph of recent power usage. I work on art installations at burning man which take a lot of abuse, being able to walk by and see at a glance independent of time of day or dust storm things are okay or that I have enough power to make it back to camp would be great. During the day it is too bright to read many displays and at night you have a forehead flashlight maybe that also doesn't play nice with them, no nice diffuse room lighting.My brute force one I built for next year is thishttps://picasaweb.google.com/lh/photo/ijJ9wSxRLkgnRShOTdGNjtMTjNZETYmyPJy0liipFm0?feat=directlinkbut it isn't entirely all that and only good for instantanios monitoring.It would be nice to have power in addition to volts and amps and the ability to raise an alarm if things go out of limit. I was thinking your e-paper behind some perspex connected to a uC and aLTC2945would do it. Having a graph of power usage over the last couple hours would be good too.John

author: amyk
author_rank: Super Contributor
timestamp: February 04, 2014, 12:37:51 pm
content: This related thread may be of interest:https://www.eevblog.com/forum/reviews/txtr-beagle/tl;dr: repurposing display from an ultra-cheap eBook reader.

author: FrankBuss
author_rank: Unknown
timestamp: February 04, 2014, 03:01:53 pm
content: Quote from: jwm on February 04, 2014, 10:50:55 amGood idea. It could look like this:(this was the source image:http://www.frank-buss.de/raspberrypi/epaper/energy-monitor.png)The inverted graph is easy to read. For the retro-electronics fans an, some old style analog voltmeters could be simulated. Bright ambient light is no problem for the display and should be possible to read with a forehead flashlight as well.The LTC2945 is expensive. I think with some external circuits and maybe some calibration, the ADCs of a microcontroller would be sufficient for such an energy monitor.

author: FrankBuss
author_rank: Unknown
timestamp: February 04, 2014, 05:29:03 pm
content: There is a problem with the energy monitor when the battery is empty (I think it should have a battery, to record 0 V), because the last display update would be always visible. Maybe I could measure the battery voltage and then display a text "low or empty battery" (above the normal image, so that at least some logging history would be preserved) and stop the microcontroller at some lower limit voltage level. But then the user still don't know, if the battery is just low and the thing is still working, or if the battery is empty. Interesting new problems with this kind of display

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: February 04, 2014, 05:51:02 pm
content: I like these e-paper, e-ink, etc. displays. I saw a vid where they drilled holes into one and folded, etc. It still worked. I'm surprised that they have not shown up in meters. I wonder if it's due to low light situations. I'm not sure how e-paper displays are lighted. Side mount leds might work but they look bad usually. Maybe it's just the refresh rates are too low. Do you know the limiting factor in the refresh rate? Might require more expensive e-paper for high enough rate to do 4/second like on a fluke dmm for example. I looked at a datasheet and could not decipher any refresh data.

author: FrankBuss
author_rank: Unknown
timestamp: February 04, 2014, 06:23:21 pm
content: Right, the datasheet of the display itself could be better. But there is a description of one of their dev boards:http://www.pervasivedisplays.com/_literature_112691/Developer_Guide_for_Demo_Kitand it says execution time for a display update is 2.6 seconds (page 9). This is close to the 3 seconds I measured with my stop watch.It gets more interesting if you implement your own partial update functions, because the display allows to update single rows individually and each pixel is 2 bits: on, off, don't change. Then there is a busy signal when the row is updated. I guess with some clever programming and lots of "don't change" bits it could be a lot faster, at least for small areas.But I guess it would be still too slow for multimeters. The lighting should be no problem: It really has all features of paper. View angle is no problem (as sharp and clear from nearly 90° from all sides as from top) and I can still read it in dim light conditions, when I can't read my (non-backlighted) LCD multimeter. A LED mounted somewhere on top or bottom side of it should be sufficient, you know, like the lamps in those old analog meters. I guess it would look very much the same.

author: komet
author_rank: Unknown
timestamp: February 04, 2014, 06:28:56 pm
content: Does anyone make e-paper displays that aren't tiny? I want one at least 7", ideally up to 30". Does anyone know of sources?

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: February 04, 2014, 07:11:58 pm
content: @FrankBuss,You're right the LED side-lights might be fine, but maybe have enough to eliminate or reduce the dark areas. Maybe diffuse the bright spots would be enough.I have a ebook reader that uses e-ink and I don't use it to buy books I use it to view pdfs from the internet so when I got it it would only allow connecting to B&N but of course there was a work-around. Long story short I rooted the nook (very, very simple) and one thing I remember while researching doing this was that someone had gotten a video game to run on this device but I don't recall the refresh rates they got but they tweaked something to enable better refresh. I will try to find more data.

author: Bored@Work
author_rank: Super Contributor
timestamp: February 04, 2014, 08:49:09 pm
content: Quote from: GiskardReventlov on February 04, 2014, 05:51:02 pmIt is a safety issues. You can not discern if a meter showing 0 V indeed measures 0 V or if it is just broken and there is in reality a high voltage.Someone might figure out a trick to reliable fix this in the future. Or some manufacturer will just give a flying fart about safety and do it anyhow.

author: FrankBuss
author_rank: Unknown
timestamp: February 04, 2014, 10:14:37 pm
content: The safety problem could be a problem for my energy monitor as well. Would it be sufficient to declare it as "CAT I" and just allow low voltages for it?A workaround would be to implement some kind of clock, or a blinking dot. If the dot is no blinking, then the display doesn't show the current value. But this might be difficult to argue with safety people and somewhat surprising for the user. Maybe an additional note with a big warning under the dot (printed on the case outside of the display) which explains the function of it.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: February 04, 2014, 10:47:26 pm
content: This watch uses e-paper:http://www.sonostar.com/When the battery goes dead do they blank the display or show the wrong time? I hope they blank the display.BTW the trick they used (in my previous post) was reduce to 1-bit display, so just black and white, no grey scale. So maybe that's a solution for one part of the problem for e-paper display on DMM .

author: FrankBuss
author_rank: Unknown
timestamp: February 04, 2014, 11:23:31 pm
content: Nice watch, at least what I can see in the renderings and the video, they don't ship it yet. But a watch where the display just freezes when the battery is empty wouldn't be useful, especially with e-papers, because there might be not much animation on the display when it is running. Needs some tick-tack like an old wall clock or analog wrist watch. Then you can listen to it if it still ticks.

author: jwm
author_rank: Regular Contributor
timestamp: February 05, 2014, 12:34:29 am
content: Quote from: FrankBuss on February 04, 2014, 05:29:03 pmFor the energy monitor, I'd want an additional battery for the monitor itself, to allow it to monitor down to zero volts. the LTC2945 is easy to run off an external supply in addition to what it is monitoring. They will sample the chip for free. I have a few I have been meaning to turn into usb power monitors. It has 3 really nice 24 bit ADCs that can take simultanious measurements (unlike atmegas say that time share a single ADC) and a hardware multiplier for power. It's a really neat chip.

author: FrankBuss
author_rank: Unknown
timestamp: February 05, 2014, 07:34:49 am
content: Quote from: jwm on February 05, 2014, 12:34:29 amThe datasheet doesn't say anything about simultaneous measurements, see the block diagram at page 9 (one ADC and a multiplexer) and the description at page 11 and no parallel sample-and-hold. This could be a problem, because the conversion rate is only 7.5 Hz.The ADC is only 12 bit. The 24 bit is for watt, just a digital multiplication of the measured voltage and current. Doesn't make much sense for me, because a microcontroller could do this easily, especially at the low conversion rate.But otherwise the chip is nice. The 0.75% unadjusted error should be good for many applications and you don't need to calibrate it.

author: scientist
author_rank: Frequent Contributor
timestamp: February 05, 2014, 09:28:48 am
content: Quote from: FrankBuss on February 04, 2014, 11:23:31 pmThe Amazon Kindle displays a "charge me" screen with instructions once the battery gets below a certain level. I can imagine those watch guys included a button cell or somesuch device that has enough charge to flip the display into a similar warning screen, and just waits until it gets recharged to do anything more.

author: jwm
author_rank: Regular Contributor
timestamp: February 05, 2014, 10:36:07 am
content: Quote from: FrankBuss on February 05, 2014, 07:34:49 amerf. you are right. What's the word for when you are reading a half dozen datasheets at once and start conflating their stats? datasheetlexia?I still need to do something fun with my 2945's I was thinking of putting two in a box isolated from each other for a dual channel power meter but it would also be able to divide them to show efficiency. The idea being you can hook it up around a dc-dc converter.

author: FrankBuss
author_rank: Unknown
timestamp: April 05, 2017, 10:40:02 pm
content: Quote from: FrankBuss on February 04, 2014, 03:01:53 pmAs many of my hobby project ideas, I didn't finish it, but I dug up the display and plan to use it for another project. What is interesting to note: The test image I used was now for more than 3 years on the display and is still as good to see as on the first day, without power:Maybe the white pixels now are a tiny little bit darker.

author: amyk
author_rank: Super Contributor
timestamp: April 06, 2017, 02:34:05 am
content: That display claims to have an "external timing controller", suggesting you can control the actual drive waveforms, but upon looking at the datasheet it seems to be a SPI-ish interface with an internal timing controller.The reason the external timing controller is interesting is because you would be able to do grayscale and fast-update-tricks with that display if you had access to the raw signals: the change in contrast of each pixel is proportional to voltage * time, so by changing how long the actual "electrophorese" pulse is applied, you can control the pixel intensities. It's temperature and display-dependent so would require a little bit of calibration, but the basic principles are pretty straightforward. More info on that in this thread:https://www.eevblog.com/forum/microcontrollers/interfacing-epd-(e-ink)-display-from-kindle-anyone-tried/msg557842/

author: FrankBuss
author_rank: Unknown
timestamp: April 06, 2017, 06:12:04 pm
content: I checked the source code for the Rasperry Pi and it measures the temperature and has some delays and repetitions based on the temperature. Might be interesting trying to display gray scale images.