e ink project  - Page 1
Forum section: electronics / projects

author: Add_man
author_rank: Newbie
timestamp: October 20, 2015, 03:57:45 am
content: I want to use aE-ink segmented displaysfor a project. According to the datasheet, I can run the display at 5v or 15v. Now, the datasheet also states I drive the display directly using my MCU, which is the msp430 if I stay under 5v (page 8 in datasheet). but I haven't exactly figure out the best way/ how to, do that without the necessary number of pins?characteristics / limitations of the project:Battery Powered - low poweredSomeone what rugged - Need to withstand some dropping 5ft-10ft ( will be in a case)Compact - I'm aiming to have a total final dimensions (including case) around 30mm x 30mm ±5mm although these dimensions are not totally set.Any help and or insight would be appreciated.

author: amyk
author_rank: Super Contributor
timestamp: October 20, 2015, 04:19:04 am
content: The datasheet doesn't say much, although I suppose they expect you to figure out that all you need to do is apply +/- 5V across the back electrode and one of the segments to flip its state. You can use one MCU pin to drive the back electrode with 5V or ground, and either (a) as many pins as you have segments, or (b) a SIPO shift register to drive as many segments as shift register outputs. The display changes state depending on thedifferencein voltage between the common and segment, and the state change is dependent on the polarity. The duration of applied voltage can be used to vary the intensity of the change (e.g. starting with pure white, a short pulse will darken a pixel less than a long pulse) so you can do grayscale too. The speed of the darkening/lightening also varies depending on the applied voltage.Basically, this:Code:Common Segment Effect0V 0V no change0V 5V dark5V 0V light5V 5V no changeYou can also get dedicated driver ICs that will do this for you. More discussion on that here:https://www.eevblog.com/forum/microcontrollers/interfacing-epd-(e-ink)-display-from-kindle-anyone-tried/

author: Pjotr
author_rank: Frequent Contributor
timestamp: October 20, 2015, 12:24:21 pm
content: You can drive them between 5V and 15V. 5V directly from a micro controller. However with more voltage you'll get higher contrast but you need dedicated drivers. Maybe simple TTL --> CMOS converters will do also.

author: amyk
author_rank: Super Contributor
timestamp: October 21, 2015, 02:31:34 am
content: Perhaps some of the high-voltage shift registers used for driving multiplexed graphic LED displays would also be suitable.

author: Gall
author_rank: Frequent Contributor
timestamp: October 22, 2015, 08:30:38 am
content: Almost any 40xx series IC will do the trick.

author: Add_man
author_rank: Newbie
timestamp: October 25, 2015, 03:49:37 am
content: update:ok, so thank you for the answers, I understand the screen better now. now, I've done so digging and came up a few Solutions please feel free to correct me if I'm wrong or misunderstanding something:use a simple I/O expander. I never used one before although it seems simple but can't find a single IC expander that has 34 pins so I'll have to use 2 with possible unused pins. look inefficient.Use a serial to Parallel shift register. I have used theses, even study with them for school. but I forsee similar drawbacks as before, few single 34 output IC, although they actually exist this time. if I go with multiple ICs it gets messy quick, plus none of the compatible chips I've found run at the low power.use a cPLD as a shift register or/ I/O expander. I never use cPLD in a project nor have I ever program one. but if fixes the efficiency, multiple chips and clutter problems and I think I can even get ones for low power( I think). but there rather complex for just this and I don't know what it take to program them.please give me you opinions on this am I missing something or looking at this wrong.

author: mariush
author_rank: Super Contributor
timestamp: October 25, 2015, 04:46:45 am
content: Don't forget that the eink display will work with 5v but it will be very slow, according to their datasheets you have :5v , 60-80% contrast, refresh between 720ms and 1200ms15v , 100% contrast, refresh at about 240 ms.So as you can see, if you power it directly from 5v, the update rate will be horrible, an average of one update a second.It would make sense to aim for the 15v, but I think the eink display will also work with other intermediary voltages or some voltage close to 15v. I would think 12v would be a safe choice, and should still guarantee an update every 300ms or so.If you go this route, obviously you'd need to somehow send 15v to each segment and turn on / off each segment... which would be difficult since we're talking about two different voltages.Unless I'm really wrong (because i haven't slept all night) , you can use npn darlington array ICs likeULN2803between the microcontroller or basic shift register and the segments. The 8 inputs (the bases of each transistor in the array) take 5v from mcu/shift register and you feed 15v or whatever higher voltage you want on the common pin. Sure, it will take a lot of pcb space... and that's why actual eink drivers exist.

author: Pjotr
author_rank: Frequent Contributor
timestamp: October 25, 2015, 07:20:10 am
content: The segments of these displays are simply small capacitors electrically. Cmos level shifters will do the trick to drive them with 15V. But you need a lot because you'll need to drive each segmentandthe back separately. Basically they work similar like bi-stable relays with one coil, instead of current you drive them with voltage of the right polarity to set/reset them.

author: Gyro
author_rank: Super Contributor
timestamp: October 25, 2015, 09:42:32 am
content: The shift register approach looks the best to me, using CD4094 shift registers running at 15V. Then you only have to level shift 3 signals (just one transistor and two resistors per signal).

author: Add_man
author_rank: Newbie
timestamp: October 28, 2015, 08:23:24 am
content: found this article in the course of my research though it was interestinghttp://hackaday.com/2008/10/14/how-to-make-an-e-paper-clock-and-hack-esquire-magazine/