For a long time, EPD technology was used only in typical consumer solutions, such as e-book readers. Thanks to continued development, e-paper has also begun to appear more and more in transportation or digital signage applications.
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Unisystem has been offering e-paper products for several years now. Thanks to its technology partnership with E Ink – the originator, pioneer and world leader of this technology – the company’s offerings continue to grow. Following the launch of open-frame modules that significantly simplify the implementation of sensitive EPD displays in end devices, it’s time to present a solution related to display control.
EPD controllers from Unisystem
Unisystem’s RnD division has prepared three controllers that support the most popular sizes of e-paper displays that appear in industrial applications. The first one supports displays from 7.8” via 9.7” all the way up to 11.3” . The second controller is dedicated to 13.3” displays – both in the version BW (black and white) , as well as BWR (black-white-red) . The latest supports one of the largest e-paper displays, the 31.2” .
During the design work, one of the most important issues was the ease of integration and implementation of the complete solution in the finished product, as well as significant facilitation of the complex image control on the e-paper display. The controller is powered by a single 5V source and allows communication via SPI and USB interfaces. It supports 4-bit graphics (16-degree grayscale), which enhances the use of e-paper displays in digital signage applications.
Refresh modes
EPD technology works best for static applications with interactive elements. The biggest problem was the low frame rate. We can now display information in various modes that differ not only in frequency, but also in mapping accuracy. With this solution, the reduction in mapping precision will allow us to get a much smoother image. The Unisystem controller supports both partial change of displayed image and flashless mode, making it a flexible solution that adapts to the needs of displayed images.
Initialize mode is one of the waveforms that change the content across the display. It is used when the display remains in an unknown state, such as if the previous image was lost during a restart. Waveform Direct Update starts flashless mode in which the displayed image is changed. In this case, each pixel in the 16-degree grayscale can only be converted to a black or white pixel. The refresh time is 260ms at an ambient temperature of 25°C.
Grayscale Clear (GC16) is the mode used when the image is altered in 16-degree grayscale. Each pixel can be updated or cleared. This mode is referred to as “flashy” or flickering. There is also the GCC16(Greyscale Clear, 16 levels) mode, which is even shinier than GC16 and is also used for 4-bit grayscale images. In this mode, we are guaranteed to get the best image quality. Both are used in the overall change of displayed content and are referred to as “medium flash,” meaning with reduced flicker. Response times are 980ms for the GC16 and 1240ms for the GCC16, respectively.
Waveform GL16 is a flashless mode that should only be used with a full update of the displayed content. It works globally using a 16-degree gray scale. It is ideal for updating content with anti-aliasing. The response time is 980 ms under standard conditions.
| Mode | Global / Local | Graphic mode | Ghosting | Refresh time [ms] | Example application |
|---|---|---|---|---|---|
| INIT | Global | n/a | n/a | 2000 | Display initialization |
| DU | Local | 4-bit to 1-bit | Low | 260 | Monochrome menu, text input |
| GC16 | Global | 4-bit | Very low | 480 | High quality images |
| GL16 | Global | 4-bit | Medium | 480 | Text on white background |
| A2 | Local | 1-bit | Medium | 120 | Fast page scrolling at low contrast |
| DU4 | Local | 4-bit to 2-bit | Medium | 290 | Anti-alias text in menus on touch screens |
Animation on e-paper?
The next two modes can be described as interactive. Mode Animation is a flashless mode that can be used for frequent and fast content changes, as well as simple animations. Image quality and ghosting have been reduced, and response times are faster – 120 ms at 25°C. It is worth noting that currently Animation mode can only be used with black&white graphics.
Grayscale transitions are supported by DU4 mode, which is also flashless and somewhat resembles Direct Update, described above. In this case, each pixel in the 16-degree gray scale is changed to a pixel in the 4-degree gray scale (0-black, 5, 10, 15-white). This combination of fast response time and grayscale preservation works well for anti-aliased text on restaurant menus, for example.
EPD outdoors
Thanks to advances in technology, the use of e-paper displays outdoors has become a reality. At low temperatures, the density of the liquid in which the e-capsules are immersed increases. This can cause problems with refreshing and changing the displayed content. Engineers from Unisystem have prepared a solution thanks to which e-paper displays can operate efficiently even at -20°C.
Complete e-paper solutions
Unisystem offering both single displays ( USE series ), as well as sets composed of a display and controller ( USEC series ) and complete modules ( USEM series ), provides a comprehensive solution and support for the targeted integration of e-paper displays into the end device. Solutions using e-paper are becoming increasingly common in public spaces in the form of, for example, timetables, price tags in stores, transportation labels, and even as architectural elements.
If you need more information – contact us.