EPD (e-paper display) technology is successfully used for a long time only in typically consumer solutions, such as ebook readers. But thanks to the constant development, e-paper also started to appear more often in transport applications and digital signage.
Unisystem has been offering e-paper products for several years. Thanks to the technological partnership with E Ink – the originator, pioneer and a global leader of this technology, the company`s offer is constantly developing. After the launching of open-frame modules (which significantly simplify the implementation of delicate EPD displays in end devices), it is the time to present a solution related to controlling the displayed information.
EPD controllers by Unisystem
The RnD team from Unisystem developed three controllers that support the most popular sizes of e-paper displays used in industrial applications. The first one supports displays from 7.8’’ up to 11.3’’, and including the medium sized 9.7’’ displays. The second controller is dedicated to e-papers with diagonal of 13.3’’ – both BW (black & white version) and BWR (black, white & red). The last handles one of the largest e-paper – 31.2’’ display.
One of the most important issues during the design work was the ease of integration and implementation of a complete solution in the end product and significant facilitation of the complex image control. The controller is powered from a single source (5V) and enables communication via SPI and USB interfaces. It supports 4-bit graphics (16 level grayscale), which increases the possibilities of using e-paper displays in digital signage applications.
Image refresh modes
EPD technology works best for static applications with interactive elements. The biggest problem was the low refresh rate of the shown image. Currently, we can display information using various modes that differ not only in frequency but also in the accuracy of the mapping. Thanks to such a solution, reducing the precision of the projection will allow us to obtain a much smoother image. The Unisystem controller supports both partial changes of the displayed image and flashless mode, which makes it a flexible solution adapting to the needs of the final application.
The Initialize mode is one of the waveforms that make the global change of the displayed image. It is used when the display remains in an unknown state, i.e. if the previous image was lost during the restart. The Direct Update waveform starts the flashless mode in which the displayed image is changed. In this case, each of the pixels in the 16 level grayscale can be converted only to black or white pixel. The refresh time is 260 ms at 25°C.
GC16 mode (Grayscale Clear) can be used while changing the images in the 16 level grayscale. Each pixel can be updated or cleared. This mode is referred to as “flashy”. There is also a similar GCC16 option, which is even more flashy and is also used for 4-bit graphics. In this mode, we can receive the best image quality. Both described above modes are used for a global change of the displayed content and are referred to as “medium flashy”. The main difference between these waveforms is refreshing times – 980ms for GC16 and 1240 ms for GCC16.
GL16 is a flashless mode that should only be used with a full update of the displayed content. It works globally using a 16 level grayscale. It is ideally suited for updating anti-aliased texts. The refreshing time is 980 ms in standard conditions.
|Mode||Global / Local||Grayscale mapping||Ghosting||Refresh time [ms]||Usage|
|DU||Local||4-bit to 1-bit||Low||260||Monochromatic 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 scroll at low contrast|
|DU4||Local||4-bit to 2-bit||Medium||290||Antialiased text on touch menu|
Animation on e-paper?
The next two modes can be described as interactive. The Animation is a flashless mode that can be used for frequent and rapid content changes as well as simple animations. Image quality and ghosting have been reduced and the response time is faster – 120ms at 25°C. Remember that currently, the Animation mode will work with black & white graphics only.
Grayscale transitions are supported by DU4 mode, which is also flashless and resembles the Direct Update described above. In this waveform, each pixel in the 16-level grayscale is will be changed to a pixel in 4-level grayscale (0 – black, 5, 10, 15 – white). Thanks to the combination of fast reaction time and keeping the grayscale it works well in anti-aliased texts, like in the restaurant menus.
EPD in the outdoor version
Thanks to the development of technology, the use of e-paper displays outside of the buildings have become a reality. At low temperatures, the density of the fluid in which the e-capsules are immersed increases. This may cause problems with a refreshing and changing the displayed content. Engineers from Unisystem have prepared a solution thanks to which e-paper displays can work efficiently at -20°C.
Complete e-paper solutions
Unisystem, offering single displays (USE series), as well as an assembled display with controller (USEC series) and complete modules (USEM line), provides a comprehensive solution and support in the integration of EPD with the end device. E-paper solutions are becoming more and more common in public space in the form of, i.e. timetables, price labels, transport labels, and even architectural elements.
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