Hardware

eInk, what they are and how to create an electronic ink display

eInk, what they are and how to create an electronic ink display

I display eInc, based on the principle of electrophoresis, exploit charged particles of different colors dispersed in an oil placed inside a transparent container. By applying electric fields, these particles can be moved up or down to produce black, white or a “mixture” of the two colors.

The effect obtained is similar to that of active matrix LCD displays, which also use 2D arrays of TFTs (Thin-Film Transistor) and electric fields to change state. Unlike LCD screens, however, eInk displays retain their state even after the electric field is removed, reducing the energy consumption.

eInk technology, also called electronic ink, is mainly used in eReaders and some digital display devices. The goal is to simulate the look of ink on paper, providing a reading experience that is more similar to that of printed paper than that offered by traditional LCD or LED screens.

eInk display operation

Immagine tratta da “Electronic Ink, How it works” (E Ink Holdings, Inc.)

Brief history of eInk

The term eInk commonly refers to a wide range of displays based on electrophoretic display. The technology was invented and developed between 1995 and 1997 by Barrett Comiskey, JD Albert and Joseph Jacobson, at the MIT Media Lab. The trio later founded E Ink Corporationin order to bring the technology to the market.

Known today as E Ink Holdingsthe company has played and continues to play a crucial role in the development of eInk displays.

In 1999, E Ink introduced the world’s first eInk display: called Immediate, required just 0.1W to operate. In the mid-2000s it was the turn of technology Vizplex, which significantly improved the response times of eInk displays. In 2007, Amazon presents its first e-reader Kindle, which used a 6-inch monochrome eInk display manufactured by E Ink itself. A choice that has contributed enormously to the popularity of eInk displays.

In the years that followed, E Ink continued to develop new generations of faster, higher-resolution, full-color eInk displays, expanding into various products such as e-readers, tablets, watches, and digital signs.

Advantages and disadvantages of eInk displays

Compared to LCDs, i display eInk have some advantages and disadvantages. Between advantages there are low energy consumption, the possibility of being used outdoors thanks to the reflection of light, the stability of the image even after turning off, the wide viewing angle. In fact, eInk screens require energy only during the image change and not, instead, to keep it displayed. This is why devices such as eReaders can have abattery autonomy weeks or even months on a single charge.

On the other hand, eInk is characterized by lower contrast and color gamut, as well as slower response times. Many eInk screens are capable of display only gray scales instead of full colors and, obviously, they are not suitable for the multimedia sector.

Types of eInk panels available on the market

The eInk panels currently available on the market can be divided into two main categories: with integrated controller and without integrated controller. Controllerless panels require a dedicated controller or SoC with an integrated controller to operate, increasing the cost of the system but offering greater flexibility and performance. On the other hand, panels with integrated controller have a lower cost but performance e gray levels limited.

Il controller eInk performs a similar function to display controller (DC/CRTC) e al timing controller (TCON) in a traditional LCD system. It processes image data and converts it into the signals needed to drive the screen, maintaining the state of the pixels within an integrated SRAM or SDRAM memory.

Display a colori e dithering

As mentioned previously, there are not only black-white or grayscale eInk displays on the market but also color models. There are two main technologies for creating color eInk displays: you can use a color filter array (CFA) or multi-pigment inks.

The CFA solution is similar to that used in color LCD displays; there multi-pigment technology uses ink particles of different colors within a single pixel. The latter offers superior resolution and color saturation. However, the scheme is more complex to manage, highlighting slower update times.

To improve the image quality on eInk displays, which typically support only 16 levels of gray, dithering techniques can be applied. The dithering creates the illusion of intermediate tones by distributing black and white pixels in certain patterns.

Caster and its open implementation

With the name Caster This refers to a type of eInk display that uses electronic ink technology to offer energy-efficient displays that remain readable even in direct sunlight.

Designed specifically for applications that require frequent updating of display content, such as digital signs, store shelf labels, smart watches and other small wearable devices, Caster enables sufficiently rapid updating of visual content.

An open source project is published in this GitLab repository that provides a design of low latency controller FPGA based, can be integrated into different device classes.

Glider, an “open” eInk display with an emphasis on the concept of low latency

On Amazon Europe, for example, there are dozens of examples of eInk displays. The project Gliderpublished in this GitHub repository, provides all the tools for designing the hardware and firmware of an eInk to low latency.

The hardware is based on a FPGA Xilinx Spartan-6 LX16 running Caster firmware and an EPDC (Electrophoretic Display Controller) open source optimized for low latency. The system supports DVI, DisplayPort and MIPI-DSI video inputs. It can also handle a wide range of panels eInk without integrated controller, from sizes of 4.3″ up to 13.3″ or potentially even 42″.

Display eInk open source: Glider

Instead of treating the entire screen as a single one update region, Caster treats each individual pixel as an individual region, allowing instant updating of pixels as they change. Furthermore, it implements the early cancellationthat is, if a pixel changes before being completely updated, a sudden transition towards the new requested state occurs.

Caster also takes advantage of one hybrid mode which automatically switches between binary (high speed) and 16-gray (low speed) modes on a pixel-by-pixel basis. When the input image changes, the system switches to binary mode for fast updating, while when the image remains static, it is re-rendered in grayscale for better visual quality.

Anyone who would like to try their hand at a open source project innovative that addresses the challenges related to reducing latency in eInk displays, can follow the instructions given here. Glider paves the way for new and exciting applications in the eInk display segment.

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