E-ink on the KindleIn this part of the series on E-book readers, I’ll take a peek behind the screen and try and show what makes an E-book reader tick. I’ll also look at the common specifications that most e-book readers have. I’ll be concentrating on E-ink based e-book readers, because these seem to be the most dominant form of e-book reader devices today.

The Screen

Most E-book readers today use an e-ink display screen. Sounds really high tech right? Well, it is. I’ll try and explain how e-ink works.

An e-ink display basically consists of material called “electronic ink” which is printed onto a thin sheet of plastic. “Electronic ink” or e-ink consists of millions of micro capsules which have colored chips that may be black or white in color. Each color responds to electricity in a different manner. Let’s assume that the white chips respond to a positive charge and the black chips respond to a negative charge. Now when an positive charge is applied to a micro capsule this causes the white chips to rise up to the top of the capsule, while the black chips sink to the bottom. This makes the capsule appear white. When a negative charge is applied, the capsule appears black through a similar process.
Now if you imagine that each capsule represents a pixel, you can easily see how a black and white image may be created by the selective application of charge to each micro capsule. This is the essence of the e-ink display.
The advantage of using this kind of display is that it consumes no power to maintain display of the image, and only consumes power when changing the text or image on screen, say during a page turn.  In addition to this the text renders with extremely good contrast, which allows for reading in direct sunlight with minimal eye strain, just like the dead-tree book.

Drawbacks of E-ink Screens

A minor side effect is that the screen gives a nasty “flash” when changing pages. Also e-ink displays suffer from very low refresh rates, making the use of interactive applications difficult. So far the technology used for making e-ink displays has only been able to generate grayscale screens for the commercial market (though color screens should be ready for the market in a year or so).  As most of the fiction and non-fiction books on the market do not feature color illustrations, I don’t think this really should be a problem. However lack of color does pose problems if the e-ink screen is to be used to read books where color illustrations are important.

Rivals of the e-ink Screen

Rival screen technologies are centered on the old tried and tested LCD display and its variants. In addition to this, rival screen solutions like displays from Kent displays, Pixel Qi and research at Qualcomm should bring in diversity in the market in the near future. But as of today it seems the future of the e-book reader is tied to the e-ink display.

The internals

Now that I have given you a glimpse at what’s behind the screen, let’s look at the other specifications for these devices.
Most of the devices available in the market give you about 7500+ page turns worth of power. Yes, you heard me right, page turns. It seems that the e-ink screens have spawned a new metric to measure battery life called “page turns”. 7500+ page turns effectively means that you ought to get through two or three bestsellers easily before needing to re-charge the device.
Which brings us to the power source. Lithium based power sources seems to be the universal choice of the e-book readers. Most e-book readers have Lithium-ion or Lithium-polymer batteries, and these are usually proprietary, which means that there is some amount of lock-in with the manufacturer for the batteries.
The heart of the device, the processor, is usually 400-500 MHz in the newer models, while it is about 200-250 MHz in some of the older ones as well as the newer entry level models. Almost all e-book readers these days run on Linux. Most support TXT, PDF, RTF/DOC, HTML and at least one DRM format.

The interface

E-ink based readers have low refresh rates, which poses a problem while designing the user interface. Different manufacturers have got around this problem using different techniques. The most common method is to provide buttons that allow choosing a menu option directly. A popular variant of this method is to provide numbered buttons, a number corresponding to a visible menu option. Others like the Cool-er provide a four way controller that allows for a choice of menu options, and the Kindle provides a full fledged keyboard on the device. Another popular way to get around this problem is used by Sony on the PRS-700. Here they have basically overlaid a touch screen over the e-ink display which allows for navigation via touch. Lastly, the most interesting method is one used by Jinke Electronics on one of their e-book reader models. They have basically developed a smaller slave touch screen that is separate from the e-ink display and is used for interaction with the device.

Content Delivery

Most devices use an USB interface to get content on to the device. Some even have support for a LAN port and Wi-Fi access. Amazon’s Kindle provides wireless access to its online store to get content on to the device using Sprint’s network in the US.
With this look at the technology behind the e-book readers, in the next edition of this series I’ll look at how the various e-book readers on the market compare and I’ll also look at alternatives to the e-book reader.

Kindle image from awrose at Flickr.

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