Open Book Touch: open-source e-reader

Open Book Touch is the device I’ve been trying to build for six years: a small, beautiful, completely open source e-book reader that does one thing and does it well. There are no physical buttons on the front; the device is a single, perfectly symmetrical 4.26-inch front-lit e-paper touchscreen, one centimeter thin in its enclosure. Open Book Touch slips into a pocket and disappears until you unlock it to read.

It’s taken a while to get here, but the TL;DR is this: it’s real now. Earlier Open Books could show you a wall of plain text. This one shows your book covers in a gorgeous, deeply designed interface, reads EPUB files (finally!), and renders dozens of writing systems. There’s Wi-Fi too, but mostly for getting books on, not for living online. And the whole thing is open source, both hardware and software, so you can hack it, fork it, tear it down, and build it back up.

It’s a liberated book for the people.

Open Book Touch isn’t trying to be a tablet. Like all of the objects I design, it makes a deliberate set of tradeoffs to do its one job beautifully:

The whole point of an e-reader is the reading, so that’s where most of the work has gone. Open Book Touch reads EPUB and plain text files straight off its microSD card: drop in your books, and they show up on the shelf.

But "it shows text" is table stakes. Open Book Touch implements a real typesetting engine, alongside gorgeous fonts in multiple weights and sizes to truly up the ante:

It’s a reader you’ll actually want to read on.

Our e-paper panel packs the 480 × 800 pixels you’d normally find on a much larger 7.5-inch display into just 4.26 inches diagonal, so everything is remarkably sharp. It’s a 1-bit display at heart (crisp black on white), and it’s dense enough that even your book covers, dithered to pure black-and-white, look genuinely delightful on the home screen.

The best part, though, is the frontlight. With both warm and cool LEDs in the frontlight module, you’re not stuck with one harsh color temperature: you can warm it all the way down for reading in bed, cool it for daylight, or dial in something in between, with fully adjustable brightness. You can read all night without wrecking your night vision (or keeping your partner awake with a reading light).

E-paper is still e-paper. The screen refreshes at a readerly pace; you’re not going to play DOOM on it. The fast 1-bit mode drives everything you touch, page turns included. The richer 2-bit grayscale takes several seconds to draw, so we save it for the lock screen: your current book cover, or a photo of your own.

This whole project started with a font. Back in 2019, I stumbled across GNU Unifont: a bitmap font with a glyph for nearly every character in the Unicode standard. I wanted to build a device that could put all the languages of the world in your hand.

Open Book Touch is the realization of that idea.

Latin scripts look great today in Lucida. Cyrillic scripts like Russian and Ukrainian are supported via GNU Unifont, along with Arabic and Hebrew. Unifont also powers our Chinese and Japanese support. Complex Indic scripts don’t yet shape fully, but as an open source project, we’d welcome your pull requests!

Open Book Touch is open hardware with MIT-licensed firmware — schematics, board files, enclosure CAD, and source, all of it out in the open. But to make this real, I had to build something bigger than the firmware. Focus, a new, bespoke C++ application framework in the spirit of NeXTSTEP’s AppKit and Apple’s UIKit, comes complete with view controllers, a touch-and-gesture system, a full set of on-screen widgets, and even an on-screen keyboard.

Focus is the system I built to power Open Book, and yet it isn’t limited to Open Book. Focus is platform-agnostic by design: the screen sits behind a small, swappable driver, and the user interface supports touch and button-based input, so the same view controllers, layout, text, and interactions run whether you’re drawing to a big 480 × 800 touchscreen or a tiny monochrome LCD with a joystick.

You’ll hear more about Focus in an upcoming backer update, but for the moment, I’m stoked to announce that we’re open-sourcing Focus today. A framework like Focus is only worth something when it gets used, and I want it out in the world for folks to start to hack on. As for the rest — the board files, the enclosure CAD, and the source code itself — we plan to release all of it when we ship. The files go public as units reach the backers who funded them, so the people who made this possible get their devices before anyone can spin up a clone.

At the center is an ESP32-S3, a dual-core microcontroller with Wi-Fi and Bluetooth LE, and we’ve given it room to work:

We finally said goodbye to fragile Arduino workflows and built the firmware on ESP-IDF and FreeRTOS, with SQLite quietly managing your library’s metadata under the hood. When your Open Book is on the same Wi-Fi network, you can send books to it from a web browser, no cables required.

And of course, you can still write code for it using Arduino or CircuitPython if you’d rather treat it as an absurdly nice e-paper dev board; it’s been tested with both.

And because so much of the hard-won wisdom from Sensor Watch went into this, it’s frugal with power: the ESP32-S3’s low-power RISC-V coprocessor sits and watches for your touch while the main chip sleeps, and when the device is locked, only the ultra-low-power real-time-clock continues to tick. In our testing, you can expect about a week of reading with the frontlight off, and well over a month of standby. Still, of course, the more you crank the frontlight, the more you’ll be reaching for that USB-C cable.

We’re committing to an 800 mAh battery as our floor, but because the case has room for the 1200 mAh cell we’ve been testing, we’ll ship the largest one we can reliably source. If we can manage that, reading time goes well past that one-week baseline.

Open Book Touch is yours in a way most devices aren’t. The battery is one you can swap yourself. The library is one you load yourself. Nothing phones home, and nobody can reach in to delete a book you own. The device answers to you, and no one else.

That goes for how it looks and feels, too. The case we’re planning to ship (and the one shown on this page) is 3D-printed: slim, lightweight, and engineered to tight tolerances. If the campaign draws enough interest, moving to an injection-molded enclosure is a stretch goal — a real step up in fit and finish — but the 3D-printed shell is what we’re committing to today.

Here’s the part I’m most excited about though: that case? It’s snap fit, which means it’s easy to take apart and put back together. And because it was designed to be 3D-printed to begin with, the files to make your own ship right alongside the rest of our CAD. Want one in brown like a leather-bound book? Sparkly pink? Translucent purple, like the old Game Boy Color? Go for it! I want Open Book Touch to look like your book, not mine.

For the folks who’d rather buy nice than print their own, we’re also offering a special edition: the same Open Book Touch, dressed up in premium materials and finish, inspired by Bunnie’s "omakase" Precursor. The exact form and materials are still taking shape, but I think it’s going to be something really special that you’re not going to want to miss.

| Open Book Touch | Xteink X4 | Kindle | Kobo Clara BW | Boox Go 6 | | |---|---|---|---|---|---| Display size | 4.26" | 4.3" | 6" | 6" | 6" | Resolution | ~220 ppi | ~220 ppi | 300 ppi | 300 ppi | 300 ppi | Touchscreen | Yes | No | Yes | Yes | Yes | DRM | None | None | Yes | Yes | Varies | Book formats | EPUB, TXT | EPUB, TXT | Kindle formats | EPUB, PDF, MOBI, TXT, HTML, RTF, CBZ, CBR, KEPUB | EPUB, PDF, MOBI, TXT, HTML, RTF, CBZ, CBR, AZW3, DJVU, DOC, DOCX | Frontlight | Warm + cool | No | Cool only | Warm + cool | Warm + cool | User-replaceable battery | Yes | No | No | Yes | No |