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diff --git a/_site/poc/e-reader/index.html b/_site/poc/e-reader/index.html new file mode 100644 index 0000000..6f52897 --- /dev/null +++ b/_site/poc/e-reader/index.html @@ -0,0 +1,148 @@ +<!DOCTYPE html> +<html> + <head> + <meta charset="utf-8"> + <title>Experimental e-reader</title> + + <head> + <meta charset="utf-8"> + <meta name="viewport" content="width=device-width, initial-scale=1"> + <title>Experimental e-reader</title> + <link rel="stylesheet" href="/assets/css/main.css"> + <link rel="stylesheet" href="/assets/css/skeleton.css"> +</head> + + + + </head> + <body> + + <div id="nav-container" class="container"> + <ul id="navlist" class="left"> + + <li > + <a href="/" class="link-decor-none">hme</a> + </li> + <li > + <a href="/log/" class="link-decor-none">log</a> + </li> + <li class="active"> + <a href="/poc/" class="link-decor-none">poc</a> + </li> + <li > + <a href="/about/" class="link-decor-none">abt</a> + </li> + <li><a href="/feed.xml" class="link-decor-none">rss</a></li> + </ul> +</div> + + + + <main> + <div class="container"> + <div class="container-2"> + <h2 class="center" id="title">EXPERIMENTAL E-READER</h2> + <h6 class="center">24 OCTOBER 2023</h5> + <br> + <div class="twocol justify"><p>This project features an experimental e-reader powered by an ESP-WROOM-32 +development board and a 7.5-inch <a href="https://www.waveshare.com/" class="external" target="_blank" rel="noopener noreferrer">Waveshare</a> +e-paper display built with the intention of learning about e-paper displays.</p> + +<video style="max-width:100%;" controls="" poster="poster.png"> + <source src="ereader.mp4" type="video/mp4" /> +</video> + +<h2 id="introduction">Introduction</h2> + +<p>The prototype e-reader comprises an ESP32 microcontroller, an e-paper display +HAT, and three buttons: yellow, blue, and white for turning the page backwards, +forwards, and putting the device to sleep, respectively. The prototype does not +store books on the microcontroller. It streams books from a server over HTTP. +The e-reader employs RTC memory to record the reading progress between +sessions.</p> + +<p>The most formidable challenge when trying to build an e-reader with an ESP32 is +its limited memory and storage. My ESP-WROOM-32 has a total of 512KB of SRAM +and 4MB of flash memory, which the freeRTOS, ESP-IDF, and the e-reader +application must share. To put things into perspective, a Kindle Paperwhite has +at least 256MB of memory and 8GB of storage. That is 500x more memory than what +I’d have to work with.</p> + +<p>Despite its size, as microcontrollers go, ESP32 is a powerful system-on-a-chip +with a 160MHz dual-core processor and integrated WiFi. So, I thought it’d be +amusing to embrace the constraints and build my e-reader using a $5 MCU and the +power of C programming.</p> + +<h2 id="the-file-format">The file format</h2> + +<p>The file format dictates the complexity of the embedded software. So, I’ll +begin there. The e-reader works by downloading and rendering a rasterized +monochrome image of a page (a .ebm file).</p> + +<p>The EBM file contains a series of bitmaps, one for each page of the book. The +dimensions of each bitmap are equal to the size of the display. Each byte of +the bitmap encodes information for rendering eight pixels. For my display, +which has a resolution of 480x800, the bitmaps are laid out along 48KB +boundaries. This simple file format lends well to HTTP streaming, which is its +main advantage, as we will soon see.</p> + +<p>The pdftoebm.py script enclosed in the tarball at the end of the page converts +PDF documents to EBM files.</p> + +<h2 id="how-does-it-work">How does it work?</h2> + +<p>As the e-reader has no storage, it can’t store books locally. Instead, it +downloads pages of the EBM file over HTTP from the location pointed to by the +<code class="language-plaintext highlighter-rouge">EBM_ARCH_URL</code> setting in the Kconfig.projbuild file on demand. To read a +different book, we have to replace the old file with the new one or change the +<code class="language-plaintext highlighter-rouge">EBM_ARCH_URL</code> value. The latter requires us to recompile the embedded +software.</p> + +<p>Upon powering up, the e-reader checks the reading progress stored in the RTC +memory. It then downloads three pages (current, previous, and next) to a +circular buffer in DMA-capable memory. When the user turns a page by pressing a +button, one of the microprocessor’s two cores transfers it from the buffer to +the display over a Serial Peripheral Interface (SPI). The other downloads a new +page in the background. I used the ESP-IDF task API to schedule the two tasks +on different cores of the multicore processor to make the reader more +responsive.</p> + +<p>I designed the EBM format with HTTP streaming in mind. Since the pages are laid +out in the EBM file along predictable boundaries, the e-reader can request +pages by specifying the offset and the chunk size in the HTTP Range header. Any +web server will process this request without custom logic.</p> + +<h2 id="epilogue">Epilogue</h2> + +<p>My fascination with e-paper began back in 2017, when I was tasked with +installing a few displays in a car park. Having no idea how they worked, I +remember watching the languid screens refresh like a Muggle witnessing magic. +This project was born out of that enduring curiosity and love of e-paper +technology.</p> + +<p>Why did I go to the trouble of building a rudimentary e-reader when I could +easily buy a more capable commercial e-reader? First of all, it’s to prove to +myself that I can. More importantly, there’s a quiet satisfaction to reading on +hardware you built yourself. You are no longer the powerless observer watching +the magic happen from the sidelines. You become the wizard who makes the +invisible particles swirl into form by whispering C to them. There’s only one +way to experience that.</p> + +<p>Files: <a href="source.tar.gz">source.tar.gz</a></p> +</div> + <p class="post-author right">by W. D. Sadeep Madurange</p> + </div> + </div> + </main> + + <div class="footer"> + <div class="container"> + <div class="twelve columns right container-2"> + <p id="footer-text">© ASCIIMX - 2025</p> + </div> + </div> +</div> + + + </body> +</html> |