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| author | Sadeep Madurange <sadeep@asciimx.com> | 2025-12-20 11:25:26 +0800 |
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| committer | Sadeep Madurange <sadeep@asciimx.com> | 2025-12-20 11:25:26 +0800 |
| commit | 8cbe75f0047732c865f58e2f847a5ffafe066e71 (patch) | |
| tree | acd75f1a370bbdcc83db4cdaab481fb700c78db9 /_site/projects/e-reader/index.html | |
| parent | 9ac8970b08550a83e9ba686d0e9357654373a047 (diff) | |
| download | www-8cbe75f0047732c865f58e2f847a5ffafe066e71.tar.gz | |
Change projects to poc and blog to log.
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diff --git a/_site/projects/e-reader/index.html b/_site/projects/e-reader/index.html deleted file mode 100644 index fb48a9d..0000000 --- a/_site/projects/e-reader/index.html +++ /dev/null @@ -1,148 +0,0 @@ -<!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="/blog/" class="link-decor-none">blg</a> - </li> - <li class="active"> - <a href="/projects/" 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> |