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diff --git a/_projects/e-reader.md b/_projects/e-reader.md index cefbb03..9598e46 100644 --- a/_projects/e-reader.md +++ b/_projects/e-reader.md @@ -5,34 +5,30 @@ thumbnail: thumb.png layout: post --- -This project features a minimal 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. +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. <video style="max-width:100%;" controls="" poster="thumb.png"> <source src="ereader.mp4" type="video/mp4"> </video> -## Overview +## Introduction -In 2017, I was tasked with installing some e-paper displays in a car park. Not -knowing how they worked, I remember marveling at their sight like a Muggle -witnessing magic. As someone who enjoys reading, I found e-paper to be a true -innovation. This project was born out of that enduring curiosity and love of -e-paper technology. +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. -The prototype, while far from ready for daily use, has some nifty features that -fellow hobbyists and tinkerers may find interesting. The reader can display -books of arbitrary sizes by streaming them over HTTP. It employs sleep modes to -minimize power consumption when not in use and records the reading progress in -the chip's RTC memory. - -The most formidable challenge when trying to build an e-reader with an ESP32 -board is its limited memory and storage. My ESP-WROOM-32 board has 512KB of -SRAM and 4MB of flash memory, which the freeRTOS, ESP-IDF, and the e-reader +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. +at least 256MB of memory and 8GB of storage. That is 500x more memory than what +I'd have to work with. 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 @@ -69,26 +65,29 @@ 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's task API to distribute the two -tasks between the available cores to make the reader more responsive. +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. 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. -## Reflections - -It's been six years since the car park and the displays. I began this project -hoping to learn more about e-paper displays, and I got that and more. By -working within the constraints of the ESP32, I forced myself to explore some of -its advanced features: sleep modes, multicore task scheduling, DMA transfers, -and RTC memory. - -As for the prototype, while it's no match for a commercial e-reader with -features like an offline library of books and touch screens, there's something -to be said about reading on hardware you built yourself. You are no longer the -powerless Muggle watching others perform magic. You are the wizard who makes -the invisible particles swirl into form by whispering C to them. +## Epilogue + +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. + +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. Files: [source.tar.gz](source.tar.gz) |