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diff --git a/_site/log/etlas/index.html b/_site/log/etlas/index.html new file mode 100644 index 0000000..e4a4a9e --- /dev/null +++ b/_site/log/etlas/index.html @@ -0,0 +1,166 @@ +<!DOCTYPE html> +<html> + <head> + <meta charset="utf-8"> + <title>Etlas: e-paper dashboard</title> + + <head> + <meta charset="utf-8"> + <meta name="viewport" content="width=device-width, initial-scale=1"> + <title>Etlas: e-paper dashboard</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 class="active"> + <a href="/log/" class="link-decor-none">log</a> + </li> + <li > + <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">ETLAS: E-PAPER DASHBOARD</h2> + <h6 class="center">05 SEPTEMBER 2024</h5> + <br> + <div class="twocol justify"><p>Etlas is a news, stock market, and weather tracker powered by an ESP32 NodeMCU +D1, featuring a 7.5-inch <a href="https://www.waveshare.com/" class="external" target="_blank" rel="noopener noreferrer">Waveshare</a> e-paper display and a +DHT22 sensor module.</p> + +<table style="border: none;"> + <tr style="border: none;"> + <td style="border: none;"><img src="dash.jpg" alt="front" style="width: 100%" /></td> + <td style="border: none;"><img src="pcb.jpg" alt="back" style="width: 100%" /></td> + </tr> +</table> + +<p>The top-left panel shows two weeks of end-of-day prices—the maximum the ESP32’s +SRAM can hold—from the Polygon.io API. The price feed is relayed through a +FastCGI-wrapped Flask app hosted on a VPS. This lets me configure stock symbols +in its application settings. The app cycles through them as requests come in +from the ESP32. Running the Flask app as a FastCGI process while exposing it +via httpd with htpasswd authentication keeps the server code simple and secure.</p> + +<p>The following diagram outlines the Etlas’s overall system architecture.</p> + +<p><img src="etlas_arch.png" alt="architecture" /></p> + +<p>The more prominent panel on the right of the display shows local and world news +from Channel NewsAsia. The MCU downloads and parses XML data from the RSS feed +directly before rendering it to the display. The character glyphs used are +stored as bitmaps in the sprites directory. I skipped the proxy for news to +avoid writing more server code, but in hindsight it limits the feeds Etlas can +handle. I will fix this in a future version.</p> + +<p>The middle and bottom right panels display the temperature and relative +humidity from the DHT22 sensor. The DHT22 uses pulse-width modulation to +transmit data to the host. The 26µs, 50µs, and 70µs pulses are too fast for the +ESP32 to measure reliably with standard APIs. Instead, the driver compares +relative pulse widths to differentiate zeros from ones:</p> + +<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>static inline int dht_await_pin_state(int state, int timeout) +{ + int t; + static const uint16_t delta = 1; + + for (t = 0; t < timeout; t += delta) { + ets_delay_us(delta); + if (gpio_get_level(DHT_PIN) == state) + return t; + } + return 0; +} + +static inline int dht_get_raw_data(unsigned char buf[DHT_DATA_LEN]) +{ + int rc; + unsigned char i, pwl, pwh; + + gpio_set_level(DHT_PIN, 0); + ets_delay_us(1100); + gpio_set_level(DHT_PIN, 1); + + if (!dht_await_pin_state(0, 40)) { + rc = 1; + xQueueSend(dht_evt_queue, &rc, (TickType_t) 0); + return 0; + } + if (!dht_await_pin_state(1, 80)) { + rc = 2; + xQueueSend(dht_evt_queue, &rc, (TickType_t) 0); + return 0; + } + if (!dht_await_pin_state(0, 80)) { + rc = 3; + xQueueSend(dht_evt_queue, &rc, (TickType_t) 0); + return 0; + } + + for (i = 0; i < DHT_DATA_LEN; i++) { + if (!(pwl = dht_await_pin_state(1, 50))) { + rc = 4; + xQueueSend(dht_evt_queue, &rc, (TickType_t) 0); + return 0; + } + if (!(pwh = dht_await_pin_state(0, 70))) { + rc = 5; + xQueueSend(dht_evt_queue, &rc, (TickType_t) 0); + return 0; + } + buf[i] = pwh > pwl; + } + return 1; +} +</code></pre></div></div> + +<p>I ported <a href="https://github.com/Fonger/ESP8266-RTOS-DHT" class="external" target="_blank" rel="noopener noreferrer">this</a> implementation from ESP8266 +to ESP32—all credit for the algorithm belongs to them.</p> + +<p>Etlas is a networked embedded system. All acquisition, processing, and +rendering of data are performed on the ESP32’s 160MHz microprocessor using less +than 512KB of SRAM. The embedded software that makes this possible is written +in C using ESP-IDF v5.2.1. The e-paper display driver is derived from Waveshare +<a href="https://github.com/waveshareteam/e-Paper" class="external" target="_blank" rel="noopener noreferrer">examples</a> for Arduino and STM32 +platforms.</p> + +<p>Etlas has been running reliably for over a year since August 2024.</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> |