From e15f1076b59e997108914f6a5b9b28652d323268 Mon Sep 17 00:00:00 2001 From: Sadeep Madurange Date: Sat, 20 Dec 2025 21:36:45 +0800 Subject: Change website structure to a log. --- _poc/etlas.md | 114 ---------------------------------------------------------- 1 file changed, 114 deletions(-) delete mode 100644 _poc/etlas.md (limited to '_poc/etlas.md') diff --git a/_poc/etlas.md b/_poc/etlas.md deleted file mode 100644 index 5eb0d25..0000000 --- a/_poc/etlas.md +++ /dev/null @@ -1,114 +0,0 @@ ---- -title: "Etlas: e-paper dashboard" -date: 2024-09-05 -thumbnail: thumb_sm.jpg -layout: post ---- - -Etlas is a news, stock market, and weather tracker powered by an ESP32 NodeMCU -D1, featuring a 7.5-inch Waveshare e-paper display and a -DHT22 sensor module. - - - - - - -
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- -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. - -The following diagram outlines the Etlas's overall system architecture. - -![architecture](etlas_arch.png) - -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. - -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: - -``` -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; -} -``` - -I ported this implementation from ESP8266 -to ESP32—all credit for the algorithm belongs to them. - -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 -examples for Arduino and STM32 -platforms. - -Etlas has been running reliably for over a year since August 2024. - -Files: [source.tar.gz](source.tar.gz) -- cgit v1.2.3