From 260cb31975911a75498e9ce85efd432832b4c25e Mon Sep 17 00:00:00 2001 From: Sadeep Madurange Date: Sat, 27 Dec 2025 21:54:08 +0800 Subject: Etlas. --- _site/log/etlas/index.html | 62 ++++++++++++++++++++-------------------------- 1 file changed, 27 insertions(+), 35 deletions(-) (limited to '_site/log/etlas/index.html') diff --git a/_site/log/etlas/index.html b/_site/log/etlas/index.html index e4a4a9e..678321d 100644 --- a/_site/log/etlas/index.html +++ b/_site/log/etlas/index.html @@ -44,40 +44,34 @@

ETLAS: E-PAPER DASHBOARD

05 SEPTEMBER 2024

-

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.

+

Repurposed e-reader prototype into something for regular use. +News, stocks, weather dashboard. ESP32 NodeMCU D1 + 7.5” Waveshare e-paper + +DHT22 sensor.

+ + +
front back
front
-

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.

+

Stocks: Two weeks EOD prices from Polygon.io (max SRAM holds). Flask app on VPS +relays feed, lets me swap symbols via config. FastCGI + httpd + htpasswd.

-

The following diagram outlines the Etlas’s overall system architecture.

+

gui_plot_stocks() is CPU heavy and triggers the WDT. vTaskDelay() prevents +that. Stepped graph easier to code for the bit-packed framebuffer (especially +under current memory constraints), but its messy–too messy.

-

architecture

+

Note to self: Refactor gui_plot_stocks(). Bresenham’s Line Algorithm perhaps?

-

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.

+

News: Channel NewsAsia RSS. MCU parses XML directly. Character glyphs stored as +bitmaps in sprites directory.

-

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:

+

Weather: DHT22 via PWM. 26µs/50µs/70µs pulses too fast for standard ESP32 APIs. +Compare relative pulse widths:

static inline int dht_await_pin_state(int state, int timeout)
 {
@@ -87,12 +81,12 @@ relative pulse widths to differentiate zeros from ones:

     for (t = 0; t < timeout; t += delta) {
         ets_delay_us(delta);
         if (gpio_get_level(DHT_PIN) == state)
-          return t;
+            return t;
     }
     return 0;
 }
 
-static inline int dht_get_raw_data(unsigned char buf[DHT_DATA_LEN])
+static inline int dht_get_raw_data(unsigned char buf[BUFLEN])
 {
     int rc;
     unsigned char i, pwl, pwh;
@@ -117,7 +111,7 @@ static inline int dht_get_raw_data(unsigned char buf[DHT_DATA_LEN])
         return 0;
     }
 
-    for (i = 0; i < DHT_DATA_LEN; i++) {
+    for (i = 0; i < BUFLEN; i++) {
         if (!(pwl = dht_await_pin_state(1, 50))) {
             rc = 4;
             xQueueSend(dht_evt_queue, &rc, (TickType_t) 0);
@@ -134,19 +128,17 @@ static inline int dht_get_raw_data(unsigned char buf[DHT_DATA_LEN])
 }
-

I ported this implementation from ESP8266 -to ESP32—all credit for the algorithm belongs to them.

+

Ported from ESP8266.

-

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.

+

After flashing new versions, display would stop responding. Didn’t observe this +with e-reader. Issue occurs spontaneously. Couldn’t find root cause. Making a +change like adding a comment or tweaking delay in refresh() (then changing +back) fixed it. Noisy electrical connections?

-

Etlas has been running reliably for over a year since August 2024.

+

Once running, it runs: August 2024 - December 2025.

-

Files: source.tar.gz

+

Commit: +a92c86a

by W. D. Sadeep Madurange

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