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<!DOCTYPE html>
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<title>Etlas: e-paper dashboard</title>
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<h2 class="center" id="title">ETLAS: E-PAPER DASHBOARD</h2>
<h5 class="center">05 SEPTEMBER 2024</h5>
<br>
<div class="twocol justify"><p>Repurposed <a href="../e-reader/">e-reader prototype</a> into something for regular use.
News, stocks, weather dashboard. ESP32 NodeMCU D1 + 7.5” Waveshare e-paper +
DHT22 sensor.</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>
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<td colspan="2" style="border: none;"><img src="etlas_arch.png" alt="front" style="width: 100%" /></td>
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<p>Stocks: Two weeks EOD prices from Polygon.io (max possible). Flask app on VPS
relays feed; manages watchlist. Backend: httpd + htpasswd + FastCGI + Flask.</p>
<p>gui_plot_stocks() triggers watchdog; vTaskDelay() required. Stepped graph was
easier to implement (under memory constraints), but the logic is hideous. Note
to self: Refactor with Bresenham’s?</p>
<p>News: Channel NewsAsia RSS. MCU parses XML directly. Character glyphs stored as
bitmaps in header files.</p>
<p>Weather: DHT22 single-wire protocol. 26µs/50µs/70µs pulses are too fast for
standard ESP32 APIs. Bit-banged relative pulse widths: (Ported from <a href="https://github.com/Fonger/ESP8266-RTOS-DHT" class="external" target="_blank" rel="noopener noreferrer">ESP8266</a>):</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[BUFLEN])
{
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 < BUFLEN; 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>Ghost in the machine: epd_init() stalls intermittently on first refresh() after
flash. Toggling delay values in refresh() resolves it. If first refresh
succeeds, it remains stable. Root cause unknown–suspected power supply issues
from powering display via MCU.</p>
<p>Uptime: August 2024 - January 2026</p>
<p>Commit:
<a href="https://git.asciimx.com/etlas/commit/?id=a92c86ac1592c2137d3d1fec1668eacc2d0ca581">a92c86a</a></p>
</div>
<p class="post-author right">by W. D. Sadeep Madurange</p>
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