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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>
</tr>
<tr style="border: none;">
<td colspan="2" style="border: none;"><img src="etlas_arch.png" alt="front" style="width: 100%" /></td>
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</table>
<p>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.</p>
<p>gui_plot_stocks() triggers WDT. vTaskDelay() prevents that. Stepped graph was
easier to code for the bit-packed framebuffer (not enough memory for much
else), but it’s messy–too messy.</p>
<p>Note to self: Refactor gui_plot_stocks(). Bresenham’s line algorithm perhaps?</p>
<p>News: Channel NewsAsia RSS. MCU parses XML directly. Character glyphs stored as
bitmaps in sprites directory.</p>
<p>Weather: DHT22 via PWM. 26µs/50µs/70µs pulses too fast for standard ESP32 APIs.
Compare relative pulse widths:</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>Ported from <a href="https://github.com/Fonger/ESP8266-RTOS-DHT" class="external" target="_blank" rel="noopener noreferrer">ESP8266</a>.</p>
<p>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?</p>
<p>Once running, it runs: August 2024 - December 2025.</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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