Etlas: e-paper dashboard

ETLAS: E-PAPER DASHBOARD

05 SEPTEMBER 2024

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

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Stocks: Two weeks EOD data from Polygon.io (max possible). Flask app on VPS -manages watchlist, relays the feed. Backend: httpd + htpasswd + slowcgi + -Flask.

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gui_plot_stocks() plots a stepped graph; was easier to implement, but the code -is hideous; triggers watchdog. vTaskDelay() prevents that.

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NOTE: Refactor. Bresenham’s?

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News: Channel NewsAsia RSS. MCU does the parsing. Didn’t plan to have a backend -at the time. Now that I have one for stocks, should relay the feed for -flexibility.

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Weather: DHT22 single-wire protocol. 26µs/50µs/70µs pulses are too fast for -standard ESP32 APIs. Bit-banged relative pulse widths (ported from ESP8266):

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static inline int dht_await_pin_state(int state, int timeout)
-{
-    int t;
-    static const uint16_t delta = 1;
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-    for (t = 0; t < timeout; t += delta) {
-        ets_delay_us(delta);
-        if (gpio_get_level(DHT_PIN) == state)
-            return t;
-    }
-    return 0;
-}
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-static inline int dht_get_raw_data(unsigned char buf[BUFLEN])
-{
-    int rc;
-    unsigned char i, pwl, pwh;
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-    gpio_set_level(DHT_PIN, 0);
-    ets_delay_us(1100);
-    gpio_set_level(DHT_PIN, 1);
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-    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;
-    }
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-    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;
-}
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epd_init() stalls intermittently on first refresh() after flash. Toggling delay -values in refresh() resolves it. If the first refresh succeeds, it remains -stable. Root cause unknown–suspect noisy power supply due to powering display -via MCU.

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Uptime: August 2024 - January 2026

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Commit: -a92c86a

by W. D. Sadeep Madurange