feat(examples): add Bitcoin block clock (mempool.space, block height + fees + halving)

README.md

@@ -209,7 +209,8 @@ esp32project/
     ├── 01_hello_display.cpp
     ├── 02_blink_rgb_led.cpp
     ├── 03_button_input.cpp
-    └── 04_wifi_scan_serial.cpp
+    ├── 04_wifi_scan_serial.cpp
+    └── 05_bitcoin_block_clock.cpp
 ```
 
 `src/main.cpp` is deliberately written **without a GUI framework** (no
@@ -229,6 +230,9 @@ If you're new to ESP32 development, try the examples in this order:
 2. `02_blink_rgb_led.cpp` — control the onboard RGB LED.
 3. `03_button_input.cpp` — read input from the physical BOOT button.
 4. `04_wifi_scan_serial.cpp` — scan nearby Wi-Fi networks and print the results to the Serial Monitor.
+5. `05_bitcoin_block_clock.cpp` — connect to mempool.space over HTTPS and
+   display the current block height, next halving countdown, and fee rates.
+   A working starting point for any Bitcoin-aware device app.
 
 To try an example, copy its contents into `src/main.cpp`, build the project, and upload it to the board.
 
@@ -257,8 +261,8 @@ it:
 - Add [LVGL](https://lvgl.io/) for real widgets (buttons, sliders, menus)
   instead of hand-drawn text screens.
 - Use the microSD slot to log IMU data or load images/fonts.
-- Add BLE (the ESP32-S3 supports it alongside Wi-Fi) for a phone-controlled
-  interface.
+- Extend `05_bitcoin_block_clock.cpp` with price data, a Lightning invoice
+  QR code (see the `qrcode` library for ESP32), or BLE push to a companion phone app.
 - Wire up a 3.7V Li-Po battery to the JST connector and add deep-sleep
   power management for a portable build.
 

examples/05_bitcoin_block_clock.cpp

@@ -0,0 +1,234 @@
+// Example: Bitcoin block clock.
+// Polls the public mempool.space API every 60 s over Wi-Fi and draws:
+//   - Current block height
+//   - Blocks remaining until the next halving + a rough day estimate
+//   - Recommended fee rates (fast / half-hour / hour, in sat/vB)
+//
+// Same Wi-Fi connect flow, but now fetching live data over HTTPS and rendering it instead of just
+// printing to Serial. No API key needed.
+
+#include <Arduino.h>
+#include <WiFi.h>
+#include <WiFiClientSecure.h>
+#include <HTTPClient.h>
+#include <ArduinoJson.h>
+
+#define LGFX_USE_V1
+#include <LovyanGFX.hpp>
+
+#include "pins_config.h"
+
+#define WIFI_SSID "your_ssid"
+#define WIFI_PASS "your_password"
+
+// How often to re-poll the API.
+static const unsigned long POLL_INTERVAL_MS = 60UL * 1000UL;
+
+class LGFX : public lgfx::LGFX_Device {
+  lgfx::Panel_ST7789 _panel_instance;
+  lgfx::Bus_SPI _bus_instance;
+  lgfx::Light_PWM _light_instance;
+
+ public:
+  LGFX(void) {
+    {
+      auto cfg = _bus_instance.config();
+      cfg.spi_host = SPI2_HOST;
+      cfg.spi_mode = 0;
+      cfg.freq_write = 40000000;
+      cfg.spi_3wire = true;
+      cfg.pin_sclk = PIN_LCD_SCLK;
+      cfg.pin_mosi = PIN_LCD_MOSI;
+      cfg.pin_miso = -1;
+      cfg.pin_dc = PIN_LCD_DC;
+      _bus_instance.config(cfg);
+      _panel_instance.setBus(&_bus_instance);
+    }
+    {
+      auto cfg = _panel_instance.config();
+      cfg.pin_cs = PIN_LCD_CS;
+      cfg.pin_rst = PIN_LCD_RST;
+      cfg.panel_width = LCD_WIDTH;
+      cfg.panel_height = LCD_HEIGHT;
+      cfg.offset_x = LCD_COL_OFFSET;
+      cfg.offset_y = LCD_ROW_OFFSET;
+      cfg.invert = true;
+      _panel_instance.config(cfg);
+    }
+    {
+      auto cfg = _light_instance.config();
+      cfg.pin_bl = PIN_LCD_BL;
+      _light_instance.config(cfg);
+      _panel_instance.setLight(&_light_instance);
+    }
+    setPanel(&_panel_instance);
+  }
+};
+
+static LGFX lcd;
+
+static uint32_t blockHeight = 0;
+static uint32_t feeFast = 0;
+static uint32_t feeHalfHour = 0;
+static uint32_t feeHour = 0;
+static bool dataValid = false;
+static String lastError;
+
+// Bitcoin halves its block subsidy every 210,000 blocks.
+static uint32_t nextHalvingBlock(uint32_t height) {
+  return ((height / 210000) + 1) * 210000;
+}
+
+// mempool.space serves plain HTTPS with a standard public CA cert, this is essentially a demo
+static bool httpGet(const char *url, String &body) {
+  WiFiClientSecure client;
+  client.setInsecure();
+
+  HTTPClient http;
+  http.begin(client, url);
+  http.setTimeout(8000);
+  int code = http.GET();
+  bool ok = (code == 200);
+  body = ok ? http.getString() : "";
+  http.end();
+  return ok;
+}
+
+static bool refreshChainData() {
+  String body;
+
+  if (!httpGet("https://mempool.space/api/blocks/tip/height", body)) {
+    lastError = "height request failed";
+    return false;
+  }
+  blockHeight = (uint32_t)body.toInt();
+
+  if (!httpGet("https://mempool.space/api/v1/fees/recommended", body)) {
+    lastError = "fees request failed";
+    return false;
+  }
+  JsonDocument doc;
+  if (deserializeJson(doc, body)) {
+    lastError = "fee JSON parse error";
+    return false;
+  }
+  feeFast = doc["fastestFee"] | 0;
+  feeHalfHour = doc["halfHourFee"] | 0;
+  feeHour = doc["hourFee"] | 0;
+
+  dataValid = true;
+  lastError = "";
+  return true;
+}
+
+// Drawing
+static void drawHeader(const char *title) {
+  lcd.fillScreen(TFT_BLACK);
+  lcd.setTextColor(TFT_ORANGE, TFT_BLACK);
+  lcd.setTextSize(1);
+  lcd.setCursor(4, 4);
+  lcd.print(title);
+  lcd.drawFastHLine(0, 20, LCD_WIDTH, TFT_ORANGE);
+  lcd.setTextColor(TFT_WHITE, TFT_BLACK);
+}
+
+static void drawChainData() {
+  drawHeader("BITCOIN BLOCK CLOCK");
+
+  if (!dataValid) {
+    lcd.setCursor(4, 40);
+    lcd.setTextColor(TFT_YELLOW, TFT_BLACK);
+    lcd.print("Fetching chain data...");
+    if (lastError.length() > 0) {
+      lcd.setCursor(4, 56);
+      lcd.setTextColor(TFT_RED, TFT_BLACK);
+      lcd.print(lastError);
+    }
+    return;
+  }
+
+  uint32_t halvingBlock = nextHalvingBlock(blockHeight);
+  uint32_t blocksLeft = halvingBlock - blockHeight;
+  uint32_t daysLeft = (blocksLeft * 10) / (60 * 24);  // ~10 min/block
+
+  lcd.setCursor(4, 30);
+  lcd.print("BLOCK HEIGHT");
+  lcd.setCursor(4, 42);
+  lcd.setTextColor(TFT_YELLOW, TFT_BLACK);
+  lcd.setTextSize(2);
+  lcd.printf("%lu", (unsigned long)blockHeight);
+  lcd.setTextSize(1);
+  lcd.setTextColor(TFT_WHITE, TFT_BLACK);
+
+  lcd.drawFastHLine(0, 78, LCD_WIDTH, TFT_DARKGREY);
+  lcd.setCursor(4, 86);
+  lcd.print("NEXT HALVING");
+  lcd.setTextColor(TFT_CYAN, TFT_BLACK);
+  lcd.setCursor(4, 98);
+  lcd.printf("Block %lu\n", (unsigned long)halvingBlock);
+  lcd.setCursor(4, lcd.getCursorY() + 2);
+  lcd.printf("%lu blocks away\n", (unsigned long)blocksLeft);
+  lcd.setCursor(4, lcd.getCursorY() + 2);
+  lcd.printf("~%lu days\n", (unsigned long)daysLeft);
+  lcd.setTextColor(TFT_WHITE, TFT_BLACK);
+
+  lcd.drawFastHLine(0, 148, LCD_WIDTH, TFT_DARKGREY);
+  lcd.setCursor(4, 156);
+  lcd.print("FEES (sat/vB)");
+  lcd.setCursor(4, 168);
+  lcd.setTextColor(TFT_GREEN, TFT_BLACK);
+  lcd.printf("Fast:      %lu\n", (unsigned long)feeFast);
+  lcd.setCursor(4, lcd.getCursorY() + 2);
+  lcd.setTextColor(TFT_YELLOW, TFT_BLACK);
+  lcd.printf("Half-hour: %lu\n", (unsigned long)feeHalfHour);
+  lcd.setCursor(4, lcd.getCursorY() + 2);
+  lcd.setTextColor(TFT_LIGHTGREY, TFT_BLACK);
+  lcd.printf("Hour:      %lu\n", (unsigned long)feeHour);
+
+  lcd.setTextColor(TFT_DARKGREY, TFT_BLACK);
+  lcd.setCursor(4, LCD_HEIGHT - 16);
+  lcd.print("mempool.space, refreshed 60s");
+}
+
+void setup() {
+  Serial.begin(115200);
+
+  lcd.init();
+  lcd.setRotation(0);
+  lcd.setBrightness(200);
+
+  drawHeader("BITCOIN BLOCK CLOCK");
+  lcd.setCursor(4, 40);
+  lcd.print("Connecting to Wi-Fi...");
+
+  WiFi.mode(WIFI_STA);
+  WiFi.begin(WIFI_SSID, WIFI_PASS);
+  for (int i = 0; WiFi.status() != WL_CONNECTED && i < 30; i++) {
+    delay(500);
+    Serial.print(".");
+  }
+
+  if (WiFi.status() != WL_CONNECTED) {
+    drawHeader("BITCOIN BLOCK CLOCK");
+    lcd.setCursor(4, 40);
+    lcd.setTextColor(TFT_RED, TFT_BLACK);
+    lcd.print("Wi-Fi failed.");
+    lcd.setCursor(4, 56);
+    lcd.print("Check WIFI_SSID/WIFI_PASS.");
+    return;
+  }
+  Serial.printf("Wi-Fi connected: %s\n", WiFi.localIP().toString().c_str());
+
+  refreshChainData();
+  drawChainData();
+}
+
+static unsigned long lastPoll = 0;
+
+void loop() {
+  if (WiFi.status() == WL_CONNECTED && millis() - lastPoll >= POLL_INTERVAL_MS) {
+    lastPoll = millis();
+    refreshChainData();
+    drawChainData();
+  }
+}

platformio.ini

@@ -30,3 +30,4 @@ upload_speed  = 921600
 lib_deps =
     lovyan03/LovyanGFX @ ^1.1.16
     adafruit/Adafruit NeoPixel @ ^1.12.3
+    bblanchon/ArduinoJson @ ^7.0.0