Building the Brain — Assembling the IoT Hub Body with an ESP8266 + OLED + Buzzer

const char* ssid     = "YOUR_SSID";     // ← your home router's name here
const char* password = "YOUR_PASSWORD"; // ← your home router's password here

#include <ESP8266WiFi.h>
#include <ESP8266WebServer.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

// =============================================
// 1. Wi-Fi settings (fill these in yourself!)
// =============================================
const char* ssid     = "YOUR_SSID";     // home router name
const char* password = "YOUR_PASSWORD"; // home router password

// Own AP settings for the sensor nodes
const char* ap_ssid     = "IoT_Hub_Net";
const char* ap_password = "iothub1234"; // password for sensor nodes to connect

// =============================================
// 2. Hardware pins
// =============================================
#define BUZZER_PIN    13  // D7 (GPIO13)
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_ADDR    0x3C

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);
ESP8266WebServer server(80);

// =============================================
// 3. 20 memory slots
// =============================================
#define SLOT_COUNT 20
String slot[SLOT_COUNT] = {
  "--", "--", "--", "--", "--",
  "--", "--", "--", "--", "--",
  "--", "--", "--", "--", "--",
  "--", "--", "--", "--", "--"
};

const char* label[SLOT_COUNT] = {
  "Living Temp","Living Hum","Outside Temp","AC",
  "Boiler","Stove","Gas Leak","Fire",
  "Front Door","Door Lock","Living Light","Fridge Temp",
  "CO2","Dust PM2.5","Power","Water",
  "Hot Water","Rain","Bath Hum","Pet Bowl"
};

// =============================================
// 4. Timer variables
// =============================================
unsigned long lastScroll = 0;
unsigned long lastBuzzer = 0;
int scrollOffset = 0;
const int ITEMS_PER_PAGE = 4;
const int SCROLL_INTERVAL = 3000;
bool warningActive = false;

// =============================================
// setup
// =============================================
void setup() {
  Serial.begin(115200);

  // Buzzer init
  pinMode(BUZZER_PIN, OUTPUT);
  digitalWrite(BUZZER_PIN, LOW);

  // OLED init
  Wire.begin(4, 5); // SDA=D2(GPIO4), SCL=D1(GPIO5)
  if (!display.begin(SSD1306_SWITCHCAPVCC, OLED_ADDR)) {
    Serial.println("OLED init failed");
    while (1) yield();
  }
  display.clearDisplay();
  display.setTextColor(WHITE);
  display.setTextWrap(false);

  // Boot logo
  display.setTextSize(1);
  display.setCursor(10, 20);
  display.println("IoT Hub v2.0");
  display.setCursor(15, 40);
  display.println("iothub.co.kr");
  display.display();
  delay(1000);

  // ── Wi-Fi: connect to the home router in STA mode ──
  WiFi.mode(WIFI_AP_STA); // AP + STA simultaneous mode
  WiFi.begin(ssid, password);

  display.clearDisplay();
  display.setCursor(0, 0);
  display.println("WiFi connecting...");
  display.display();

  Serial.print("Connecting to WiFi");
  int dots = 0;
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
    display.setCursor(dots * 6, 16);
    display.print(".");
    display.display();
    dots++;
    if (dots > 20) dots = 0; // fake a line break
  }
  Serial.println();
  Serial.print("STA IP: ");
  Serial.println(WiFi.localIP());

  // ── Soft AP: create own WiFi for the sensor nodes ──
  WiFi.softAP(ap_ssid, ap_password);
  Serial.print("AP  IP: ");
  Serial.println(WiFi.softAPIP());

  // ── Web server routing ──
  server.on("/set", handleSet);
  server.on("/", handleRoot);
  server.on("/status", handleStatus);
  server.onNotFound(handleNotFound);
  server.begin();
  Serial.println("HTTP server started");

  // ── Show the IP on the OLED ──
  display.clearDisplay();
  display.setTextSize(1);
  display.setCursor(0, 0);
  display.println("IoT Hub Ready");
  display.setCursor(0, 14);
  display.print("LAN: ");
  display.println(WiFi.localIP());
  display.setCursor(0, 28);
  display.print("AP : ");
  display.println(WiFi.softAPIP());
  display.setCursor(0, 46);
  display.println("/set?no1=25.5");
  display.println("  to send data");
  display.display();
  delay(3000);
}

// =============================================
// loop
// =============================================
void loop() {
  server.handleClient();
  updateOLED();
  updateBuzzer();
}

// =============================================
// Check warning state
// =============================================
bool checkWarning() {
  for (int i = 0; i < SLOT_COUNT; i++) {
    // slots 7 (gas leak), 8 (fire), 9 (front door open) → warn if not 0
    if ((i == 6 || i == 7 || i == 8)
        && slot[i] != "0" && slot[i] != "--") {
      return true;
    }
    // slot 20 (dog food bowl) → warn if under 50g
    if (i == 19 && slot[i] != "--" && slot[i].toInt() < 50) {
      return true;
    }
  }
  return false;
}

// =============================================
// Buzzer control (beep every 500ms when warning)
// =============================================
void updateBuzzer() {
  warningActive = checkWarning();
  if (warningActive) {
    unsigned long now = millis();
    if (now - lastBuzzer < 500) return;
    lastBuzzer = now;
    digitalWrite(BUZZER_PIN, !digitalRead(BUZZER_PIN));
  } else {
    digitalWrite(BUZZER_PIN, LOW);
  }
}

// =============================================
// GET /set?no1=value&no2=value ...
// =============================================
void handleSet() {
  int updated = 0;
  for (int i = 1; i <= SLOT_COUNT; i++) {
    String paramName = "no" + String(i);
    if (server.hasArg(paramName)) {
      slot[i - 1] = server.arg(paramName);
      updated++;
      Serial.printf("Slot %d (%s) <- %s\n",
                    i, label[i - 1], slot[i - 1].c_str());
    }
  }
  String msg = "{\"updated\":" + String(updated) + "}";
  server.send(200, "application/json", msg);
}

// =============================================
// GET /  → HTML dashboard
// =============================================
void handleRoot() {
  String html = "<!DOCTYPE html>\n"
  "<html lang=\"ko\">\n"
  "<head>\n"
  "<meta charset=\"UTF-8\">\n"
  "<meta name=\"viewport\" content=\"width=device-width,initial-scale=1.0\">\n"
  "<title>IoT Hub</title>\n"
  "<style>\n"
  "*{margin:0;padding:0;box-sizing:border-box;}\n"
  "body{font-family:system-ui,sans-serif;background:#1a1a2e;color:#eee;padding:16px;}\n"
  "h1{text-align:center;font-size:1.3rem;margin-bottom:4px;color:#e94560;}\n"
  ".sub{text-align:center;font-size:0.7rem;color:#555;margin-bottom:16px;}\n"
  ".grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(185px,1fr));gap:10px;}\n"
  ".card{background:#16213e;border-radius:8px;padding:12px;border-left:4px solid #0f3460;}\n"
  ".card.warn{border-left-color:#e94560;background:#1c0e1a;}\n"
  ".card .no{font-size:0.6rem;color:#555;margin-bottom:2px;}\n"
  ".card .label{font-size:0.8rem;color:#a0a0b0;margin-bottom:4px;}\n"
  ".card .value{font-size:1.2rem;font-weight:700;}\n"
  ".footer{text-align:center;margin-top:16px;font-size:0.7rem;color:#444;}\n"
  "</style>\n"
  "</head>\n"
  "<body>\n"
  "<h1>IoT Hub</h1>\n"
  "<div class=\"sub\">iothub.co.kr</div>\n"
  "<div class=\"grid\">\n";

  for (int i = 0; i < SLOT_COUNT; i++) {
    bool isWarn = false;
    String val = slot[i];
    if ((i == 6 || i == 7 || i == 8) && val != "0" && val != "--") isWarn = true;
    if (i == 19 && val != "--" && val.toInt() < 50) isWarn = true;

    html += "<div class=\"card" + String(isWarn ? " warn" : "") + "\">";
    html += "<div class=\"no\">#" + String(i + 1) + "</div>";
    html += "<div class=\"label\">" + String(label[i]) + "</div>";
    html += "<div class=\"value\">" + val + "</div>";
    html += "</div>\n";
  }

  html += "</div>\n"
  "<div class=\"footer\">30s auto-refresh | IoT Hub on ESP8266</div>\n"
  "<script>setTimeout(()=>location.reload(),30000);</script>\n"
  "</body>\n</html>";

  server.send(200, "text/html; charset=utf-8", html);
}

// =============================================
// GET /status → JSON
// =============================================
void handleStatus() {
  String json = "{";
  for (int i = 0; i < SLOT_COUNT; i++) {
    if (i > 0) json += ",";
    json += "\"no" + String(i + 1) + "\":\"" + slot[i] + "\"";
  }
  json += ",\"warning\":" + String(warningActive ? "true" : "false") + "}";
  server.send(200, "application/json", json);
}

// =============================================
// 404
// =============================================
void handleNotFound() {
  server.send(404, "text/plain",
    "404 - Use /set?no1=value  or  /  or  /status");
}

// =============================================
// OLED auto-scroll + invert on warning
// =============================================
void updateOLED() {
  unsigned long now = millis();
  if (now - lastScroll < SCROLL_INTERVAL) return;
  lastScroll = now;

  display.clearDisplay();

  // Top bar
  display.setTextSize(1);
  display.fillRect(0, 0, SCREEN_WIDTH, 10, WHITE);
  display.setTextColor(BLACK);
  display.setCursor(2, 1);
  display.printf("IoT Hub [%d/%d]",
    scrollOffset / ITEMS_PER_PAGE + 1,
    (SLOT_COUNT + ITEMS_PER_PAGE - 1) / ITEMS_PER_PAGE);
  display.setTextColor(WHITE);

  // Body: 4 at a time
  for (int i = 0; i < ITEMS_PER_PAGE; i++) {
    int idx = scrollOffset + i;
    if (idx >= SLOT_COUNT) break;

    int y = 14 + i * 12;
    String val = slot[idx];

    bool isWarn = false;
    if ((idx == 6 || idx == 7 || idx == 8) && val != "0" && val != "--")
      isWarn = true;
    if (idx == 19 && val != "--" && val.toInt() < 50)
      isWarn = true;

    display.setCursor(0, y);
    display.print(label[idx]);
    display.print(":");

    if (isWarn) {
      display.fillRect(80, y, SCREEN_WIDTH - 80, 8, WHITE);
      display.setTextColor(BLACK);
    }
    display.setCursor(82, y);
    display.print(val);
    display.setTextColor(WHITE);
  }

  display.display();

  scrollOffset += ITEMS_PER_PAGE;
  if (scrollOffset >= SLOT_COUNT) scrollOffset = 0;
}