ESP32 MQTT Sensor Dashboard

/*
 * ESP32 MQTT Sensor Dashboard — Beginner
 * Publishes DHT22 temp & humidity to MQTT every 30 seconds.
 * View live data in Node-RED, MQTT Explorer, or any subscriber.
 *
 * Setup:
 *   1) Install Mosquitto broker on your network
 *   2) Install Node-RED + node-red-dashboard
 *   3) Import the Node-RED flow from the project page
 *   4) Update SSID, PASSWORD, BROKER below
 *
 * Library: DHT (Adafruit), PubSubClient (Nick O'Leary)
 */
#include <WiFi.h>
#include <PubSubClient.h>
#include <DHT.h>

const char* SSID     = "YOUR_WIFI_SSID";
const char* PASSWORD = "YOUR_WIFI_PASSWORD";
const char* BROKER   = "192.168.1.100";   // Your broker IP
const int   PORT     = 1883;

#define DHT_PIN  4
#define DHT_TYPE DHT22

// MQTT Topics (change "room1" to identify this sensor's location)
const char* TOPIC_TEMP = "esp32engine/sensors/room1/temperature";
const char* TOPIC_HUM  = "esp32engine/sensors/room1/humidity";
const char* TOPIC_AVAIL= "esp32engine/sensors/room1/availability";

DHT dht(DHT_PIN, DHT_TYPE);
WiFiClient net;
PubSubClient mqtt(net);

void connectMQTT() {
  while (!mqtt.connected()) {
    Serial.print("Connecting MQTT... ");
    // Last Will: publish "offline" if we disconnect unexpectedly
    if (mqtt.connect("esp32-room1", "", "", TOPIC_AVAIL, 0, true, "offline")) {
      mqtt.publish(TOPIC_AVAIL, "online", true);
      Serial.println("connected");
    } else {
      Serial.printf("failed rc=%d — retry in 5sn", mqtt.state());
      delay(5000);
    }
  }
}

void setup() {
  Serial.begin(115200);
  dht.begin();
  WiFi.begin(SSID, PASSWORD);
  Serial.print("Connecting Wi-Fi");
  while (WiFi.status() != WL_CONNECTED) { delay(400); Serial.print("."); }
  Serial.printf("nConnected: %sn", WiFi.localIP().toString().c_str());
  mqtt.setServer(BROKER, PORT);
  connectMQTT();
}

void loop() {
  if (!mqtt.connected()) connectMQTT();
  mqtt.loop();

  static unsigned long last = 0;
  if (millis() - last >= 30000) {
    last = millis();
    float h = dht.readHumidity();
    float t = dht.readTemperature();
    if (!isnan(h) && !isnan(t)) {
      mqtt.publish(TOPIC_TEMP, String(t, 2).c_str(), true);
      mqtt.publish(TOPIC_HUM,  String(h, 2).c_str(), true);
      Serial.printf("Published: temp=%.2f  hum=%.2fn", t, h);
    }
  }
}