Arduino + MQTT

What you'll build

A temperature and humidity sensor connected to the internet that sends data to your computer every 5 seconds.

When finished you'll have:

• An ESP32 reading real temperature and humidity from your room
• Data traveling over WiFi to a public MQTT broker
• A script on your computer showing real-time data

This is your first real IoT project. Hardware + Software + Internet.

Shopping list (exact)

You need these specific components:

Total: ~$12-15 USD

Note: DHT22 is more accurate than DHT11. If you can, buy the DHT22.

Wiring diagram

Connect the DHT22 sensor to the ESP32 like this:

    ESP32 DevKit V1                    DHT22
    +--------------+                  +-------+
    |              |                  |       |
    |         3.3V |------ wire ------| VCC   |  (pin 1 - left)
    |              |                  |       |
    |        GPIO4 |------ wire ------| DATA  |  (pin 2)
    |              |                  |       |
    |          GND |------ wire ------| GND   |  (pin 4 - right)
    |              |                  |       |
    +--------------+                  +-------+

    Note: DHT22 pin 3 is not used (leave disconnected)

Connection table:

Important: Use 3.3V, NOT 5V. The ESP32 works at 3.3V.

Step 1: Install Arduino IDE

1. Go to arduino.cc/en/software
2. Download Arduino IDE 2.x for your operating system
3. Install and open Arduino IDE

Step 2: Configure ESP32 in Arduino IDE

ESP32 doesn't come pre-installed. We need to add it:

1. Open Arduino IDE
2. Go to File → Preferences (or Arduino IDE → Settings on Mac)
3. In "Additional boards manager URLs" add:

   https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json
   

4. Click OK
5. Go to Tools → Board → Boards Manager
6. Search "esp32"
7. Install "esp32 by Espressif Systems" (takes 2-3 minutes)

Step 3: Install libraries

You need 2 libraries:

1. Go to Tools → Manage Libraries
2. Search "DHT sensor library" by Adafruit → Install
3. Search "PubSubClient" by Nick O'Leary → Install

If asked about dependencies, accept to install them.

Step 4: Connect the ESP32

1. Connect ESP32 to your computer with USB cable
2. Go to Tools → Board and select "ESP32 Dev Module"
3. Go to Tools → Port and select the port (COM3, COM4 on Windows, or /dev/cu.usbserial on Mac)

Port not showing? You need the CP210x driver:

• Windows/Mac: silabs.com/developers/usb-to-uart-bridge-vcp-drivers

Step 5: The complete code

Create a new sketch and paste this code:

// ============================================
// IoT Sensor: ESP32 + DHT22 + MQTT
// luxIA.us - Complete tutorial
// ============================================

#include <WiFi.h>
#include <PubSubClient.h>
#include <DHT.h>

// --- CONFIGURATION: EDIT THESE VALUES ---
const char* WIFI_SSID = "YOUR_WIFI_NAME";      // Your WiFi name
const char* WIFI_PASS = "YOUR_WIFI_PASSWORD";  // Your WiFi password
const char* MQTT_SERVER = "broker.hivemq.com"; // Public MQTT broker (free)
const int MQTT_PORT = 1883;
const char* MQTT_TOPIC = "luxia/sensor/yourName"; // Change "yourName" to something unique
// ----------------------------------------

// Sensor configuration
#define DHT_PIN 4        // GPIO4 - where you connected DATA
#define DHT_TYPE DHT22   // Change to DHT11 if using that model

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

void setup() {
  // Start serial monitor (to see messages on your computer)
  Serial.begin(115200);
  Serial.println();
  Serial.println("=== IoT Sensor starting ===");

  // Start sensor
  dht.begin();
  Serial.println("DHT sensor started");

  // Connect WiFi
  Serial.print("Connecting to WiFi: ");
  Serial.println(WIFI_SSID);
  WiFi.begin(WIFI_SSID, WIFI_PASS);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println();
  Serial.print("WiFi connected! IP: ");
  Serial.println(WiFi.localIP());

  // Configure MQTT
  mqtt.setServer(MQTT_SERVER, MQTT_PORT);
  Serial.println("MQTT configured");
}

void connectMQTT() {
  while (!mqtt.connected()) {
    Serial.print("Connecting to MQTT...");

    // Create unique ID for this device
    String clientId = "ESP32-" + String(random(0xffff), HEX);

    if (mqtt.connect(clientId.c_str())) {
      Serial.println(" connected!");
    } else {
      Serial.print(" failed, code: ");
      Serial.print(mqtt.state());
      Serial.println(" - retrying in 5 seconds");
      delay(5000);
    }
  }
}

void loop() {
  // Ensure MQTT connection
  if (!mqtt.connected()) {
    connectMQTT();
  }
  mqtt.loop();

  // Read sensor
  float temperature = dht.readTemperature();
  float humidity = dht.readHumidity();

  // Check valid reading
  if (isnan(temperature) || isnan(humidity)) {
    Serial.println("Error reading sensor!");
    delay(2000);
    return;
  }

  // Create JSON message
  String message = "{\"temp\":" + String(temperature, 1) +
                   ",\"hum\":" + String(humidity, 1) + "}";

  // Send via MQTT
  mqtt.publish(MQTT_TOPIC, message.c_str());

  // Show in Serial Monitor
  Serial.print("Sent: ");
  Serial.println(message);

  // Wait 5 seconds
  delay(5000);
}

Step 6: Configure YOUR WiFi

In the code, change these lines with your data:

const char* WIFI_SSID = "YOUR_WIFI_NAME";      // Your WiFi network name
const char* WIFI_PASS = "YOUR_WIFI_PASSWORD";  // Your WiFi password
const char* MQTT_TOPIC = "luxia/sensor/yourName"; // Change yourName

Step 7: Upload the code

1. Click the Upload button (right arrow) in Arduino IDE
2. Wait for compilation (30-60 seconds)
3. Wait for upload to ESP32 (shows "Connecting..." then percentages)
4. When done, open Tools → Serial Monitor
5. Select 115200 baud in the bottom right corner

Step 8: Verify it works

In Serial Monitor you should see:

=== IoT Sensor starting ===
DHT sensor started
Connecting to WiFi: YOUR_WIFI
....
WiFi connected! IP: 192.168.1.105
MQTT configured
Connecting to MQTT... connected!
Sent: {"temp":23.5,"hum":45.2}
Sent: {"temp":23.6,"hum":45.1}
Sent: {"temp":23.5,"hum":45.3}

If you see this, it works! Your sensor is sending data to the internet.

Step 9: View data from your computer

Now let's receive that data on your computer.

Install an MQTT client:

npm install -g mqtt

Subscribe to your topic:

mqtt sub -h broker.hivemq.com -t "luxia/sensor/yourName"

You should see data arriving:

{"temp":23.5,"hum":45.2}
{"temp":23.6,"hum":45.1}

Troubleshooting

Next step

→ Analytics Dashboard - Display this data in charts