Azure IoT Hub: Device-to-Cloud Messaging

Step 1: Create an Azure IoT Hub

First, you need to provision an IoT Hub instance in Azure. This service acts as the central message hub for your IoT devices.

1. Sign in to the Azure portal.
2. Click "Create a resource".
3. Search for "IoT Hub" and select it.
4. Click "Create".
5. Fill in the required details: Subscription, Resource group, Region, Name (globally unique), and choose a Pricing and scale tier (Free tier is sufficient for testing).
6. Click "Review + create" and then "Create".

Once deployed, navigate to your IoT Hub resource. You will need the Hostname and the Primary connection string for the service later.

Step 2: Register a Device

Each device needs to be registered with your IoT Hub to establish a secure connection. We'll register a simulated device for this tutorial.

1. In your IoT Hub overview page, go to "Devices" under "Explorers".
2. Click "+ Add device".
3. Provide a Device ID (e.g., my-sample-device).
4. Select "Auto-generate keys".
5. Click "Save".

Note down the Device ID and the Primary connection string for this device. This string contains credentials for your device to authenticate with IoT Hub.

Step 3: Set up Your Development Environment

We'll use Node.js to send messages. If you don't have it installed, download it from nodejs.org.

Create a new project directory and initialize a Node.js project:

mkdir iot-device-sender
cd iot-device-sender
npm init -y

Install the Azure IoT device SDK:

npm install azure-iot-device azure-iot-device-mqtt

Step 4: Write the Device Code

Create a file named sendTelemetry.js and add the following code. Replace the placeholder connection string with the one you copied in Step 2.

const Client = require('azure-iot-device').Client;
const Protocol = require('azure-iot-device-mqtt').Mqtt;

// Replace with your device's primary connection string
const connectionString = 'HostName=YOUR_IOT_HUB_HOSTNAME;DeviceId=YOUR_DEVICE_ID;SharedAccessKey=YOUR_DEVICE_KEY';

const client = Client.fromConnectionString(connectionString, Protocol);

function sendTelemetryData() {
    const temperature = 20 + (Math.random() * 10); // Simulate temperature between 20 and 30
    const humidity = 50 + (Math.random() * 20);   // Simulate humidity between 50 and 70

    const message = {
        temperature: temperature.toFixed(2),
        humidity: humidity.toFixed(2)
    };

    const messageString = JSON.stringify(message);

    client.sendEvent(messageString, function (err) {
        if (err) {
            console.error('Failed to send message: ' + err.toString());
        } else {
            console.log('Message sent: ' + messageString);
        }
    });
}

// Connect the client
client.open(function (err) {
    if (err) {
        console.error('Could not connect: ' + err.message);
    } else {
        console.log('Client connected');

        // Send telemetry data every 5 seconds
        setInterval(sendTelemetryData, 5000);
    }
});

Note: Remember to replace 'YOUR_IOT_HUB_HOSTNAME;DeviceId=YOUR_DEVICE_ID;SharedAccessKey=YOUR_DEVICE_KEY' with your actual device connection string.

Step 5: Run the Device Application

Open your terminal in the iot-device-sender directory and run the script:

node sendTelemetry.js

You should see output indicating that messages are being sent.

Step 6: Monitor Messages in IoT Hub

You can monitor the incoming messages to your IoT Hub using various methods. For this tutorial, we'll use the Azure CLI.

1. Install the Azure CLI if you haven't already.
2. Log in to your Azure account: az login
3. Set your subscription: az account set --subscription "Your Subscription Name"
4. Start monitoring events from your IoT Hub. Replace YOUR_IOT_HUB_NAME with the name of your IoT Hub.

az iot hub monitor-events --hub-name YOUR_IOT_HUB_NAME

As your device sends messages, you will see them appear in the Azure CLI output, formatted as JSON.

Alternatively, you can use tools like IoT Explorer from the Visual Studio Code Marketplace for a more graphical interface to monitor messages and device twins.