Quickstart: Send telemetry from a device to an IoT hub and read it with a back-end application (C)

IoT Hub is an Azure service that enables you to ingest high volumes of telemetry from your IoT devices into the cloud for storage or processing. In this quickstart, you send telemetry from a simulated device application, through IoT Hub, to a back-end application for processing.

The quickstart uses a C sample application from the Azure IoT device SDK for C to send telemetry to an IoT hub. The Azure IoT device SDKs are written in ANSI C (C99) for portability and broad platform compatibility. Before running the sample code, you will create an IoT hub and register the simulated device with that hub.

This article is written for Windows, but you can complete this quickstart on Linux as well.

Use Azure Cloud Shell

Azure hosts Azure Cloud Shell, an interactive shell environment that you can use through your browser. You can use either Bash or PowerShell with Cloud Shell to work with Azure services. You can use the Cloud Shell preinstalled commands to run the code in this article without having to install anything on your local environment.

To start Azure Cloud Shell:

Option Example/Link
Select Try It in the upper-right corner of a code block. Selecting Try It doesn't automatically copy the code to Cloud Shell. Example of Try It for Azure Cloud Shell
Go to https://shell.azure.com, or select the Launch Cloud Shell button to open Cloud Shell in your browser. Launch Cloud Shell in a new window
Select the Cloud Shell button on the top-right menu bar in the Azure portal. Cloud Shell button in the Azure portal

To run the code in this article in Azure Cloud Shell:

  1. Start Cloud Shell.

  2. Select the Copy button on a code block to copy the code.

  3. Paste the code into the Cloud Shell session by selecting Ctrl+Shift+V on Windows and Linux or by selecting Cmd+Shift+V on macOS.

  4. Select Enter to run the code.

If you don’t have an Azure subscription, create a free account before you begin.

Prerequisites

  • Install Visual Studio 2019 with the 'Desktop development with C++' workload enabled.

  • Install the latest version of Git.

  • Run the following command to add the Microsoft Azure IoT Extension for Azure CLI to your Cloud Shell instance. The IOT Extension adds IoT Hub, IoT Edge, and IoT Device Provisioning Service (DPS) specific commands to Azure CLI.

    az extension add --name azure-cli-iot-ext
    

Prepare the development environment

For this quickstart, you'll be using the Azure IoT device SDK for C.

For the following environments, you can use the SDK by installing these packages and libraries:

  • Linux: apt-get packages are available for Ubuntu 16.04 and 18.04 using the following CPU architectures: amd64, arm64, armhf, and i386. For more information, see Using apt-get to create a C device client project on Ubuntu.

  • mbed: For developers creating device applications on the mbed platform, we've published a library and samples that will get you started in minutes witH Azure IoT Hub. For more information, see Use the mbed library.

  • Arduino: If you're developing on Arduino, you can leverage the Azure IoT library available in the Arduino IDE library manager. For more information, see The Azure IoT Hub library for Arduino.

  • iOS: The IoT Hub Device SDK is available as CocoaPods for Mac and iOS device development. For more information, see iOS Samples for Microsoft Azure IoT.

However, in this quickstart, you'll prepare a development environment used to clone and build the Azure IoT C SDK from GitHub. The SDK on GitHub includes the sample code used in this quickstart.

  1. Download the CMake build system.

    It's important that the Visual Studio prerequisites (Visual Studio and the 'Desktop development with C++' workload) are installed on your machine, before starting the CMake installation. Once the prerequisites are in place, and the download is verified, install the CMake build system.

  2. Open a command prompt or Git Bash shell and navigate to a working directory that you want to clone the Azure IoT C SDK into. Execute the following command to clone the Azure IoT C SDK GitHub repository:

    git clone https://github.com/Azure/azure-iot-sdk-c.git --recursive
    

    You should expect this operation to take several minutes to complete.

  3. Create a cmake subdirectory in the root directory of the git repository, and navigate to that folder. Enter the following commands from your working directory:

    cd azure-iot-sdk-c
    mkdir cmake
    cd cmake
    
  4. Run the following command to build a version of the SDK specific to your development client platform. A Visual Studio solution for the simulated device will be generated in the cmake directory.

    cmake ..
    

    If cmake doesn't find your C++ compiler, you might get build errors while running the above command. If that happens, try running this command in the Visual Studio command prompt.

    Once the build succeeds, the last few output lines will look similar to the following output:

    $ cmake ..
    -- Building for: Visual Studio 15 2017
    -- Selecting Windows SDK version 10.0.16299.0 to target Windows 10.0.17134.
    -- The C compiler identification is MSVC 19.12.25835.0
    -- The CXX compiler identification is MSVC 19.12.25835.0
    
    ...
    
    -- Configuring done
    -- Generating done
    -- Build files have been written to: E:/IoT Testing/azure-iot-sdk-c/cmake
    

Create an IoT hub

This section describes how to create an IoT hub using the Azure portal.

  1. Sign in to the Azure portal.

  2. From the Azure homepage, select the + Create a resource button, and then enter IoT Hub in the Search the Marketplace field.

  3. Select IoT Hub from the search results, and then select Create.

  4. On the Basics tab, complete the fields as follows:

    • Subscription: Select the subscription to use for your hub.

    • Resource Group: Select a resource group or create a new one. To create a new one, select Create new and fill in the name you want to use. To use an existing resource group, select that resource group. For more information, see Manage Azure Resource Manager resource groups.

    • Region: Select the region in which you want your hub to be located. Select the location closest to you.

    • IoT Hub Name: Enter a name for your hub. This name must be globally unique. If the name you enter is available, a green check mark appears.

    Important

    Because the IoT hub will be publicly discoverable as a DNS endpoint, be sure to avoid entering any sensitive or personally identifiable information when you name it.

    Create a hub in the Azure portal

  5. Select Next: Size and scale to continue creating your hub.

    Set the size and scale for a new hub using the Azure portal

    This screen allows you to set the following values:

    • Pricing and scale tier: Your selected tier. You can choose from several tiers, depending on how many features you want and how many messages you send through your solution per day. The free tier is intended for testing and evaluation. It allows 500 devices to be connected to the hub and up to 8,000 messages per day. Each Azure subscription can create one IoT hub in the free tier.

    • IoT Hub units: The number of messages allowed per unit per day depends on your hub's pricing tier. For example, if you want the hub to support ingress of 700,000 messages, you choose two S1 tier units. For details about the other tier options, see Choosing the right IoT Hub tier.

    • Advanced Settings > Device-to-cloud partitions: This property relates the device-to-cloud messages to the number of simultaneous readers of the messages. Most hubs need only four partitions.

  6. For this article, accept the default choices, and then select Review + create to review your choices. You see something similar to this screen.

    Review information for creating the new hub

  7. Select Create to create your new hub. Creating the hub takes a few minutes.

Register a device

A device must be registered with your IoT hub before it can connect. In this section, you'll use the Azure Cloud Shell with the IoT extension to register a simulated device.

  1. Run the following command in Azure Cloud Shell to create the device identity.

    YourIoTHubName: Replace this placeholder below with the name you chose for your IoT hub.

    MyCDevice: This is the name of the device you're registering. It's recommended to use MyCDevice as shown. If you choose a different name for your device, you'll also need to use that name throughout this article, and update the device name in the sample applications before you run them.

    az iot hub device-identity create --hub-name {YourIoTHubName} --device-id MyCDevice
    
  2. Run the following command in Azure Cloud Shell to get the device connection string for the device you just registered:

    YourIoTHubName: Replace this placeholder below with the name you chose for your IoT hub.

    az iot hub device-identity show-connection-string --hub-name {YourIoTHubName} --device-id MyCDevice --output table
    

    Make a note of the device connection string, which looks like:

    HostName={YourIoTHubName}.azure-devices.net;DeviceId=MyCDevice;SharedAccessKey={YourSharedAccessKey}

    You'll use this value later in the quickstart.

Send simulated telemetry

The simulated device application connects to a device-specific endpoint on your IoT hub and sends a string as simulated telemetry.

  1. Using a text editor, open the iothub_convenience_sample.c source file and review the sample code for sending telemetry. The file is located in the following location under the working directory where you cloned the Azure IoT C SDK:

    azure-iot-sdk-c\iothub_client\samples\iothub_convenience_sample\iothub_convenience_sample.c
    
  2. Find the declaration of the connectionString constant:

    /* Paste in your device connection string  */
    static const char* connectionString = "[device connection string]";
    

    Replace the value of the connectionString constant with the device connection string you made a note of earlier. Then save your changes to iothub_convenience_sample.c.

  3. In a local terminal window, navigate to the iothub_convenience_sample project directory in the CMake directory that you created in the Azure IoT C SDK. Enter the following command from your working directory:

    cd azure-iot-sdk-c/cmake/iothub_client/samples/iothub_convenience_sample
    
  4. Run CMake in your local terminal window to build the sample with your updated connectionString value:

    cmake --build . --target iothub_convenience_sample --config Debug
    
  5. In your local terminal window, run the following command to run the simulated device application:

    Debug\iothub_convenience_sample.exe
    

    The following screenshot shows the output as the simulated device application sends telemetry to the IoT hub:

    Run the simulated device

Read the telemetry from your hub

In this section, you'll use the Azure Cloud Shell with the IoT extension to monitor the device messages that are sent by the simulated device.

  1. Using the Azure Cloud Shell, run the following command to connect and read messages from your IoT hub:

    YourIoTHubName: Replace this placeholder below with the name you choose for your IoT hub.

    az iot hub monitor-events --hub-name {YourIoTHubName} --output table
    

    Read the device messages using the Azure CLI

Clean up resources

If you will be continuing to the next recommended article, you can keep the resources you've already created and reuse them.

Otherwise, you can delete the Azure resources created in this article to avoid charges.

Important

Deleting a resource group is irreversible. The resource group and all the resources contained in it are permanently deleted. Make sure that you do not accidentally delete the wrong resource group or resources. If you created the IoT Hub inside an existing resource group that contains resources you want to keep, only delete the IoT Hub resource itself instead of deleting the resource group.

To delete a resource group by name:

  1. Sign in to the Azure portal and select Resource groups.

  2. In the Filter by name textbox, type the name of the resource group containing your IoT Hub.

  3. To the right of your resource group in the result list, select ... then Delete resource group.

    Delete

  4. You will be asked to confirm the deletion of the resource group. Type the name of your resource group again to confirm, and then select Delete. After a few moments, the resource group and all of its contained resources are deleted.

Next steps

In this quickstart, you set up an IoT hub, registered a device, sent simulated telemetry to the hub using a C application, and read the telemetry from the hub using the Azure Cloud Shell.

To learn more about developing with the Azure IoT Hub C SDK, continue to the following How-to guide: