Quickstart: Send telemetry from a device to an IoT hub and read the telemetry from the hub 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 written for Windows but you can complete this quickstart on Linux as well.

Open Azure Cloud Shell

Azure Cloud Shell is a free, interactive shell that you can use to run the steps in this article. Common Azure tools are preinstalled and configured in Cloud Shell for you to use with your account. Just select the Copy button to copy the code, paste it in Cloud Shell, and then press Enter to run it. There are a few ways to open Cloud Shell:

Select Try It in the upper-right corner of a code block. Cloud Shell in this article
Open Cloud Shell in your browser. https://shell.azure.com/bash
Select the Cloud Shell button on the menu in the upper-right corner of the Azure portal. Cloud Shell in the portal

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

Prerequisites

Prepare the development environment

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

You can use the SDK by installing the packages and libraries for the following environments:

  • 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 have 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 are 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 will 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 version 3.11.4 of the CMake build system. Verify the downloaded binary using the corresponding cryptographic hash value. The following example used Windows PowerShell to verify the cryptographic hash for version 3.11.4 of the x64 MSI distribution:

    PS C:\Downloads> $hash = get-filehash .\cmake-3.11.4-win64-x64.msi
    PS C:\Downloads> $hash.Hash -eq "56e3605b8e49cd446f3487da88fcc38cb9c3e9e99a20f5d4bd63e54b7a35f869"
    True
    

    The following hash values for version 3.11.4 were listed on the CMake site at the time of this writing:

    6dab016a6b82082b8bcd0f4d1e53418d6372015dd983d29367b9153f1a376435  cmake-3.11.4-Linux-x86_64.tar.gz
    72b3b82b6d2c2f3a375c0d2799c01819df8669dc55694c8b8daaf6232e873725  cmake-3.11.4-win32-x86.msi
    56e3605b8e49cd446f3487da88fcc38cb9c3e9e99a20f5d4bd63e54b7a35f869  cmake-3.11.4-win64-x64.msi
    

    It is 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. 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
    

    The size of this repository is currently around 220 MB. 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.

    cd azure-iot-sdk-c
    mkdir cmake
    cd cmake
    
  4. Run the following command that builds 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 does not 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. Log in to the Azure portal.

  2. Choose +Create a resource, then choose Internet of Things.

  3. Click Iot Hub from the list on the right. You see the first screen for creating an IoT hub.

    Screenshot showing creating a hub in the Azure portal

    Fill in the fields.

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

    Resource Group: You can create a new resource group or use an existing one. To create a new one, click Create new and fill in the name you want to use. To use an existing resource group, click Use existing and select the resource group from the dropdown list. For more information, see Use resource groups to manage your Azure resources.

    Region: This is the region in which you want your hub to be located. Select the location closest to you from the dropdown list.

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

    Important

    The IoT hub will be publicly discoverable as a DNS endpoint, so make sure to avoid any sensitive information while naming it.

  4. Click Next: Size and scale to continue creating your IoT hub.

    Screenshot showing setting size and scale for a new IoT hub using the Azure portal

    On this screen, you can take the defaults and just click Review + create at the bottom.

    Pricing and scale 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 IoT 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 IoT 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 / Device-to-cloud partitions: This property relates the device-to-cloud messages to the number of simultaneous readers of the messages. Most IoT hubs only need four partitions.

  5. Click Review + create to review your choices. You see something similar to this screen.

    Screenshot reviewing information for creating the new IoT hub

  6. Click Create to create your new IoT 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 will use the Azure Cloud Shell with the IoT extension to register a simulated device.

  1. Run the following commands in Azure Cloud Shell to add the IoT Hub CLI extension and to create the device identity.

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

    MyCDevice : This is the name given for the registered device. Use MyCDevice as shown. If you choose a different name for your device, you will also need to use that name throughout this article, and update the device name in the sample applications before you run them.

    az extension add --name azure-cli-iot-ext
    az iot hub device-identity create --hub-name YourIoTHubName --device-id MyCDevice
    
  2. Run the following commands 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 choose 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=MyNodeDevice;SharedAccessKey={YourSharedAccessKey}

    You 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:

    \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 previously. 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.

    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 a 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 will 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 click 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, click ... 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 click Delete. After a few moments, the resource group and all of its contained resources are deleted.

Next steps

In this quickstart, you've setup 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: