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

Article
02/03/2023

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.

If you don't have an Azure subscription, create a trial account before you begin.

Install Visual Studio 2019 with the 'Desktop development with C++' workload enabled.
Install the latest version of Git.
Make sure that port 8883 is open in your firewall. The device sample in this quickstart uses MQTT protocol, which communicates over port 8883. This port may be blocked in some corporate and educational network environments. For more information and ways to work around this issue, see Connecting to IoT Hub (MQTT).

You can use the local Azure CLI.

If you prefer, install the Azure CLI to run CLI reference commands.
Local Azure CLI, see how to install the Azure CLI. If you're running on Windows or macOS, consider running Azure CLI in a Docker container. For more information, see How to run the Azure CLI in a Docker container.
- Sign in to the Azure CLI by using the az login command. To finish the authentication process, follow the steps displayed in your terminal. For other sign-in options, see Sign in with the Azure CLI.
- When you're prompted, install the Azure CLI extension on first use. For more information about extensions, see Use extensions with the Azure CLI.
- Run az version to find the version and dependent libraries that are installed. To upgrade to the latest version, run az upgrade.

Note

This article uses the newest version of the Azure IoT extension, called azure-iot. The legacy version is called azure-cli-iot-ext.You should only have one version installed at a time. You can use the command az extension list to validate the currently installed extensions.

Use az extension remove --name azure-cli-iot-ext to remove the legacy version of the extension.

Use az extension add --name azure-iot to add the new version of the extension.

To see what extensions you have installed, use az extension list.

Install all dependencies before building the SDK.

sudo apt-get update    
sudo apt-get install -y git cmake build-essential curl libcurl4-openssl-dev libssl-dev uuid-dev ca-certificates

Verify that CMake is at least version 2.8.12:
```
cmake --version
```
Verify that gcc is at least version 4.4.7:
```
gcc --version
```
Make sure that port 8883 is open in your firewall. The device sample in this quickstart uses MQTT protocol, which communicates over port 8883. This port may be blocked in some corporate and educational network environments. For more information and ways to work around this issue, see Connecting to IoT Hub (MQTT).

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:

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 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.

Windows
Linux

Download the CMake build system.

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.
Find the tag name for the latest release of the SDK.
Open a command prompt or Git Bash shell. Run the following commands to clone the latest release of the Azure IoT C SDK GitHub repository. Use the tag you found in the previous step as the value for the -b parameter:
```
git clone -b <release-tag> https://github.com/Azure/azure-iot-sdk-c.git
cd azure-iot-sdk-c
git submodule update --init
```
You should expect this operation to take several minutes to complete.
Create a cmake subdirectory in the root directory of the git repository, and navigate to that folder. Run the following commands from the azure-iot-sdk-c directory:
```
mkdir cmake
cd cmake
```
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
```

Find the tag name for the latest release of the SDK.
Open a shell command prompt. Run the following commands to clone the latest release of the Azure IoT C SDK GitHub repository. Use the tag you found in the previous step as the value for the -b parameter:
```
git clone -b <release-tag> https://github.com/Azure/azure-iot-sdk-c.git
cd azure-iot-sdk-c
git submodule update --init
```
Create a cmake subdirectory in the root directory of the git repository, and navigate to that folder. Run the following commands from the azure-iot-sdk-c directory:
```
mkdir cmake
cd cmake
```
Run the following command to build a version of the SDK specific to your development client platform.
```
cmake ..
cmake --build .
```

Create an IoT hub

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

Sign in to the Azure portal.
On the Azure homepage, select the + Create a resource button.
From the Categories menu, select Internet of Things, and then select IoT Hub.

On the Basics tab, complete the fields as follows:

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.

Property	Value
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.
IoT hub name	Enter a name for your hub. This name must be globally unique, with a length between 3 and 50 alphanumeric characters. The name can also include the dash (`'-'`) character.
Region	Select the region, closest to you, where you want your hub to be located. Some features, such as IoT Hub device streams, are only available in specific regions. For these limited features, you must select one of the supported regions.
Tier	Select the tier that you want to use for your hub. Tier selection depends 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. The free tier 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. To compare the features available to each tier, select Compare tiers. For more information, see Choose the right IoT Hub tier for your solution.
Daily message limit	Select the maximum daily quota of messages for your hub. The available options depend on the tier you've selected for your hub. To see the available messaging and pricing options, select See all options and select the option that best matches the needs of your hub. For more information, see IoT Hub quotas and throttling.

Screen capture that shows how to create an IoT hub in the Azure portal.

Select Next: Networking to continue creating your hub.

On the Networking tab, complete the fields as follows:

Property	Value
Connectivity configuration	Choose the endpoints that devices can use to connect to your IoT hub. Accept the default setting, Public endpoint, for this example. You can change this setting after the IoT hub is created. For more information, see Managing public network access for your IoT hub.

Screen capture that shows how to choose the endpoints that can connect to a new IoT hub.

Select Next: Management to continue creating your hub.

Accept the default settings here. If desired, you can modify any of the following fields:
- Pricing and scale tier: Tier selection depends 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. The free tier 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. For details about other tier options, see Choosing the right IoT Hub tier.
  
  If you're working through a quickstart, select 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, choose two S1 tier units.
- Role-based access control: This property decides how you manage access to your IoT hub. Allow shared access policies or choose only role-based access control. For more information, see Control access to IoT Hub by using Azure Active Directory.
- 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.
Note

Prices shown are for example purposes only.
Select Next: Tags to continue to the next screen.

Tags are name/value pairs. You can assign the same tag to multiple resources and resource groups to categorize resources and consolidate billing. In this document, you won't be adding any tags. For more information, see Use tags to organize your Azure resources.
Select Next: Review + create to review your choices.
Select Create to start the deployment of your new hub. Your deployment will be in progress a few minutes while the hub is being created. Once the deployment is complete, select Go to resource to open the new hub.

Register a device

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

Run the following commands 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
```
Run the following commands 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 connection-string show --hub-name {YourIoTHubName} --device-id MyCDevice --output table
```
Make a note of the device connection string, which looks like:

HostName={YourIoTHubName}.azure-devices.cn;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.

Windows
Linux

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
```
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.
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
```
Run CMake in your local terminal window to build the sample with your updated connectionString value:
```
cmake --build . --target iothub_convenience_sample --config Debug
```
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:

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
```
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.
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
```
Run CMake in your local terminal window to build the sample with your updated connectionString value:
```
cmake --build . --target iothub_convenience_sample
```
In your local terminal window, run the following command to run the simulated device application:
```
./iothub_convenience_sample
```
The following screenshot shows the output as the simulated device application sends telemetry to the IoT hub:

Read the telemetry from your hub

In this section, you will use the Azure CLI with the IoT extension to monitor the device messages that are sent by the simulated device.

Using the Azure CLI, 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
```

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:

Sign in to the Azure portal and select Resource groups.
In the Filter by name textbox, type the name of the resource group containing your IoT Hub.
To the right of your resource group in the result list, select ... then Delete resource group.
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 CLI.

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

Develop using Azure IoT Hub C SDK