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Lab 2.4: Send cloud-to-device messages

In this lab, you deploy a sample application on Raspberry Pi 3. The sample application monitors incoming messages from your IoT hub. You also run a gulp task on your computer to send messages to Pi from your IoT hub. When the sample application receives the messages, it blinks the LED.

What you will do

  • Connect the sample application to your IoT hub.
  • Deploy and run the sample application.
  • Send messages from your IoT hub to Pi to blink the LED.

What you will learn

In this article, you will learn:

  • How to monitor incoming messages from your IoT hub
  • How to send cloud-to-device messages from your IoT hub to Pi.

What you need

Connect the sample application to your IoT hub

  1. Make sure that you're in the repo folder iot-hub-node-raspberrypi-getting-started. Open the sample application in Visual Studio Code by running the following commands:

    cd Lesson4
code .

    Notice the app.js file in the app subfolder. The app.js file is the key source file that contains the code to monitor incoming messages from the IoT hub. The blinkLED function blinks the LED.

    Repo structure in the sample application

  2. Initialize the configuration file by using the following commands:

    npm install
gulp init

    If you completed the steps in Create an Azure function app and storage account on this computer, all the configurations are inherited, so you can skip to the task of deploying and running the sample application. If you completed the steps in Create an Azure function app and storage account on a different computer, you need to replace the placeholders in the config-raspberrypi.json file. The config-raspberrypi.json file is in the subfolder of your home folder.

    Contents of the config-raspberrypi.json file

  • Replace [device hostname or IP address] with the IP address of Pi or the host name that you get by running the devdisco list --eth command.
  • Replace [IoT device connection string] with the device connection string that you get by running the az iot device show-connection-string --hub-name {my hub name} --device-id {device id} -g iot-sample {resource group name} command.
  • Replace [IoT hub connection string] with the IoT hub connection string that you get by running the az iot hub show-connection-string --name {my hub name} -g iot-sample {resource group name} command.

Note

Run gulp install-tools as well, if you haven't done it in Lesson 1.

Deploy and run the application

Deploy and run the sample application on Pi by running the following command:

gulp deploy && gulp run

The command deploys the sample application to Pi. Then, it runs the application on Pi and a separate task on your host computer to send 20 blink messages to Pi from your IoT hub.

After the application runs, it starts listening to messages from your IoT hub. Meanwhile, the gulp task sends several "blink" messages from your IoT hub to Pi. For each blink message that Pi receives, the sample application calls the blinkLED function to blink the LED.

You should see the LED blink every two seconds as the gulp task sends 20 messages from your IoT hub to Pi. The last one is a "stop" message that tells the application to stop running.

application with gulp command and blink messages

Summary

You’ve successfully sent messages from your IoT hub to Pi to blink the LED.

In the next lab you will change the on/off behavior of the LED.

Back to Lab 2 - IoT with Linux and Node.js

Back to IoT Labs homepage

9gag: Sorry for the long post, here's a potato:

9gag Potato