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[IoT Home Project] Part 9 - Extending Azure Function to support Thieves Alarm

In this post we will discover how to
  • Crunch distance (sonar) information produced by a GrovePI sensor and send using Raspberry PI and Azure IoT Hub to backend
  • Add filters on top of Service Bus Topic Subscriptions to receive only information related to distance and temperature on each subscription
  • Add new functionality to the current portal to be able to display alarm and notify our user
In this moment we have a system that is able to collect metrics from Raspberry and process some of the data. We already have from GrovePI a sensor that calculate the distance from the sensor to an object. Why not to use it to detect is something is moving in front of it and create a simple alarm system.
Yes, this is not the best sensor that we could use, although this scenario is a great method to learn something new.

Previous post: [IoT Home Project] Part 8 - Connecting to Azure Function and to a virtual heat pump
GitHub source code:

What we have until now
We already developed a system that sends data from our sonar (distance sensor) to Azure IoT Hub. From there there is a Stream Analytic job query that push our data to Service Bus Topic. It means that we already have all that we need in Azur and we just need to interpret data and create a notification system.
Below is an overview of the components that are involved, where green border marks a component that needs to be developed.

Filter messages on Service Bus Topic per Subscription
The base concept is to add a filter on each subscription, that would allow only specific messages to pass through. The filtering concept is very powerful and allows us to remove message filtering on the consumer side - being sure all the time that a subscriptions has only specific types of messages.
Unfortunately, there is no support in this moment on Stream Analytics that allow us to set the message properties. When we are sending messages from Stream Analytics to Service Bus, we can specify only the body of the message.
We could find workarounds to it, like using Service Bus Queues or adding an Azure Function between Stream Analytics and Service Bus Topic, that would add the required properties.

Crunch sonar information
This step is done in a similar way as we already done for heating system. The only difference is that in his case we compare the value that is coming from Raspberry PI and compare it with a predefined value.
When we detect that the measured distance is lower than our threshold value we trigger the alarm, by updating a field in Azure Table.
module.exports = function (context, mySbMsg) {
     context.log('Message:', mySbMsg);
    var azure = require('azure-storage');
    var tableSvc = azure.createTableService();
    tableSvc.createTableIfNotExists('systemstatus', function(error, result, response){
                var motiondetectoron = "false";
                if(mySbMsg.avgdistance < 10)
                    motiondetectoron = "true";
                var entityToUpdate = new Object();
                entityToUpdate.PartitionKey= "system";
                entityToUpdate.RowKey = "motiondetectoron";
                entityToUpdate.Status = motiondetectoron;

                tableSvc.insertOrReplaceEntity ('systemstatus', entityToUpdate, function(error, result, response){
                    if(!error) {
                        context.log('motiondetectoron: ', mySbMsg.avgdistance);

Add new functionality in current portal to support Alarms
Similar to heating system, we will use the existing REST API that read data from Azure Table to check if an alarm was triggered. If yes, we will display a custom message on the portal.
    <div @*class="col-md-3" *@>
        <h2>Thief Alarm</h2>
            Alarm status: <b id="thiefAlarmStatus">@(Model.AlarmStatus? "ARMED" : "ACTIVE")</b>
            <img id="thiefAlarm" src="~/images/@(Model.AlarmStatus?"house-alarm.jpg":"house-secure.png")" height="200" />

What to remember

  • There is no support to specify message properties for Azure Service Bus from Azure Stream Analytics


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