The MQTT Publish Action Component allows you to publish messages to topics within an MQTT PubSub system.

Here is an example of how to publish messages to a Google Cloud MQTT System:

Navigate to your Google Cloud console and create a project:

Navigate to Google Cloud Platform IoT Core

Enable the Google IoT Core API.

Create a Device Registry

Enter the name of your registry, select the region and add the topics (here events and states for example):

Click on “Add Device” in this screen:

And you will see:

Create a certificate that you can paste into the field by entering this command in your command line:

openssl req -x509 -newkey rsa:2048 -keyout rsa_private.pem -nodes -out rsa_cert.pem -subj "/CN=unused"

This will create a file rsa_private.pem and a file called rsa_cert.pem

Copy the contents of the rsa_cert.pem file into the window:

We’re now ready to take on messages from Gravio.

Note: The MQTT Publish component will take the variables as payload and make one MQTT publish per variable. And if you use JSON or CSV the variable name will be the key/column.

Typically you can use the CreateRecord component to inject a variable into the MQTTPublish component.

(The documentation how to retrieve MQTT messages in Gravio is currently still TBC and being written – please come back in a few days.)

Sending Sensor Data to a MQTT Broker

You can any sensor data to a MQTT broker. In order to do that, you need to fill out the variables into the respective variables using the “Create Record” component. This component will take the sensor data and turns it into output variables, that can be used in the next step with the prefix sin.

This is required because the MQTT component needs input, and you may want to change the naming of the JSON keys. The variables to read initially are prefixed with av (for Action Variable).

The setup looks something like this:

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