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Version: 25.2 (main)

Trigger Messages Using Structured Objects (JSON Objects)

In the previous steps, we learned how to trigger messages by watching numeric variables or setting the bits of a variable. In more advanced scenarios these basic ways of triggering messages can be too limited.

For example:

  • You have a huge amount of possible Message Types.
  • You want the PLC to have control over message metadata like Level, Title, Description, etc.
  • You want to attach additional metadata to messages from your PLC.

In such scenarios, it is the PLC that actually provides the message metadata using a structured object. Let's find out how we can use the trigger called JSON Object to make this all work.

1. What is a Message Object?​

First, let's clarify what Message Objects actually are. Each message is a data structure that can trigger messages and needs to adhere to the following rules:

A Message Object…

  • Can be represented as a string variable that provides all of the message data using a JSON payload.
  • Must contain a Code variable that will actually trigger the message.
  • Can optionally include additional variables that can be be used to define message metadata.
Code (required)
  • Its value represents the Message Code of the message that shall be displayed.
  • Must be of type String. But can of course be used to represent numerical values as well.
  • Signals HELIO to display a message, if the variable is set to a non-empty string e.g. WARN-001
  • Signals HELIO to remove the message, if the variable is set to an empty string again.
  • Should best be called Code, but you can actually call it whatever you like.
Level (optional)
Title (optional)
  • Is displayed by HELIO in the Message Dialog as the title of this message.
  • Must be of type String.
  • Can be a Translation Key. HELIO will translate it automatically.
Description (optional)
  • Is displayed by HELIO in the Message Dialog as the description of this message.
  • Must be of type String.
  • Can be a Translation Key. HELIO will translate it automatically.

Legacy Support: Directory With Child Variables

In previous HELIO versions (25.1 and below), structured objects could be represented as a data directory with message properties as child variables. This is still supported in HELIO 25.2.0 and later versions to support older project configurations without breaking existing projects. For newer projects, use the new Dynamic Message Triggers introduced in HELIO 25.2.0. They allow you to select a variable for each message property instead of specifying a property name, which is a bit more secure since HELIO can verify if this variable still exists.

Outlook: Simplified Message Object Configuration via Structs/Extension Objects

Custom data types and structures, also known as extension objects in OPC UA, will undoubtedly streamline the configuration of such object triggers. We've already started foundational efforts to make this possible in the future. so expect a more simplified setup of message trigger for structured objects in future versions of HELIO.

2. Import Message Objects from Your PLC​

  1. Locate the Examples/Concrete/Messaging/DynamicMessages Variables

Locate the variables and methods in the Data Source Explorer.

You should spot them in this directory:
Examples/Concrete/Messaging/DynamicMessages.

←→
  1. Import Variables & Methods

Let's import the variables and methods into the project so that we can use them in our HMI.

  • First of all import the whole DynamicMessages directory as it contains our dynamic message objects.
  • We're also going to use the two methods SimulateMessage and AcknowledgeAllMessages. So make sure you import those too.
←→

Why Do We Need Those Methods?

Both methods are only needed for simulation purposes:

  • SimulateMessage tells our Playground PLC to fill one of our dynamic objects, so we can simulate a message appearing on our PLC.
  • AcknowledgeAllMessages will cause our Playground PLC to clear all the active messages in the DynamicMessages directory.

3. Setup Your Triggers​

Now that we've got our structured objects, let's define the triggers that will make sure changes to these objects will actually trigger a message.

  1. Define Your First Trigger

Switch to the Message Triggers View, click the Add Type action and choose JSON Message as a trigger type.

  1. Configure the Trigger

The main difference from previous triggers is that we do not hardcode a specific message code for each trigger.

Instead, we will set the Source property of our trigger, which needs to point at our structured object. Select the first message object called Message 0 in the Dynamic Message directory that we imported in the previous steps.

←→

Now, we need to map the properties of the Message 0 object to the fields of our message. Enter the property name Code into the Code Field to instruct HELIO to look into the object and retrieve the message code from the Code property.

←→

When Will Messages Appear?

Once Code changes from an empty to a non-empty string e.g. WARN-001.

  1. Add Additional Triggers

Repeat this procedure for every message object by duplicating the message trigger and simply adjusting the Source property:

←→

4. Create a Page to Trigger Messages​

The excitement is building because we're all set to start sending messages to our HMI. All we need to do is create a small page to simulate the whole thing. Let's get started!

  1. Add a Parameter Page

First things first, we need to create a page. To keep it simple, we're just going to create a basic Parameter Page.

So switch to the Content View and add a Parameter Page.

  1. Turn the Page Into a Component to Add Local State

In order to be able to send multiple Message Codes, we first have to turn the page into a Component (see HELIO Components to learn more about Components).

←→

Define a Component Property named Message Code and add ERROR-1 and INFO-1 as possible values. This will allow us to send these values to the PLC.

  1. Add a Magic Input to Control the Message Code.
  • Add a Magic Input to control the Message Code that shall get sent to the PLC and set its value property to the Component Property that we've just defined.
  • Add a Button to call the SimulateMessage method.
←→

5. Simulate Our First Messages​

Let's Get Those Messages Fired Up!

  • Switch to PLC Mode to make sure you will be writing to the actual PLC.
  • Switch to Test Mode so you can toggle the inputs.
  • Click on the button to simulate messages.

Your HMI should behave something like this:

6. Map More Object Metadata​

So far HELIO only receives the Code from the PLC. But we can provide more message metadata from the PLC.

  1. Map More Message Fields

Go back to your trigger definition and make sure all of the object's properties will get mapped from the PLC to the fields of the message:

  • Locate the Mapping section.
  • For each field of the message (Title, Description, …) enter the name of the structured object property that will provide the metadata.

Once this is done, your trigger configuration should look like this:

7. Removing Messages​

Now that we have messages in our Active Messages list, we need to ask ourselves how those messages will become inactive. How are messages resolved and moved into the Message Archive?

When Will Messages Disppear?

Once the Code changes back from a non-empty string e.g. WARN-001 to an empty string.

So the PLC is able to remove messages from the list by resetting the Code property of the object to an empty string. Once this is detected, HELIO will mark this message as archived.

In real life, this might be caused by:

  • The actual error or situation that caused the error has been resolved, so the message can be archived.
  • There is an additional hardware button to acknowledge all messages which can be pressed by operators. This hardware acknowledgement will be used by the PLC to reset all the message objects and set their Code attribute to an empty string.

For our simple test HMI:

We will simulate this process by calling the AcknowledgeAllMessages method. This resets all objects in the DynamicMessages directory and sets their Code attribute to an empty string.

  1. Add a Header Cell

Let's add a simple Header Cell to trigger the method:

  • Add it to the header of your HMI.
  • Set its Title to Clear Messages.
  • Choose a nice Icon that gets the message across, e.g. Broom.
  1. Configure On click Property

Activate the On click property and choose the Call Data Method Action as its type:

←→
  1. Clear Some Messages

Switch to test mode and click Clear Messages. Any active messages that you triggered before should no longer appear.

Mission accomplished!

You've learned how to trigger and archive messages using structured objects.

However, there is another way! So, if you're interested in triggering dynamic messages using property variables, stick around for the next guide.