Help with a data transfer between 2 controllers connected via Azure.

Question

Help with a data transfer between 2 controllers connected via Azure.

Stefan Kraus 0

Hello Community,

This is my first time working with Azure and I'm getting into the IoT topic.

I'm doing a test setup for a customer project where two PLC controllers (Codesys) need to exchange few bits of data.

I get the connection setup of the 2 controllers working, sending data works, though I can't see where the messages end up or where I can view them in the hub.

However, the overview at devices shows me that the messages arrive in the hub.

Through the IoT hub itself, I can also send messages through the device selection in the hub and I receive that message on the PLC and can evaluate it.

However, I don't know how to get the sent message from the 1st PLC to the hub, directly to the second PLC.

My guess lies with the message routing, however, much is still unclear on this.

The test project is first to check the possibility and then at the customer to a paid Azure subscription, for the purpose of message limit to be extended.

Briefly summarized:

IoT Hub in Azure is created, free subscription is active.
both devices are created in the hub
Codesys software is created to the point that both controllers can connect. Both devices can send messages to the hub and the graph in the hub shows the reception.
both devices can also receive messages, which can also be tested via the hub. When the device is selected in the hub and the item message to device is used.

I hope you guys can help me out here and maybe give me some tips on what doc would be most helpful here. Unfortunately Azure is so vast and experience so limited that the docs I've looked through so far haven't really pointed me in the right direction.

Thanks already in advance

LeelaRajeshSayana-MSFT 17,866 Reputation points Moderator

2023-10-25T22:25:13.9866667+00:00

Hi @Stefan Kraus Greetings! I am following up to see if you got a chance to review the below response. Please let us know if you have any additional questions or need further assistance.

If the response helped, please do click Accept Answer and Yes for the answer provided. Doing so would help other community members with similar issue identify the solution. I highly appreciate your contribution to the community.

2 answers

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LeelaRajeshSayana-MSFT 17,866 Reputation points Moderator

2023-10-25T22:25:13.9866667+00:00

Hi @Stefan Kraus Greetings! I am following up to see if you got a chance to review the below response. Please let us know if you have any additional questions or need further assistance.

If the response helped, please do click Accept Answer and Yes for the answer provided. Doing so would help other community members with similar issue identify the solution. I highly appreciate your contribution to the community.

Answer 1

It sounds like you are trying to send data directly from one PLC controller to another through Azure IoT Hub. One way to achieve this is through message routing. You can create a custom endpoint for the second PLC controller and route messages that meet certain criteria to that endpoint.

To set up message routing, you can use the az iot hub routing-endpoint create command to create a custom endpoint that points to the storage container you made in the previous section. Then, use the az iot hub route create command to create a route that passes any message where level=storage to the storage container endpoint.

For more information on how to set up message routing in Azure IoT Hub, you can refer to the following tutorial:

Tutorial: Send device data to Azure Storage using IoT Hub message routing

References:

Answer 2

Hello @Stefan Kraus,

Welcome to this moderated Azure community forum.

You are very busy regarding Azure IoT already. Great!

Regarding the incoming IoT Hub messages sent by devices, these are stored for a limited time on the IoT Hub to be forwarded over either the 'event-hub-compatible-endpoint' or any of the routes or both. Other services like Azure Data Explorer, Azure Function, CosmosDB, blob storage, etc. can receive the messages.

The IoT Hub does not expose the messages directly (for security this is a good decision). You can view the individual messages by consuming them with any of the services or using the VS Code IoT Hub Extension or the Azure IoT Explorer.

The Azure IoT hub does not support device-to-device communication out of the box.

You need to build some custom logic in the cloud that is receiving logic from one device, is making a decision, and sends a command (direct method or device twin desired property change) to the other device.

If you rely heavily on device-to-device communication, check out the new EventGrid support for MQTT (in public preview at this moment).

Here, using MQTT, devices can exchange messages directly where spoofing can be prevented.

Check out this blog post for more details.

Finally, this communication is done between devices via cloud communication.

This makes it vulnerable to network outages.

Why not use a local Edge solution, managed from the cloud? Check out the Azure IoT Edge documentation.

You can use the internal routing for your PLCs to connect them, or you can integrate a local MQTT broker on the edge, managed in the cloud.

If the response helped, do "Accept Answer". If it doesn't work, please let us know the progress. All community members with similar issues will benefit by doing so. Your contribution is highly appreciated.

(this message is written word for word by a real person)

Stefan Kraus 0 Reputation points

2023-10-24T07:06:23.74+00:00

Good morning @Sander van de Velde,

already once a big thanks for the fast answer from you. I have looked at the topic with EventGrid and unfortunately I can't find the solution I need.

It is possible that I have simply overlooked something here, but I do not get a reference to Codesys and the associated library for Azure IoT Hub.

In Codesys, I am unfortunately very limited here and only have the option to send telegrams via http or MQTT and to set the control to receive. I use the MQTT protocol here.

Since here the sending and receiving at least already works and I can confirm that via Azure IoT Explorer already once so far, a custom logic is very helpful here in my case.

Unfortunately, I do not know how to do this most easily in Azure, I lack the experience.

Therefore my further question and for this also already once a big thanks. Do they have here maybe a small example, or tips for the custom logic?

My thought here is that I need to create a storage container in Azure, then transfer the messages that arrive via message routing into the container and only from there is the forwarding then somehow possible. Unfortunately, all the options are overwhelming me and I'm a bit stuck here.

As I said, a big thanks for your help and have a nice day.
Sander van de Velde | MVP 36,971 Reputation points MVP Volunteer Moderator

2023-10-24T10:31:08.21+00:00

Hello @Stefan Kraus,

if you are limited to an MQTT connection only, have a look at this blog post.

There, the MQTT topics are described to communicate with the Azure IoT Hub.

It supports both D2C and C2D communication.

I recommend trying out if you are able to implement DeviceTwin Desired properties support or Direct Method support.

If this works, creating an Azure Function in the cloud is a good investment too:

PLC1 -> IoT Hub -> Azure Function (performing eg. a Direct Method call) -> IoT Hub -> PLC2

Note: the same IoT Hub is written down twice to give it a linear flow.

The logic in the Azure Function (with IoT Hub trigger) can make use of the IoT Hub service SDK. Check the samples for code.

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Help with a data transfer between 2 controllers connected via Azure.

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