kwaltzer (Customer) asked a question.

March 7, 2024 at 5:49 PM
MQTT set up help

I have watched a few videos regarding the MQTT functions. We will be using the Node Red and Mosquitto broker for the data handling and directory to server.

My questions though are pertaining to the packing and unpacking of data to send via the MQTT. I need to send the follow points:

Send out / publish:

Cycle Count (integer)

4 different Temps (all integers)

Mold# (integer)

Material Type (string)

Downtime Category (integer)

Downtime start and end (integer)

Downtime description (string)

4 cycle times (all integers)

Notification to print part bin tag (0=no print 1=print unless i can figure out how to print from the serial com module with a QR code)

Receive / subscribe:

Use server as a data base for recipes

When mold number is entered or QR code is scanned, would load recipe parameters

mold# (integer)

material type (string)

2 cycle times (integers)

4 temps ( integers )

 

I need to make sure im thinking about it the right way from what I have seen. I will need to use the pack string instruction to create a payload for the broker topic, correct?

Some of the information will be sent at different times. For instance I will need the cycle count and cycle times to be sent at the end of every cycle, but downtime can be sent over only when there is downtime. Under the publisher parameters there is an enable and a publish rate. If i need data to be sent on a triggered basis, I will need to have the trigger the enable for that publisher and make the publish rate long so it only sends once while the enable is triggered?

 

When subscribing to a message I will need to use the unpack string, and or extract string to separate out the specific data integers or strings then assign them to there proper locations, correct?

  • 18 answers
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  • Durallymax (Customer)

    The tag names will not be part of the payload, you'll specify the key names and use the tags as the values.

     

    A PKS would look like this

    "{"mold":" | 8

    MoldTag | 4

    ","count":" | 9

    CountTag | 5

    "}" | 1

     

    Note, additional quotes are shown as needed for Psuite literal strings. Fixed values are shown for lengths, use SLEN for strings of variable length and use the integer it returns in place of fixed length.

     

    Don't forget to set the precision on Floats/Reals and remember the decimal itself counts as one char when setting the length (and some brokers are picky when there is not a number after a decimal).

     

    You can add as many variables to a payload as practical, separate the key/value pairs with a comma. You can use multiple PKS to make a single payload if your data is concise and you haven't hit Psuite's 128char limit. You may find value in adding some data as context instead also, quite a few options you can explore on the web.

     

    If you need to publish more than will fit into a 128char string, break it up into multiples. In your MQTT Setup, create a 2D array of 128char strings. MQTTPubPay(1),(1) is payload 1 for publisher 1. MQTTPubPay(3),(10) is payload 10 for publisher 10. Just an example, name as you see fit. You can publish up to 10, 128char strings at a time for each publisher. If you need to publish more than this, write your own queueing routine to build strings, publish them and then build the next set and publish. Etc.

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  • Durallymax (Customer)

    You're on the right track.

    Use PKS and SLEN to build your strings. Create an array in the MQTT config if you need more than a single 128char string sent at a time.

    You can use the polling rates inside the config but these aren't(or at least weren't) adjustable with a runtime transfer. Instead I just queue it all outside and build different strings at different times. I'll use all of the publishers at times, but set them all to zero and trigger at whatever rate is needed in the Ladder.

     

    You'll need to use Extract String to find the topic you're looking for then unpack to get the data out.

     

     

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    • kwaltzer (Customer)

      Thanks for your input.

      I will need to use the String Length Function (SLEN) for only the data points that maybe variable in length correct? Ex. Mold# could be 9801 or 16605.2

      Each payload per topic has a max of 128 characters? So if the payload is over that limit, I will have to add another topic for the rest of the info? The data that is packed into the payload looks like it wont have the tag names associated with it. If I want to add a name identifying each piece of data, (ex. count-XX, top heat- XXX, scrap-XX, etc) do I have to create each on with its own packed string function, and pack those new strings into the payload?

       

       

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      • Durallymax (Customer)

        The tag names will not be part of the payload, you'll specify the key names and use the tags as the values.

         

        A PKS would look like this

        "{"mold":" | 8

        MoldTag | 4

        ","count":" | 9

        CountTag | 5

        "}" | 1

         

        Note, additional quotes are shown as needed for Psuite literal strings. Fixed values are shown for lengths, use SLEN for strings of variable length and use the integer it returns in place of fixed length.

         

        Don't forget to set the precision on Floats/Reals and remember the decimal itself counts as one char when setting the length (and some brokers are picky when there is not a number after a decimal).

         

        You can add as many variables to a payload as practical, separate the key/value pairs with a comma. You can use multiple PKS to make a single payload if your data is concise and you haven't hit Psuite's 128char limit. You may find value in adding some data as context instead also, quite a few options you can explore on the web.

         

        If you need to publish more than will fit into a 128char string, break it up into multiples. In your MQTT Setup, create a 2D array of 128char strings. MQTTPubPay(1),(1) is payload 1 for publisher 1. MQTTPubPay(3),(10) is payload 10 for publisher 10. Just an example, name as you see fit. You can publish up to 10, 128char strings at a time for each publisher. If you need to publish more than this, write your own queueing routine to build strings, publish them and then build the next set and publish. Etc.

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      • kwaltzer (Customer)

        Awesome, got that part straight then.

        One last thing for now, the integers that may vary in length. Since they are not strings, I cant use the string length instruction to determine their length. Will i need to use the copy data instruction to move the data point from an integer to a string tag, then use the string length instruction to determine the length?

      • Durallymax (Customer)

        That would probably be the easiest way to do it. I usually just set ints/floats to the max length I expect. Your payload string will need to be large enough to accommodate them at their largest anyway and the whitespace doesn't impact MQTT.

      • kewakl (Customer)

        It would be nice if 'Log(n)' result to an int were truncated and not rounded. We could size an int tag using Log() + 1.

         

        Log(n) discrepancy

  • kwaltzer (Customer)

    Hey everyone. Made my way back to this project with some progress so bare with me. I am using Node-Red which is running on our Linux server where the SQL database is stored. Here is some examples of a test program I have done so far.

  • kwaltzer (Customer)

    This is 1 of 3 pack string instructions to pack the payload for the MQTT. There are 3 Publish Payloads in total.

    Since there is only a certain amount of lines in the pack string and commas are needed so the SQL database knows what data point to put in its respected column, i needed to have three separate payloads.

    • payload prop

    • Durallymax (Customer)

      Tip if you want to make a bigger string, are not at the 128char limit and run out of lines.

      Build the first part of your string into "Pub_Payload" in a PKS. In a rung after that PKS create an SLEN for "Pub_Payload". Create a second PKS in the next rung and the first line will be "Pub_Payload" as the string and the SLEN result. Repeat as necessary.

       

      Just make sure you aren't sending this string until after it is fully built, or use a buffer tag for the intermediate steps if worried about sending a partially built payload inadvertently.

       

      Also make sure your variable length elements will not tally up to exceed the 128char limit in Psuite.

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      • kwaltzer (Customer)

        That actually worked out really well. Thanks!

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