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Thread: DMX... Timing issue?

  1. #1

    DMX... Timing issue?

    Hi all

    I am using TeensyDMX.h on a 4.1, with a CTC-DRA-01-R2 DMX shield.

    Daisy chain of 8x DMX lights on the system, and they all work fine... except two lights of a particular type.
    These two don't play ball and flicker a lot. Either with or without a termination resistor in place.

    Channel 0 is dimming/brightness level(0-255)
    1, 2 and 3 are the RGB colours.

    I am using the simple dmxTx.set(1, 0); command to control the required channel.

    Any ideas what I can try to fix this issue? There seem to be a lot of extra commands in the keywords list, but I have no idea what any of them do.
    I was thinking it might be a timing issue?

    #######################################
    # Syntax Coloring Map for TeensyDMX
    #######################################

    #######################################
    # Datatypes (KEYWORD1)
    #######################################

    Receiver KEYWORD1
    Sender KEYWORD1
    Responder KEYWORD1
    PacketStats KEYWORD1
    ErrorStats KEYWORD1

    #######################################
    # Methods and Functions (KEYWORD2)
    #######################################

    begin KEYWORD2
    end KEYWORD2
    packetCount KEYWORD2
    setTXEnabled KEYWORD2
    setKeepShortPackets KEYWORD2
    isKeepShortPackets KEYWORD2
    readPacket KEYWORD2
    get KEYWORD2
    get16Bit KEYWORD2
    packetStats KEYWORD2
    lastPacketTimestamp KEYWORD2
    setResponder KEYWORD2
    setSetTXNotRXFunc KEYWORD2
    setRXWatchPin KEYWORD2
    rxWatchPin KEYWORD2
    connected KEYWORD2
    onConnectChange KEYWORD2
    errorStats KEYWORD2
    setBreakTime KEYWORD2
    breakTime KEYWORD2
    setMABTime KEYWORD2
    mabTime KEYWORD2
    setBreakSerialParams KEYWORD2
    breakSerialBaud KEYWORD2
    breakSerialFormat KEYWORD2
    setBreakUseTimerNotSerial KEYWORD2
    isBreakUseTimerNotSerial KEYWORD2
    setPacketSize KEYWORD2
    packetSize KEYWORD2
    set KEYWORD2
    set16Bit KEYWORD2
    clear KEYWORD2
    fill KEYWORD2
    setRefreshRate KEYWORD2
    refreshRate KEYWORD2
    pause KEYWORD2
    isPaused KEYWORD2
    resume KEYWORD2
    resumeFor KEYWORD2
    resumedRemaining KEYWORD2
    isTransmitting KEYWORD2
    onDoneTransmitting KEYWORD2
    outputBufferSize KEYWORD2
    isSendBreakForLastPacket KEYWORD2
    preBreakDelay KEYWORD2
    preNoBreakDelay KEYWORD2
    preDataDelay KEYWORD2
    eatPacket KEYWORD2
    processByte KEYWORD2
    receivePacket KEYWORD2

    #######################################
    # Instances (KEYWORD2)
    #######################################

    #######################################
    # Constants (LITERAL1)
    #######################################

    kMaxDMXPacketSize LITERAL1
    kMinDMXPacketSize LITERAL1
    kMinTXBreakTime LITERAL1
    kMinTXMABTime LITERAL1


    Thanks

  2. #2
    Hmm I am starting to think this is something to do with the entire TeensyDMX library.

    We used DMXsimple on another project and it worked fine. But DMXsimple doesn't compile on a 4.1, it throws up an error

  3. #3
    Putting this in fixes the issue..

    dmxTx.setPacketSize(100);
    dmxTx.setRefreshRate(40);

    What the heck in means, who knows.

    I just don't understand why they bother to give you a text list of Keywords, and no explanation of what the hell they do. Not everyone knows this stuff.

  4. #4
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    Quote Originally Posted by SteveCS View Post
    Putting this in fixes the issue..

    dmxTx.setPacketSize(100);
    dmxTx.setRefreshRate(40);

    What the heck in means, who knows.

    I just don't understand why they bother to give you a text list of Keywords, and no explanation of what the hell they do. Not everyone knows this stuff.
    @SteveCS:

    Seems that you may not have read the README for the library ??

    The following excerpts are taken directly from the README.md file:

    ### Packet size

    The packet size can be adjusted and retrieved via `setPacketSize` and
    `packetSize()`. Smaller packets will naturally result in a higher
    refresh rate.

    This can be changed at any time.
    And

    ### Transmission rate

    The transmission rate can be changed from a maximum of about 44Hz down to as low
    as you wish. See the `setRefreshRate` and `refreshRate()` in `Sender`.

    Note that the rate won't be higher than the limits dictated by the protocol,
    about 44Hz, no matter how high it's set. The default is, in fact, `INFINITY`.

    This can be changed at any time.
    As referenced in the README.md file, the following code excerpt is taken directly from Sender.cpp:

    Code:
    bool Sender::setRefreshRate(float rate) {
      if ((rate != rate) || rate < 0.0f) {  // NaN or negative
        return false;
      }
      if (rate == 0.0f) {
        breakToBreakTime_ = UINT32_MAX;
      } else {
        if (refreshRate_ == 0.0f) {
          end();
          begin();
        }
        breakToBreakTime_ = 1000000 / rate;
      }
      refreshRate_ = rate;
      return true;
    }
    The author of that particular library is very active in this forum. A polite inquiry would probably elicit an informative reply.

    Hope that helps.

    Mark J Culross
    KD5RXT

    P.S. I have absolutely no experience with DMX, nor with the TeensyDMX library, but I am very comfortable digging thru code to try & analyze/understand underlying functionality, so I thought I'd take a look to see if I could possibly provide any assistance. I do hope that helps. MJC

  5. #5
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    Quote Originally Posted by SteveCS View Post
    Hmm I am starting to think this is something to do with the entire TeensyDMX library.

    We used DMXsimple on another project and it worked fine. But DMXsimple doesn't compile on a 4.1, it throws up an error
    @SteveCS:

    I do not have any experience with DMX in any form, but in an attempt to possibly provide some help, I loaded up the TeenxyDMX library.

    I tried compiling both of the examples for DMXsimple, & they both successfully compile with the following setup:

    Code:
      Arduino IDE Configuration (last built with Arduino 1.8.19 + Teensyduino 1.58b2):
         Tools/Board:           "Teensy 4.1"
         Tools/USB Type:        "Serial"
         Tools/CPU Speed:       "600MHz"
         Tools/Optimize:        "Faster"
         Tools/Keyboard Layout: "US English"
         Tools/Port:            "COMx Serial (Teensy 4.1)"
    Post the full text of the error (this is a variation on the "Forum Rule: at the top of the page") that you are encountering for potential help in resolving that.

    Mark J Culross
    KD5RXT

  6. #6
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    The keywords.txt file is for the Arduino IDEís syntax colouring. Itís not meant as documentation. Iíve tried to make the README as complete as possible, but perhaps it deserves a section on possible electrical or ďbad hardwareĒ problems. (I canít promise a timeline for adding it, however.)

    The issues you describe might be electrical, or they might be due to the fixture not completely following the DMX spec. If you got it to work by changing the refresh rate, then maybe thereís something wrong with the lights, or even cabling. How are you connecting everything? What sort of cables are you using? For example, how long are they and what is the impedance? A common mistake is to use microphone cabling instead of DMX cabling; those have different characteristic impedances.

    Flickering can also happen when a fixture receives non-null-start-code data and it doesnít ignore those packets. Or maybe those lights just canít handle a 44Hz refresh rate. Does changing the refresh rate without changing the packet size work too?

    Or maybe the daisy chained devices are somehow interfering with the signal? What happens if you just connect the lights that flicker, without daisy chaining them?

    Could you post your code? (Please wrap in CODE tags if you paste code.)

    Iíve spent a lot of time verifying the library produces DMX signals that are accurate and correct, and while that doesnít guarantee anything, Iíve been using this library in real-world projects with success. Problems that Iíve seen are most frequently with the fixtures themselves not being implemented properly or with how everything is hooked up, and with what components and wiring.

    @SteveCS, What does the output look like on a scope or logic analyzer? TeensyDMX is interrupt-based and asynchronous, and so itís possible that other libraries interfere with the timing, however, I wouldnít expect, because of the flexibility in the DMX protocol, that the signal would be changed bad enough to go out of spec.

    (Thanks, @kd5rxt-mark, for jumping in.)
    Last edited by shawn; 12-19-2022 at 04:18 PM.

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