DCC issue with Heljan Turntable

Discussion in 'DCC Control' started by Brian A, Jul 2, 2020.

  1. Jim Freight

    Jim Freight Full Member

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    Hi Brian

    My opinion at this stage from what you have described and the YouTube video is as follows.

    It is very likely that the TT bridge motor is a stepper motor and is told to step a number of times in a particular direction by the control panel.
    The control panel holds the user data on where each entry/exit track position is relative to the zero datum as a number of steps.

    The TT bridge PCB would have no knowledge of where the entry/exit tracks are.

    I see no evidence that the TT well, pit or bridge incorporates any absolute position feedback, also it would cost too much for a £200 TT.

    The only feedback that appears to be fitted is the IR emitter in the well side used to zero datum the motor controller in the TT bridge.

    Every other movement is open loop and relies on the stepper motor not missing a step. For example if the bridge was to jam for a few steps it would stay out of alignment with the tracks until the the IR emitter was passed again. Small missteps would be accommodated by the chamfered track ends on the TT bridge and the entry/exit tracks.

    The Tx/Rx interface between the control panel is a possibility, electrical interference, connector at the TT PCB or an interface component on the TT PCB but this would not explain how the track number on the control panel is correct without feedback from the TT PCB, which as I believe from above it cannot provide.

    Given that the DCC sniffer detects no rogue commands and the track# on the control panel matches the TT position my next point of investigation would be to apply a digital scope to analyse the Tx/Rx connection between the control panel and the TT bridge and decode the communications which I would expect are simple in format.

    Quite a mystery, I would be interested to know what the issue turns out to be when you solve it.

    Jim
     
  2. Brian A

    Brian A Full Member

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    Jim,

    Good synopsis, however not quite correct. From the MERG article and my own physical inspection, all the logic is on the PCB in the bridge. There is a chopper in the bridge which is what it uses for tracking its position. The IR is only used to give a reference point for the bridge to know its start position.

    If you change the control box, the bridge retains the knowledge of the positions of the tracks. I believe all the control box does is manage the user controls, update the display, change the voltage and read the DCC commands/user input and send them to the Bridge.

    The MERG article in December 2018 edition has put a digital scope and has deciphered a lot of the messages. He then used an Arduino to interface it with the MERG CANBus. I was considering doing something similar with an Arduino to filter the DCC commands, but its a bit above my skill level. Not sure that would fix the problem either.

    I also thought the interference could be on the cable, so I wrapped it in foil.

    Ill keep scratching.

    Brian
     
  3. Jim Freight

    Jim Freight Full Member

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    Hi Brian
    Right, I stand, or rather, sit corrected :avatar:

    What is a 'chopper' in the context of this TT?
    All this seems a lot of work, oh, and don't forget to enjoy your trains, I forget occasionally :facepalm:

    Jim
     
  4. Brian A

    Brian A Full Member

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    Jim, thanks for your inputs, you have got me to try some different things, no joy thou :-(

    The chopper is like a small propellor that the motor drives, the blades cut a beam and the PCB uses that to track the movement of the TT.

    To install and setup the TT was pretty easy and it works really well EXCEPT for these bloody unannounced movements. Apart from that I am enjoying my trains, have two layouts and currently building a garden railway.

    Cheers
    Brian
     
  5. Jim Freight

    Jim Freight Full Member

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    Right Brian, as fitted to early optical computer mice.

    What scale and standards are you building your garden railway to?

    Jim
     
  6. Brian A

    Brian A Full Member

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    Jim Freight likes this.
  7. Jim Freight

    Jim Freight Full Member

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  8. Geoff-Lousy

    Geoff-Lousy Full Member

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    Hi Brian,
    I have the same issue with RR@co and my Walthers (Heljan) turntable (- weird random movements). I was just wondering if you ever found the cause of the problem and/or a solution?
    Cheers.
    Geoff
     
  9. Brian A

    Brian A Full Member

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    Geoff,

    No I haven't been able to fix the problem. Currently I have no further avenues of investigation. I have proven that it is internal to the blue box, but what causes it I haven't been able to establish.

    I am moving my RR&Co onto a O gauge garden railway and turning my OO into an On30 layout. The heljan TT will be used on the On30 layout but I will wire it up with 13-16VAC for TT operation and DCC only to the tracks.

    Cheers
    Brian
     
    jakesdad13 likes this.
  10. M Reed

    M Reed Full Member

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    Dear "Brian A",

    I joined this forum specifically to add to your extensive and detailed post about DCC problems with your Heljan 89121 turntable. I also have this model (in fact 2 - 1 as a spare as the first one blew up with the usual Err1 power issue), it also suddenly produces random movements and I have also gone through many of the same tests that you have. I run a Digitrax DCC setup and like you, use Railroad & Co.'s Traincontroller software (V8 Gold). I agree that these random movements at any time in an operating session ruin any chance of properly using the TT with Traincontroller, schedules, Autotrain etc. because half the time the TT is unlikely to be where TC was last told it was. As you say - "engine in pit" is the usual result!

    There is one important diagnostic that you could check although I appreciate that you may no longer be using your #89121 with DCC - partly because of this seemingly intractable issue. I first read about this on an RMWEB post by "westaust55", who posted this discovery back in 2017.

    Using the default base address of 57, my first DCC Track 1 address is accessed using ID=225, 'closed' or 'thrown'. My registered Track 2 address would therefore be 226, Track 3 = 227, and so on. I have 12 tracks orientated in pairs, so my twelfth and final position would be accessed using ID= 236. As for you, all this works fine with the Heljan's blue controller, calling Go/Set 1-12, or DCC "points" 225-236, or calling 225-236 'c' or 't' in TC's macros, push-button actions etc.

    However, if I ADD 256 to these numbers, I get the same movements - as suggested by "westaust55". So, if I call, say, 227+256 = 483, the TT will ALSO move to Track 3. If I add another multiple of 256, so (228 (Track 4) + 2*256) = 740, the Heljan TT will move to Track 4 !! If I add 3*256 to my actual track IDs, I will get the same movements. I haven't tested it beyond ID=999, but the sequence of erroneous moves may well be infinite.

    You could test this theory of adding one or more multiples of 256 to your range of TT DCC track position addresses and see if you get the same movements. To my mind this explains the seemingly random and uncalled-for Turntable movements. In my case, my actual points number 1 to 124, my TT should be restricted to the low 200's - where absolutely nothing else is used, but above about 400, I have several Digitrax SE8c boards which are switching signals. So, the switch of some signal on the other side of the layout from amber to green may call ID 742, and that will ALSO cause the Heljan #89121 to move to Track 5 - and so on. There is no range of accessible Heljan Turntable base addresses that, when multiples of 256 are added, do not result in conflict with signal boards etc. on my layout.

    So, your observation that the DCC sniffer showed no untoward calls in the desired TT address range is correct - I found the same thing. In your conversation, the suggestion that one might use an Arduino interface to limit/filter the addresses that the TT controller sees is an excellent one, but is also a bit above my skill level. You use a Lenz DCC system, I'm using Digitrax, and 'Westaust55' was using NCE, so this is nothing to do with Command Station models or manufacturers.

    It is quite simply, a big bug in the address handling firmware in the Heljan blue control box. When contacted by both you and Westaust55, they seemed to prevaricate or blame other vendors' equipment. I have now written to them too and even sent them the pictures they requested etc. If you can reproduce this specific behaviour of wrongly also interpreting/acting upon your correct addresses + multiples of 256, then the bug will be very well confirmed.

    I hope that this has been interesting or helpful for you - please let me know what you think.

    Martin Reed
     
  11. Brian A

    Brian A Full Member

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    Martin,

    Thanks for posting your findings, I still run my Heljan TT on DCC but I only use it with TC when I am not running trains etc, just doing shunting.

    I am away until the end of the month, but I will do the test as soon as I am back. I will let you know the results.

    I do have my spreadsheet with the point and signal allocations so I can look to see if I have numbers in the +256 range.

    Cheers

    Brian
     
  12. Brian A

    Brian A Full Member

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    Martin,

    I looked at my spreadsheet and because of the problem I set my TT to 60 = DCC addresses 237-262. I then reprogrammed all my signals and points (Over 100 of them) to be less than 237. So the +256 bug isn’t causing my movements.

    Once I changed to the above scenario the number of random movements reduced significantly. I still get movements but like 3-4 an operating session rather than almost constant movement I was getting earlier.

    This does however give me something to work on. I suspect that there may be another number that may be causing issues. As 256 is a significant number in binary maybe a lower number may also be causing the problems. It may be a binary interpretation issue.

    I will test the +256 bug when I get home and do some more testing to see if I can get to the bottom of the issue.

    Cheers

    Brian
     
  13. Brian A

    Brian A Full Member

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    So I tried something different today. I got my mate, who is pet sitting for us, to boot up the trains and test the TT. I had to walk him though using the Lenz hand controller over the phone.

    Results were the +256, and +512 bug were confirmed. Ie with Heljan accessory address set to 60, DCC addresses 243, 499 and 755 all moved the TT to track 7. 256 and 512 are the next two binary digits above the DCC address ie 243 = 11110011, 499 = 111110011 and 755 = 1111110011.

    What these means is that Heljan are only reading the first 8 binary digits of the address. Which explains why they limit the accessory address to 60.

    Still doesn’t explain why mine still does unexpected movements with all my accessory addresses below the TT addresses. I need to do some more sniffing. The issue is that there is normally about 2-3 commands around when the TT movement starts. But with this new knowledge I may be able to see what code is causing the movement.

    I will do some more testing when I get home.

    Cheers

    Brian
     
  14. M Reed

    M Reed Full Member

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    Dear Brian (and your Pet-sitting mate!),

    Your confirmation is excellent news and really explains not only what the Heljan blue control box is doing, but also what they need to do to fix this bug. I agree that there may be higher addresses (i.e. above the last Heljan registered track DCC ID) that are being called or switched that I'm not aware of. On my system, all the Digitrax boards also support "Routes" which may well involve these higher IDs. I never use these Digitrax routes and leave all of that to TC, but that doesn't mean that some of these IDs aren't being changed/called as points or signals are switched.

    I too can do some more tests and 'sniffing', and am happy to report back on this forum. However, I feel that with your detailed contribution, Heljan now have plenty to work with - basically if they read the whole address in binary, rather than just the first 8 digits, the problem should go away and the resultant turntable action would be restricted to only exactly the registered addresses desired and called.

    Thank you for your contribution to this. Heljan haven't got back to me with a course of action yet, but I can send them a synopsis of this confirmation too.

    Cheers
    Martin
     
  15. M Reed

    M Reed Full Member

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    Dear Brian (again),

    I briefly tested the theory that other 'significant' binary numbers could also cause extraneous movements, but I only get the unwanted turntable moves with multiples of 256 added. Here are my quick results, as far as they go (using Base Address = 57 as before) :-

    Correct/desired address Track 03 Track 04 Action
    227 228 Turntable moves Trk 3 <-> 4 desired movement
    add 256 to these No. 483 484 Turntable moves Trk 3 <-> 4 unwanted movement.
    add 128 to these No. 355 356 No movement
    add 64 to these No. 291 292 No movement
    add 256 + 32 to these No. 515 516 No movement
    add 256 + 128 to these 616 612 No movement
    add 256 + 256 to these 739 740 Turntable moves Trk 3 <-> 4 unwanted movement.

    Like you, I'll still try and understand exactly what is calling or changing these higher IDs on my layout - i.e. (in my case) Digitrax's unused "Routes" or something else.

    Cheers
    Martin
     

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