using Coax for data transfer

Discussion in 'Computers, Cabling & Other Miscellaneous Hardware' started by lizardking, May 17, 2015.

  1. lizardking

    lizardking IT IS STILL ALL BENS FAULT

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    Hi all Aussiephil has discovered something by using 75ohm coax on 2811 pixels for data and got a run of 70 m from the coax.
    I also ran a test on 2811 just using the center copper wire with the same 75 ohm coax i reached a length of 120 m with 50 pixels so more testing will be needed but there is another option for long runs to the first pixel i do have a corrupt data signal as i have just twisted the wires together cause my soldering iron wont get the coax hot enough to solder but squeezing the wires tight with pliers seemed to work but it alsoit could be the ray wu pixel tester
    https://www.dropbox.com/s/jjoce7nxp74jqav/2015-05-17%2010.51.14.mp4?dl=0
     

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  2. OP
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    lizardking

    lizardking IT IS STILL ALL BENS FAULT

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    Phil can you add to this post please
     
  3. AussiePhil

    AussiePhil Dedicated Elf Administrator

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    OK, some good news and bad news.....


    Good news: this works for 2811 Pixels/strips when driven from the new Falcon F16v2.


    Bad News: Same set up plugged into an ECG-P2 did not work.


    Set up from controller out was
    [​IMG]


    Output connected to 75 Ohm Coax as shown above, 70M of coax, reverse of the above to them connect to 2811 12V strip.


    I will do some more testing with an ECG-P2 but the immediate difference is the buffer driver used for the outputs.
    The ECG-P12R has the same driver so expect the same results.
     
  4. AAH

    AAH I love blinky lights :) Community Project Designer

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    I have no idea why but Ed uses a 300R resistor on the output of the P2 and I assume the P12. I have looked at it on the scope driving into pixels and the signal gets rounded a lot before it even leaves the board. The recommended series resistances that I have seen in pixel specs varies from 30 to 50R so I have no idea why 300R was chosen. I do know that other pixel board manufacturers use a lot lower resistance than 300R and in some cases these resistors can be unplugged and swapped for alternate values.

    They are resistors R51 to R54 at bottom right part of pcb as shown on the P2 pic from the wiki.

    [​IMG]
     
  5. multicast

    multicast Senior Elf Generous Elf

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    Are you sure it wasn't your scope loading the line? What impedance is the scope
     
  6. AAH

    AAH I love blinky lights :) Community Project Designer

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    10M. Can't remember what capacitance the leads are. Genuine Tektronix leads and scope though.
     
  7. #1mate

    #1mate 364 Days building 1 night admiring.

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    AussiePhill,
    Is it necessary to have data input on central core and ground on outer sheath?
    Or was this just a means of extra shielding of data input to enhance range?


    Will be trying to use this on a pix lite 16 (bought 3 before long range pix lite 16 came out :( ) instead of null pixels.
     
  8. AussiePhil

    AussiePhil Dedicated Elf Administrator

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    Essentially yes, Ground must be extended from the controller to pixels and the data should be carried by the centre conductor.
    As the data and clock is encoded together on the single wire and is a square wave the modelling for this electronically is closer to a HF FM transmission.


    All you can do is try, I do however highly recommend getting copper centre and copper shield coax as it makes soldering possible.
     
  9. #1mate

    #1mate 364 Days building 1 night admiring.

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    Thanks,
    Will give it a try next week when i get the right copper coax.
     
  10. barbotte

    barbotte Apprentice Elf

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    hello i am trying understand the concept ,,, where and why would you run a long wire like 30 meter ect ,,, u would still need to run power to it ?? therefore you would need 3 big wire going to your pixel ?? coax and some stp 21 or 2 with at least 14 gage ... is there a smaller controler that can be used closer to your light ?? ... unless it is for roof s ??
    cheer
    good find by the way as it will be good for my roof top
     
  11. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    you can inject power at the end near the lights
     
  12. ShayneT

    ShayneT New Elf

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    Let me first say that my knowledge of electronics is limited. But could Siamese coax like what is used to connect up cameras be used to carry the positive or would that cancel out the benefit of the extra distance achieved by introducing static?
     
  13. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    The issue with carrying the power that distance is voltage drop. The method of sending a signal a long distance either requires the power supply to be at the end next to the lights or else you will need a decent sized guage cable to ensure there is not too much voltage drop at the end of a long run which would be determined by the wire guage used and the load applied
     
  14. ShayneT

    ShayneT New Elf

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    I am hoping on getting 30-40ft without a null pixel.

    How can I tie a power supply at the controller end to play nice or piggyback with one on the pixel end?

    Shayne
     
  15. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    You are only effectivly talking around 12 metres (40ft) in length, so with 12 volts then you could get away with the power at the controller as long as the guage of the cable is sufficient and there is not too much load. If using 5v pixels then you may want the power at the lights, so all you need to do is tie the ground together only and then put the 5vdc straight into the lights from the power supply. Theer are many pictures in the forum and in the ACL 101 lighting manual showing correct power injection techniques
     

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