Ribbon problems: there has to be a better way!

Discussion in 'General Electronics Chat' started by Steve C, Dec 19, 2008.

  1. Steve C

    Thread Starter Active Member

    Nov 29, 2008
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    So I need several ribbon cable runs. Really easy with IDC connectors, and when completed I had lots of problems with noise all over the place. So I figured I'd use shielded ribbon cable to fix the problem. But I can't find any local source for shielded ribbon cable!

    So I ended up buying some SCSI cable and nipping off the cable heads. Plenty of conductors, I placed them one-by-one into my IDC ribbon heads, and crimped the heads down. so far, so good.

    But the continuity test showed many, many conductors were simply unreliable. the conductors are obviously a little smaller than a standard ribbon cable.

    The next step is to purchase connectors with solder lugs and solder 264 individual little wires! That's not the ideal solution!

    There has to be a connector that will take a wire smaller than a standard ribbon cable, or a way to get the connectors I want without having to make so many teeny solder joints.

    I'm hoping for some advice on what is out there. I typically shop at halted, weirdstuff, excess solutions, and advenced comonent electronics. They've been pretty good at supplying me, but usually it's just the standard IDC connectors and the like, and none have standard shielded ribbon cable.

    Any advice?

    Thanks guys,

    Steve
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Mouser carries Amphenol jacketed and shielded flat cable. It's on page 1032 of teh current catalog. On 1033 there is twisted pair flat cable by Alpha.
     
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    How long is your cable? Is your noise coming from an external source, is it adjacent-wire crosstalk, or is it caused by reflections on a poorly-terminated (impedance) cable?
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    HI Steve:

    Part of the motive for the computer industry going to ribbon cables is/was cost....alas. I had to do a lot of fancy footwork to get my computer equipment to be electromagnetically compatible with my amateur radio equipment...but it IS doable.

    Clamp on Ferrite chokes do wonders....you can get them for ribbon cables. They really are more effective than you'd think. IF the ribbon cables are EXTERNAL to your cabinet, you might need a choke at both ends of the cable.

    There are industrial computer suppliers that make things like shielded ribbon cables, but you pay commensurately.

    How is the noise manifesting itself, by the way? Are you running some kind of instrumentation nearby?

    Eric
     
  5. Steve C

    Thread Starter Active Member

    Nov 29, 2008
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    Automotive environment. Noise is everywhere, and painful to deal with.

    Technically I don't know where the noise is coming from. What I am doing is separating two PCAs that typically reside in a single chassis. No noise. Add the extension cable and pull the boards out of the case, and noise. So everything is now going into individual grounded chassis, and the shielded ribbon.

    I did try the ferrite solution, and it absolutely helped. Major improvement but not 100% solved. I clamped on a ferrite, and there was improvement. So I clamped on another ferrite, and more improvement. Clamped on a third, and it's diminishing retrns, but still improvement. I can't keep clamping on ferrites, so I figured I just needed a shield. The ferrites are now all going on the power input wires (helped there too)

    What I didn't try is a ferrite on each end. Just a bunch together.

    I've got the twisted pair ribbon cable, but my signals arent balanced (carries rs232, audio, digital communication, DC, all sorts of signals) so I wasn't sure how effective that was gonna be.

    I'll check out the mouser catalog for sure. The runs are only about 3-4 feet or so.

    KL7, I'm curious about the methods you employed. care to elaborate?
     
  6. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Interestingly enough, it turned out my major source of broadband H.F. noise was my keyboard! (Going to a laptop solved that problem). The second source was the CRT....I simply tried out a succession of CRTs to find one with adequate shielding. (The screen on my laptop is pretty small, so I like using a separate large display). I 'inherited' an old SUN monitor from work...and it's very clean. These are designed for crucial military and scientific applications. I have no idea what the thing cost new....thank God for DRMO sales. :)

    Another nasty source of noise can be UPS systems. I fixed that source by getting rid of my UPS!

    Merely repositioning cables can sometimes do wonders too. :)

    eric
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    How many signals? If you can go serial data, LVDS through a shielded twisted pair is pretty noise proof - if there is any such thing around a spark ignition.

    I tried some plain copper plug cables once - and had interference on my 8 track speakers.
     
  8. Ron H

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    Apr 14, 2005
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    3-4 feet is too long for fast risetime (<20ns) edges. Reflections could be a problem. You would need slower transition times, source and/or load termination, or shorter cables. You would probably also need to intersperse the signals with ground wires (grounded on both ends).
     
  9. Steve C

    Thread Starter Active Member

    Nov 29, 2008
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    dumb question. Rather than sweat this cable issue, can't I just buy some metal window screening, then cut and wrap my unshielded ribbons?

    Wouldnt that accomplish the exact same thing as buying expensive shielded ribbon? I assume for my application I don't need high conductivity shields
     
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