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  • Shielding materials

    Hey guys...

    Due to the weak VGA connector on this mainboard, I decided that I would wire a VGA plug to a bigger plug that you can see on the left side instead of having the VGA plug hanging from the connector. Since my Xenarc only uses 7 pins from the VGA cable, I can get away with using just those.

    I tested it out and it works fine, but there is a slight bit of ghosting on the image, and dark, scrolling horizontal bands appear when I use the mouse or the computer accesses the HDD. As soon as the HDD activity stopps, they disappear.

    Now I should point out that the USB lines are also in the same big white connector. I am mounting them in there due to space concerns. When I disconnected the USB from the mainboard, the video anomolies remained.

    Now, my question is, what can I use to shield the VGA cables? I see that in a standard monitor cable there is a foil like material wrapping the wires, is that something I could use to reduce the interferrance?

    Thanks!


  • #2
    bump?

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    • #3
      You could try using Ferrite Cores on the VGA cable, don't know how well they work. Mine will be here in a couple days I'll find out then.

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      • #4
        Bumpski!

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        • #5
          Try wrapping it in aluminum foil and grounding the foil. Wrap tape around the whole thing to prevent your foil from tearing when your cable is bent. Ferrite cores could be used as well.

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          • #6
            Just commenting. That's one tiny computer! Nano board? Got a write up?
            Good luck with the VGA prob.

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            • #7
              Tried foil.. no cure.

              I also replaced the unshielded wire with the same stuff that a proper VGA cable is made of, with the foil liner, grounded the ends, etc... nothing seems to offer any improvement

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              • #8
                Originally posted by guizai View Post
                Just commenting. That's one tiny computer! Nano board? Got a write up?
                Good luck with the VGA prob.
                Advantech PCM 9731 3.5" single board computer.. similar HxWxD size as a desktop computer hard drive.

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                • #9
                  Sometimes, arranging the cables properly will make the most difference. Remember if you want to reduce interference between two cables, its best to have them intersect at 90 degree angles (although thats usually hard to do). I cant really give you a guide on how to arrange your cables...but maybe use a little common sense, and look at ways you can arrange them differently.
                  Have you tried powering your computer at home and seeing if there is interference? It seems to me that the emf in your vga signal might also be passed on from within the circuit board itself, so there may be little (if at all), that you can do. If you are desperate to try anything,you could add ferrite cores to as many of your cable ends as you can, although I doubt you will notice a difference.

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                  • #10
                    It is doing it on my workbench, haven't put it in the car yet.

                    The cable itself that runs under the motherboard is shielded, and I have even tried it witht he cable extended perpendicular to the long edge of the motherboard, all with no change.

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                    • #11
                      Perhaps you've created a ground loop. I'm guessing you have a ground path through the VGA cable and another through the power supply that powers your monitor.

                      If you have a big pickup loop, then no amount of shielding will help, only breaking the loop. Tell us as much as you can about the monitor power supply and the PC power source -- do they share the same power supply, is the ground for the monitor through the VGA cable assembly?

                      If they share a common ground through 2 different paths, then you could try eliminating one of the two grounds or adding a ferrite bead in series with one of the grounds to choke off high frequency current. You can also try a capacitor from shield ground to digital ground at the monitor end of the cable to act as an AC short. Probably a 10nF capacitor with short lead length will be most effective (depending on frequencies present).

                      Switching power supplies put out a lot of EMF that can interfere with signals. Make sure your cable assembly is routed clear of power supplies, specifically the inductors. Usually a few inches is enough distance to get out of the big near-field stuff.

                      If you don't mind having the computer end hardwired, you could also remove the VGA connector and solder a regular VGA cable where the VGA connector goes.

                      I'm guessing you've attached a regular monitor to the VGA connector and the picture is perfectly clear so we aren't trying to troubleshoot a "feature" of the motherboard?

                      Good luck,
                      Mark Stubbs
                      http://www.bibaja.com

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                      • #12
                        are you shielding each wire individually?
                        try that
                        don't share connectors
                        even proper cables have enough troubles

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                        • #13
                          Originally posted by bibaja_llc View Post
                          Perhaps you've created a ground loop. I'm guessing you have a ground path through the VGA cable and another through the power supply that powers your monitor.

                          If you have a big pickup loop, then no amount of shielding will help, only breaking the loop. Tell us as much as you can about the monitor power supply and the PC power source -- do they share the same power supply, is the ground for the monitor through the VGA cable assembly?
                          Current test bench setup: Standard desktop computer whos power supply I have tapped into for 5 and 12 volts for the carputer.

                          I have tried this using two monitors. One being my Xenarc (powered by the same power supply as the one running the carputer) and a standard desktop LCD monitor.


                          Originally posted by bibaja_llc View Post
                          If they share a common ground through 2 different paths, then you could try eliminating one of the two grounds or adding a ferrite bead in series with one of the grounds to choke off high frequency current. You can also try a capacitor from shield ground to digital ground at the monitor end of the cable to act as an AC short. Probably a 10nF capacitor with short lead length will be most effective (depending on frequencies present).

                          Switching power supplies put out a lot of EMF that can interfere with signals. Make sure your cable assembly is routed clear of power supplies, specifically the inductors. Usually a few inches is enough distance to get out of the big near-field stuff.

                          If you don't mind having the computer end hardwired, you could also remove the VGA connector and solder a regular VGA cable where the VGA connector goes.

                          I'm guessing you've attached a regular monitor to the VGA connector and the picture is perfectly clear so we aren't trying to troubleshoot a "feature" of the motherboard?
                          Using a standard VGA cable between the carputer and the desktop and Xenarc LCD's results in a perfect image. I'd rather not remove the VGA connector from the motherboard and solder directly to it as I am not sure where I am getting an interferance leak.

                          One thing to note is that the image is fine with no PC activity. When the hard drive is in use, or I move the mouse around, then I get the flickering on the screen, leading me to believe that it isn't a grounding issue and more of a EMI issue.

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                          • #14
                            Originally posted by davesaudio2 View Post
                            are you shielding each wire individually?
                            try that
                            don't share connectors
                            even proper cables have enough troubles

                            I can't possibly shield each wire indivually, besides, the VGA cable doesn't do that anyway, I think it would be a waste of time.

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                            • #15
                              In one quick swoop, I have simultaneously ruled out everything I thought it could have been.

                              Since I am using that big white connector for both VGA and USB, I thought maybe the USB cables were causing some interference. Unplugged the USB plug from the mainboard, the problem was still there. Ok, maybe the USB lines that run under the mainboard are picking up some noise...

                              Anyway, I finally had the bright idea to take the VGA plug that plugs into the motherboard and connect it to the back of my laptop. Image was as solid as it ever should be.

                              So, the white connector isn't allowing anything to get in, it isn't poor shielding on the USB line, it isn't poor shielding on the VGA plug or a bad soldering job somewhere... (Yes, I had the small board running while I tested this to see if any noise could be leaking into the VGA line somehow...)

                              So.. the only time when I get the interference is when the monitor (either monitor) is plugged into the SBC with my cable. But, it isn't the SBC, as I get a solid image when using a standard VGA cable.

                              Any other ideas? This is really stumping me now..

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