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Thread: how about this: grounding produces noise

  1. #1
    Maximum Bitrate
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    how about this: grounding produces noise

    I was reading the other thread about grounding the lilliput vga connector to reduce the flickering. So as we know the vga connector attaches to the VGA port of the computer case, hence all around that area would be ground.

    I checked the resistance between there and my car body (actually to one of the screws that bolts my seat to the car body) and found it to be around 4 KOhms. I thought, hrmm, that's too high.

    So I ran a wire from the screw-bolt to the vga connector and attached it to the vga prot screw, and found the resistance to be about 3 ohms. (voltage difference between the screwbolt and the vga connector about 0.15V)

    But now.. I get alternator noise! Which wasnt there before (maybe it was but I didnt notice it). It didnt fix the lilliput flickering either.

    Possible problems?
    1) That screw-bolt is not really car body
    2) difference in potential between amplifier to CPU, or between preamp to CPU
    3) quite lengthy ground wire (about 20 cm)
    4) ground wire is quite narrow in diameter, about 1/3 the diameter of the power wire.

    Hrmm, I could fix this problem by just removing the ground wire, but I dont want to hide the problem.. i wanna fix it for real

  2. #2
    Raw Wave Confused's Avatar
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    The problem is that you've now introduced yet ANOTHER ground point into your system. You've got the PC ground, the lilliput power ground, plus this ground from the vga connector.

    Wire up the power of the screen to the output from your PSU, and make sure that is grounded, and you should be fine.


    Garry
    Co-Developer of A.I.M.E.E
    www.aimee.cc

  3. #3
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    I dont think the lilliput is grounded at all before this connection.

    The PC case wasnt grounded either. It was when I grounded the PC case together with the lilliput that I get this problem.

    By your suggestion, you mean the output of my PSU should go to my mobo and my lilliput? The excalibur chip I use to moderate the 12V incoming voltage is rated at 1.5A I believe, and I think the cpu is using a lot of that juice already

  4. #4
    Variable Bitrate mutilator's Avatar
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    heh my bros install, we wired the pc +12v, before the -12v, and it started up anyways.. (must of been grounding through VGA) took a while to figure why the picture was so flickery etc (id assumed hed grounded it, he assumed i had...

    its best to ground everything in 1 place as far as i know.

    tom.

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