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Discussions relating to Electronics 101.

Discussion in 'General Electronics' started by Tweakie, Oct 14, 2014.

  1. Tweakie

    Tweakie OpenBuilds Team
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    As Electronics 101 is now starting to come together and I only have a few more items left to add I thought it would be good to now have an area for discussion - perhaps relating to some of the more controversial points I have made or suggestions for additional points that we think should be added - so guys, it's over to you. :)

    Tweakie.
     
  2. David the swarfer

    David the swarfer OpenBuilds Team
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    grounding guidelines , esp for signal wires to prevent crosstalk and ground loops.
     
  3. Tweakie

    Tweakie OpenBuilds Team
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    Thanks David - a good suggestion. :thumbsup:

    Tweakie.
     
  4. Paruk

    Paruk Master
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    To illustrate the effect of grounding or not I thought about posting this short video



    Hope it helps to clarify the issue of grounding.:)
     
    Daragh likes this.
  5. Tweakie

    Tweakie OpenBuilds Team
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    Hi Paul,

    Thanks for posting the excellent video which clearly demonstrates the need for screened / shielded cables for inputs such as limit / home switches etc. and also the importance of only connecting the shield at one end. :thumbsup:

    Something else that should also be taken into consideration is the type of screened / shielded cable used with the braided screen types being preferable to the foil screened types.


    Tweakie.
     
  6. Paruk

    Paruk Master
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    I just bought some shielded speaker/audio cable that has that braided shielding. Planning on using that for all the wiring. Also bought some triple shielded, pure copper network cable from a locally famous electronic shop chain. Made in China! Have a laugh. I cut the RJ45 off to see what it was, no shielding at all, metal or maybe aluminum wire inside, not even of the good type for getting RJ45's on. Yindee to Thailand, the country were lying on big scale is more common than your 0 volt star grounding!;) Man, it is a mess to get relatively good stuff here.
     
  7. Paruk

    Paruk Master
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    Looking into this matter, I'm more and more convinced that most of my present problems with the Buffalo are traceable to the grounding issue.
    Beside the use of shielded cables for all connections, I'm going to split the wiring; all signal input cables (limit switches, tool sensors etc.) are going to be lead along the right side of the machine, while all power cables with high current will be lead along the left side. This way I hope to avoid as much noise as possible.
     
  8. Tweakie

    Tweakie OpenBuilds Team
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    Sounds like a very sensible plan. :thumbsup:

    Tweakie.
     
  9. slittle

    slittle Journeyman
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    Pricey but Aircraft Spruce has some quality shieldwire
     

    Attached Files:

  10. Paruk

    Paruk Master
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    Yep, if I only would have known before…….:) But this topic should be spun out to give people the info they need to avoid the mistakes. Electronics 101 should be as no.1 on the hit list here.
     
  11. DazTheGas

    DazTheGas Journeyman
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    Now heres something that has been puzzleing me for a while??

    should all psu`s gnd (not earth) be conected together, im using a pc psu for my 12 and 5v and a 24v for steppers. now i have a board that uses both 12v and 5v inputs with optocouplers between the circuit, by using the pc psu is the 5v side still protected from the 12v as the gnd in the psu are joint.

    If its ok then should i connect the 24v gnd to the 5v and 12v??

    Like I said puzzled.

    DazTheGas
     
  12. Rob Taylor

    Rob Taylor Veteran
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    Ground = Earth, so I wouldn't use that nomenclature when you mean the 0v rail, that's just confusing and potentially dangerous. "0v" isn't necessarily 0v with respect to ground, merely that it's -Vcc/Vin with respect to the Vcc/Vin line. If it's actually labelled GND on both power supplies, then it should be grounded to the PSU case- in which case, tie them together by all means, because the 0v rails are all at the same potential. Check for continuity between the GND "output" rail and the actual physical ground/earth pin on your mains plug before you do so though. If both PSUs don't have continuity to ground, I wouldn't tie them together. There's no real need to anyway, and you risk creating an unforseen potential somewhere unexpected.

    If you mean that the ATX PSU is supplying both sides of an optocoupled circuit, that's fine, since each side is separately regulated, even with a common 0v rail/ground line. 0V cannot apply any voltage to the circuit, it's a current sink, even if it's technically not a ground, because there's no part of the circuit with a lower potential (crazy inductor-based voltage spikes notwithstanding).
     
    Joe Santarsiero likes this.

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