Jumper wire vs. long pcb traces

Discussion in 'General Electronics Chat' started by infidelboy, Jul 13, 2013.

  1. infidelboy

    Thread Starter New Member

    Aug 8, 2010
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    I work with single sided PCBs and sometimes i feel comfortable in adding few jumpers in place of long round traces.

    I want to know if it is a good practice or not, or is there anything i need to worry about.

    If not, is it okay if i go with round and long traces?
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    The whole point of a PCB is to eliminate hand wiring so I don't get your preference.

    However, if the wire is either insulated or constrained to keep it from moving and shorting otrher parts then it should work. I just would not do it that way. Ever.
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    No problem at all. The last two traces are always the hardest to route.
    A couple of jumpers will save the day. Just consider them as 0Ω resistors.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    If you are talking about doing a jumper to shorten a long trace, that's generally only needed for high frequency RF signals or fast transition time digital signals. For video and audio frequencies the board trace length seldom has a significant effect on the signal.
     
  5. madmantrapper

    New Member

    Apr 20, 2011
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    I've seen it and done many times.
     
  6. infidelboy

    Thread Starter New Member

    Aug 8, 2010
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    Thanks you all for your replies.. one more thing..
    is there any extra inductance or capacitance to worry about in case of jumpers at high frequency?
     
  7. monster_catfish

    Active Member

    Mar 17, 2011
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    It is good news that the odd after-thought jumper wire is alright to use, since I wound up having to add my decoupling caps, which I originally thought I wouldn't need, in this manner, with heat-shrink on the cap legs to ensure there are no problems with shorts between the cap leads and the board traces.
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    This is not a good idea for decoupling capacitors. For caps to do their function properly they should be installed with the shortest leads possible very close to GND and Vcc pins or whatever pins you are trying to decouple. Long leads add inductance to the filter cap.
     
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  9. crutschow

    Expert

    Mar 14, 2008
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    Decoupling caps are standard design practice for all circuits. Why would you think you didn't need them? :confused:
     
  10. monster_catfish

    Active Member

    Mar 17, 2011
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    Thanks for this timely caution, Mr. Chips. Until you mentioned not to do so, I had fully intended to remedy my careless oversight by soldering in the caps to a board on which I had neglected to include traces for decoupling caps. Now I think I'll be better off just having new boards made up by Express PCB, with nice short decoupling cap traces included.

    Crutschow I was under the mistaken impression that decoupling caps were only essential for high frequency and RF applications. My data-book circuit adaptation, being just four simple DC opamp inverting ampliers connected to process the gradually varying output voltages from pots rotated by the levers in my DIY USB flight simulator throttle quadrant, wouldn't need decoupling caps, or so I thought, prior to the time I noted how noisy and inconsistent my output voltages were.

    Oh well, I suppose Express PCB will be glad to make me another set of PC boards. I'm almost tempted to ask them for a negligent noob's discount on this next order of amended PCBs, but I imagine that suggestion would only amuse them.
     
    Last edited: Jul 15, 2013
  11. Brownout

    Well-Known Member

    Jan 10, 2012
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    When prototyping, I sometimes solder chip capacitors directly to the IC pins, or else use short wires directly to the pins. If your VCC and ground pins are close, you might just try that.
     
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  12. monster_catfish

    Active Member

    Mar 17, 2011
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    I'll give this a shot, Brownout. I may be able to salvage the board by soldering the decoupling caps directly to the IC socket pins. Looking back on my folly now, I could have simply included tinned through-holes on traces close to each chip's VCC pin, and soldered the caps between those holes and the power strip.

    Hindsight is 20-20. Reminds me of the lyrics to an old Randy Travis song. Hope he pulls through his present medical state to sing many more songs for more years to come.
     
  13. MrChips

    Moderator

    Oct 2, 2009
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    A perfect design is a good thing but there's nothing wrong with second best solution.
    You can still try using capacitors with axial leads and solder them from pin to pin on the bottom side of the board. Still better than nothing.
     
  14. monster_catfish

    Active Member

    Mar 17, 2011
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    I don't like to throw away a perfectly good, un-used PC board, so I will try this fix for sure, Mr. Chips, and post a comment back here if it solves the noise problem. The board is small, measuring the standard 3x5 inches, so the decoupling cap won't be straddling a long distance between the IC's power pin and the board's power plane.

    I sure look forward to trying out my throttle quadrant, as quite a bit of metal-shop work went into fabricating the housing and levers, before I temporarily moth-balled the whole thing on account of that pesky noise problem in the output voltages.
     
  15. MrChips

    Moderator

    Oct 2, 2009
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    If I saw your PCB layout, top and bottom, I may be able to provide better advice.
    If there is a ground plane you might be able to drill one hole in order to connect the cap to the ground plane.
     
  16. monster_catfish

    Active Member

    Mar 17, 2011
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    I appreciate this offer, Mr. Chips. I'm about to try and post the schematic and Express PCB board layout that I used. Photobucket is proving difficult to navigate today for some reason. This will take a few minutes.

    [​IMG]
     
    Last edited: Jul 15, 2013
  17. BobTPH

    Active Member

    Jun 5, 2013
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    Murphy's law in reverse:

    I had my first manufactured PCB come back and it almost worked, but I needed a tank capacitor on the input power. It turned out both power and ground had a via near where they came in at a spacing of about .1 in. So I just soldered a 10uF electolytic into the two vias. I don't expect such luck in the future.

    Bob
     
  18. monster_catfish

    Active Member

    Mar 17, 2011
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    Now this is frustrating. I have so far been able to post the schematic, which is of limited use for this decoupling cap question, but when I try the same steps with the Express PCB board layout, the closest thing I can get cto post is a component layout that does not show the traces.


    I'll keep working at this though...It looks like I'll wind up scanning a printout of the Express PCB board, and then save it as a .jpg image which I can then upload to Photobucket, and finally to this thread. There has to be an easier way, but I can't see it right now.

    Ah, at last.

    [​IMG]
    .
    Sorry about the sideways orientation. Photobucket had me pulling my hair out for a while there, and this is the best rendition of my PC board that I have been able to post here so far.
     
    Last edited: Jul 15, 2013
  19. crutschow

    Expert

    Mar 14, 2008
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    .jpg files tend to make drawing details look fuzzy. Try to post in a bitmap format such as .gif. Those can be posted directly to this forum, you don't need to go to Photobucket first.

    Do a screen-dump of the image to you clipboard by pressing "Alt-PrtScn" on you computer. Then transfer the clipboard image to your photo-software such as Paint, for editing and saving in the desired format.
     
  20. MrChips

    Moderator

    Oct 2, 2009
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    Ok, this is easy.

    Put 0.1μF cap on bottom side between pin-4 and pin-11 on U1 and U2.
    Use axial ceramic cap. Radial will also work too.

    Put one 10μF to 100μF axial aluminum electrolytic from +5V to GND at the power rails. On the component side, at the right hand side of the PCB would be ok. Don't worry if the leads are long.
     
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