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What is the point of zero ohm shunts? — Parallax Forums

What is the point of zero ohm shunts?

Martin_HMartin_H Posts: 4,051
edited 2012-01-29 07:56 in General Discussion
I recently soldered a pcb kit which included a few zero ohm shunts. They looked like resistors with a single black band and were used for things like bypassing the voltage regulator when using a regulated power supply.

What I found mysterious is why use them over a bit wire?

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-01-27 18:56
    The reason for including them in a PCB layout is that they can be installed, when appropriate, with a pick-and-place machine. A small bit of wire cannot.

    -Phil
  • Martin_HMartin_H Posts: 4,051
    edited 2012-01-27 19:01
    Thanks that makes sense.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2012-01-27 19:18
    Anybody else ever been told how "0-ohm resistors" (one band, black) were devised because "jumpers" as such weren't allowed on old mil-spec pcb's?
    [Jumper = No; 0Ω resistor = OK ]
  • localrogerlocalroger Posts: 3,452
    edited 2012-01-27 19:44
    If the circuit board doesn't have solder mask, there is a risk of a jumper wire shorting to the trace it's jumping. Zerohm's don't do that.

    Saw my first Zerohms in the docs for a HP2100A minicomputer circa 1974 in my father's physics lab. They were soldered in place to do peripheral configuration.
  • TubularTubular Posts: 4,715
    edited 2012-01-27 20:02
    They also buy a little extra flexibility with regard to number of layers. The ability to use 0 ohm shunts (and jump a track) can be the difference between having to fabricate 1 layer vs 2 layer pcbs.
  • ercoerco Posts: 20,259
    edited 2012-01-27 20:07
    http://www.ebay.com/itm/ZERO-OHM-Resistors-Lot-50-0-0-Ohm-Jumper-BONUS-/230736589626?pt=LH_DefaultDomain_0&hash=item35b8f8f33a

    Fifty zero ohm resistors costs ~$7. Sometimes less is more, more or less.

    So how do you figure the power rating (I squared R) for a zerohm? :)
  • MoskogMoskog Posts: 554
    edited 2012-01-28 01:02
    erco wrote: »
    http://www.ebay.com/itm/ZERO-OHM-Resistors-Lot-50-0-0-Ohm-Jumper-BONUS-/230736589626?pt=LH_DefaultDomain_0&hash=item35b8f8f33a

    Fifty zero ohm resistors costs ~$7. Sometimes less is more, more or less.

    Could not resist, had to buy.
    No my homemade pcb's will look more professional with resistors instead of all the jumpers, haha!
  • ajwardajward Posts: 1,130
    edited 2012-01-28 02:07
    Thanks for the explanations! The first time I saw one of them was a wtf moment!

    @
  • Mark_TMark_T Posts: 1,981
    edited 2012-01-28 05:23
    PJ Allen wrote: »
    Anybody else ever been told how "0-ohm resistors" (one band, black) were devised because "jumpers" as such weren't allowed on old mil-spec pcb's?
    [Jumper = No; 0Ω resistor = OK ]

    That makes sense - in a high-vibration environment jumper links will work loose and fall off...
  • ElectricAyeElectricAye Posts: 4,561
    edited 2012-01-28 08:27
    erco wrote: »
    ...

    Fifty zero ohm resistors costs ~$7. ....

    So how do you figure the power rating (I squared R) for a zerohm? :)

    That's simple. You equate Power to dollars per ohm.
  • RDL2004RDL2004 Posts: 2,554
    edited 2012-01-29 06:14
    That makes sense - in a high-vibration environment jumper links will work loose and fall off...

    I'm just curious, how does this work? Other than the small blob of plastic in the middle, there doesn't seem to be any difference between a jumper and a zero ohm resistor.
  • skylightskylight Posts: 1,915
    edited 2012-01-29 06:21
    Phil Pilgrim (PhiPi) wrote: »
    The reason for including them in a PCB layout is that they can be installed, when appropriate, with a pick-and-place machine.
    Do they fit ok? I was led to believe that they are......a little short.

    Sorry i'll get my coat.
  • Martin_HMartin_H Posts: 4,051
    edited 2012-01-29 07:19
    RDL2004 wrote: »
    I'm just curious, how does this work? Other than the small blob of plastic in the middle, there doesn't seem to be any difference between a jumper and a zero ohm resistor.

    I am tempted to sacrifice one of them for science to see what is inside. My guess is that the wire goes straight through and the plastic is window dressing around it. I like the idea of using these as jumpers to avoid short against a trace as that has happened to me.
  • doggiedocdoggiedoc Posts: 2,245
    edited 2012-01-29 07:43
    skylight wrote: »
    Do they fit ok? I was led to believe that they are......a little short.

    Sorry i'll get my coat.
    I found that to be humorous.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2012-01-29 07:56
    Martin_H wrote: »
    I like the idea of using these as jumpers to avoid short against a trace as that has happened to me.
    The alternative, assuming a piece of solid wire, is to cut a piece of nylon tubing or stripped insulation.
    Or, take the time to cut and strip the wire precisely. A lead forming tool is inexpensive enough and can aid the process.
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