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What does "JP" on a pcb mean?

Discussion in 'Electronics Homework Help' started by wolfgervdp, Apr 15, 2014.

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  1. wolfgervdp

    wolfgervdp

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    Apr 15, 2014
    Hi all,

    I have to write an essay about a digital bathroom scale. On the pcb there are two objects (altough I could maybe better describe it as "formations of copper") I don't recognize. One has the letters JP on it, the other has te letter "J". I encircled them in red, on the picture I uploaded.

    I was wondering what those things are, and what their functions are.

    Thanks in advance,

    Wolfger


    pcb_J2 and JP.jpg
     
  2. davenn

    davenn Moderator

    13,765
    1,920
    Sep 5, 2009
    Hi
    welcome to the forums :)

    JP = Jumper .... in this case on your board, its where a solder jumper can be made between the 2 PCB pads
    These may allow for various functions for region specific use ... eg ... lbs in the USA or kg for most of the rest of the world
    if its a clock module there may be one for permanent 12 hr or 24 hr setting

    Without knowing the manufacturing/design info for the board you would have no idea what they are for.

    Dave
     
  3. wolfgervdp

    wolfgervdp

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    Apr 15, 2014
    Thank you :)

    Ok, thanks for the info. I wouldn't immediately see where it is for, because this simple scale didn't use any of these settings. It only used kg, and there wasn't a clock in the scale too.. I already searched on the internet for more info about the board, but I had no luck finding it.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,477
    2,820
    Jan 21, 2010
    They were just examples.

    Maybe it allows the device to be used with a different pressure sensor.

    Maybe it does convert it to lbs.

    Maybe it changes the range from 0-200kg to 0-200g

    We don't know. We're just telling you the sort of thing it might be used for.
     
  5. davenn

    davenn Moderator

    13,765
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    Sep 5, 2009
    only the manufacturer is likely to be able to help you

    and they may not be willing to share their secrets :)

    Dave
     
  6. wolfgervdp

    wolfgervdp

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    Apr 15, 2014
    Oh yes, I see. So if I'm correct, you must have physical acces to the board to be able to use those jumpers? And shorting it with a screwdriver should "activate" those jumpers?

    I'll send an email to the manufacturer, they might be willing to give me some more information, if they're in a good mood :).
     
  7. wolfgervdp

    wolfgervdp

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    Apr 15, 2014
    I have another, quite different question about this pcb.
    Since there are capacitors in this pcb, does that imply that the current should be tranformed from a direct current to an alternating current? Because, with my limited knowledge of electronics, I do know that a capacitor will not let the direct current trough, but will just load itself, and then act as an open circuit.

    (If I should move this to another thread, please do tell me.)
     
  8. davenn

    davenn Moderator

    13,765
    1,920
    Sep 5, 2009
    its good here as its part of the same subject :)

    Most of those capacitors will be for grounding noise that appears at the inputs to that chip in the middle
    others will be for grounding noise that appears power rails

    We need to remove the noise from those lines so that that noise doesn't cause
    "glitches" (error) in the circuit operation

    capacitors have many functions in circuits, depending on their values and how they are used
    including smoothing, decoupling between stages, oscillator circuits

    cheers
    Dave
     
  9. wolfgervdp

    wolfgervdp

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    Apr 15, 2014
    Okay,I see how the capacitors could ground that noise. But still, when this circuit would just be using DC, it wouldn't work, would it? The current should somehow fluctuate for this circuit to work? There is a capacitor immediately after the power supply. How could there flow a current with that capacitor there? Shouldn't that block all the current? Or am I just completely mistaken?
     
  10. gorgon

    gorgon

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    Jun 6, 2011
    Inside the big black blob there is a small microcontroller. This controller has a clock that drives the digital part of the circuit. To cancel all noise from the internal and external signaling you use capacitors for decoupling. Even if this is not an actual AC voltage, it is in fact an alternating DC voltage, or voltages. Each individual signal that change state over time emits noise to the power supply line, and the capacitors will by nature 'short' away this noise.

    In addittion to this, the weight cell(s) that measure the load of you on the scale, use very small signals that needs to be protected from 'drowning' in the noise from the digital clock driven part of the circuit. This is done by using capacitors and other components.
     
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