Mystery object!

[quantum1]

A strand of metal wire populates some of the area on the pcb I have, and many others. It is plainly labeled "J" on the pcb. It has zero resistance, and I wonder if it just to carry current that can't get through the without short/parallel the circuit, just like a zero ohm resistor. Why is it labeled "J"?

 

[audioguru2]

Hi Quantum,
It is a "J" for Jumper.
It avoids the expense of having a double-sided PCB. I have seen them that look exactly like resistors, with a single black ring that means "0" or "zero" ohms. A little one probably has a huge power rating.

 

[MP1]

It is not always to avoid multi-layer boards. You will also see this on many of the multi-layer boards. Some manufacturers use the same board layout for many different devices. In some cases, the resistor values will be different than on the other board models and in some cases, the resisotrs will not be needed at all in some places of the design for certain models. In these cases where a resistance is not necessary, the jumper is used to complete the circuit. This is very common when you design a board which has the choice of giving a current output or voltage output, for example. In one choice, you will not need a particular resistor, so you just use the jumper in it's place.

MP

 

[audioguru2]

Yes that's right, MP. I forgot about that.
Also, some jumpers have a raised kink in them so that they can be cut to disable functions, instead of using an expensive switch. OOps, you cut the wrong one. I hate having to solder them back together in the field.

 

[quantum1]

It is not always to avoid multi-layer boards.

What are multi-layering boards? How would you draw a schematic for a multilayer board, possibly ones with SMD's. Websites containg pictures are always helpful.
Inquiring mind needs input.

 

[harsh2]

the schematic would look the same as any other schematic..
the layout of the board would require software with different layers superimposed on top of one another..dont ask how they MAKE a multilayer board.. cuz i know not...
but if u look at an old pc card , video or otherwise, hold it up to the light there is holes in it... those holes connect the layers...