Ground layer on boards

Hello,

I've noticed that a lot of breakout boards and such that you can buy don't have traces for the ground connection. Why is this okay and how can I recreate it if I were to order a custom board.

Would I just not connect the cathodes of leds and such to a trace and just leave them soldered to the board?

Most boards contain a ground plane which a bunch of copper used as the ground node. So there's no need to run a trace anywhere.

So if there is a copper pad, that is in turn connected to the rest of the board.

I guess what i'm getting at is can I just run power to anodes of leds and not have to deal with the cathodes if I have perfect v=ir going?

guess what i'm getting at is can I just run power to anodes of leds and not have to deal with the cathodes if I have perfect v=ir going?

Do you mean with no resistor for the LED?

I mean with resistors

You have to use resistors for LEDs.

You must ground the cathodes... connect them all together and connect them to ground.

Doc

well if you see the resistor on pin 13, this is the board schematic for the duemlanove. They don’t have the cathode connected to anything.

It's because it is connected to the ground plane, which isn't visible in that image. EAGLE doesn't draw the ground planes until the user runs the RATSNEST command.

Intresting, when I ran RATSNEST, all it did was show a red grid across the entire board. Is that the ground plane? The thing I don't understand is how there is now via to a different layer.

Yes, its the groundplane (which can be solid or gridded as in the Arduino). Red is top-side copper. Solid groundplane is preferrable for heat-sinking purposes, high-current and for RF groundplanes. Grid-style uses less copper (PCB fabs reclaim all the etched copper for re-use).

so it is just the literal metal beneath the top layer? So its automatically connected to the ground plane?

.< so confused.

funkyguy4000: so it is just the literal metal beneath the top layer?

It isn't a special layer. A layer on the PCB is a layer of copper. If you etch that layer into traces, you have traces. If you etch it into circles for a via, you have a via. If you just draw a polygon it is called a plane. Naming it GND or Ground or whatever, makes it a "ground plane."

So what that grid is on the Duemilanove is just the left over area that isn’t a specific trace and they made a big grid of traces that connects to ground? So it wouldn’t be any different from me just connecting each ground together with a single trace. Correct?

Sorry I’m being…difficult, my brain is totally failing me tonight

funkyguy4000: So what that grid is on the Duemilanove is just the left over area that isn't a specific trace

Yes, not a specific trace, but a specific node: ground.

funkyguy4000: So it wouldn't be any different from me just connecting each ground together with a single trace. Correct?

Effectively, yes.

Okay, hmmmm. I’ll have to see if it would be less stress to just do that or try to work out a big highway called ground.

Thanks for all the help!! I really appreciate it.