Designing Circuit Boards

ajward

Hey Everyone...
Does anyone have a link to a SIMPLE tutorial for using Eagle to design circuit boards? I've tried using the program to create a simple board using a 78XX regulator to get a circuit board for various power supplies.
I've laid out the components in a as they might be drawn on paper, but when I try to create a circuit board, the traces criss cross the window like a child's scribbling!
Heck... if someone has such boards, I'd be happy to buy a few!

Any assistance would be greatly appreciated!

Amanda

Cluso99

Not sure what you want on your board, other than a regulator.

There are much better regulators out there than the 78xx.

Genetix

Amanda,

What current output are you expecting because you may need to heat sink the regulator and use thick traces?

Check and check and check again that your footprints match your physical parts!

I found these 2 Tutorials
https://learn.sparkfun.com/tutorials/using-eagle-board-layout
http://www.instructables.com/id/PCB-Creation-with-Eagle-for-Beginners/

And of course, here
http://eagle.autodesk.com/eagle/documentation

The more direct and straight connections that you can make pins, the easier it will be to route everything else so move parts around and remember that you can also ROTATE parts.

Which version of Eagle are you using?

Oh, by the way, that jumble of wires is what is called a "rat's nest".

Also, before you start routing are you sure that your schematic is correct and have you built and tested this circuit to be sure it works?
Nothing is worse than wasting time on a mistake.

T Chap

Can you post an image of the crisscrossing. What you describe sounds like rats nest and an unrouted board. You can press autoroute to route the board but there are parameters to learn to do that.

Wuerfel_21

One general tip for 2-layer boards: Use one layer mainly for horizontal, the other mainly for vertical traces. Saves a lot of hassle.

JLocke

Over at Sparkfun, they have a lot of tutorials on using Eagle. Try this link: https://sparkfun.com/search/results?term=Eagle+PCB. Then click on the bar that says 'Tutorials'. Should get you started.

localroger

Echoing what Wuerfel said, I would even say devote one layer exclusively to horizontal traces and another exclusively to vertical. Sometimes this will seem wasteful or strange; it's a straight shot after all at a 45-degree angle between two components, so why not take it? Because it is easy to back yourself into a corner where you are needing all kinds of vias to duck over and under such traces. This even applies to 4-layer boards, because the outer layers are generally power and ground planes. It's best to design the entire board this way with no diagonal traces at all, then when everything is hooked up see what shortcuts you can take to make more direct runs.

Genetix

Back in college I designed a Power Supply PCB when I was a lot more naïve about electronics so I have 2 questions that may be of importance to Amanda.
1.) Are ground loops a big concern and how would one layout a "Star" point (a common point that all grounds branch off from)?
2.) How close/far should the large electrolytic filter capacitors be from the regulators to be cool yet still function?

Oh, and Amanda you should consider using polarized or idiot-proof connectors instead of just wires or headers. This is known as Poke Yoke which is Japanese for mistake proofing.

Phil Pilgrim (PhiPi)

Wuerfel_21 wrote:

One general tip for 2-layer boards: Use one layer mainly for horizontal, the other mainly for vertical traces. Saves a lot of hassle.

That's generally true, unless you have a ground plane. With a ground plane you want to eliminate as many traces that cut it as possible. And, where traces are necessary there, you have to make sure the ground currents flow in a smooth way to the ground return connection at the power supply input. That's the feng shui of PCB layout. Even without traces in the ground plane, you might want to carve dikes into it to direct ground return currents from high-current loads around -- rather than through -- the logic section of your board.

-Phil

Jorge P

ajward wrote: »

Hey Everyone...
...
I've laid out the components in a as they might be drawn on paper, but when I try to create a circuit board, the traces criss cross the window like a child's scribbling!
...
Any assistance would be greatly appreciated!

Amanda

I think, just by what you are describing, you may just be seeing the un-routed "rats nest"/"air wires". YouTube has several really good videos by searching "eagle board layout tutorial"'s. What I think you are seeing is where the connections come and go to according to your schematic, aka "rats nest"/"air wires" which is what is will be called in documentation you are reading or may have read.

Genetix

I first heard the term rat's nest when I was designing that PCB for school and I never quite knew exactly what it was until I saw it when playing Diablo.

Picture a pack rat's collection of string, yarn, etc. all balled up in a pile.

ajward

Hey Guys...

Thanks for all the great answers!
I'll check out the links this weekend. Not looking for an industrial class PS, just something simple to charge a small handheld, dual-band (2m/70cm) radio from the 12v outlet in my car. Nothing elaborate, possibly just the 7810 and a couple of caps.
Yeah, I know I could just buy one but where's the fun in that?

Lastly (although there wasn't a firstly :->) I want to say how much I appreciate the vast amount of knowledge available on the forums!! I often have questions that stray from Parallax products but someone always seems to have a great answer. What an awesome resource!

Amanda Ward

Peter Jakacki

If you want 10V from a nominal 12V supply that can dip way below 10V and even sit close to 15V during charging you will need way better than a 7810. First off the 78xx series have about a 2V dropout so that's way some old supplies would have 7.5V or more feeding a 7805. Worse still though is a 7810 running from 15V with say 1A current, then that would be 5W that it would need to dissipate, and that's an awful lot of heat to try to get rid of, even with very low thermal resistance. That's why they used to have the exact same regulator in a big TO-3 package as a TO220 has a higher thermal resistance and hotspots can kill the regulator.

These days switching regulators are almost universally used and if it is simply for charging then you might not have to worry about low car battery volts. Maybe the 7810 will work fine, but it may get quite hot. BTW, don't copy circuits from the web that have big electrolytics on the output of the regulator as they may have uses on the input, but the reason for the regulator is that it ... well....regulates. Besides electrolytics have very poor response at regulation "frequencies" which is why most circuits will show a very small ceramic cap on the output and maybe a small tantalum that are effective.