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PCB Tools Overview

Michael Ang and I are teaching a DriveBy at ITP on Monday the 13th about electronics without breadboards, which is to say PCB design, production, and surface mount soldering. In the meantime, I thought I'd give a quick overview of my toolchain from PCB design to production. More details to come, both at the DriveBy and on this site. But for now...

PCB Design

CadSoft Eagle (Mac version requires X11 from Apple)

The freeware version of this package lets you draw boards up to 4" x 3.2". It's a great package, with solid part libraries, and good functionality to easily add your own custom patterns. It's equally at home with surface mount or through-hole designs, and it's the tool we will focus on at the DriveBy.

There are a few quirks to the interface that take some getting used to. First, in order to act on a group defined by the Group tool, you need to right click. On the Mac, this is substituted with a command-click (Make sure 'Emulate three button mouse' is active in the X11 Preferences). So to move a group of items, group them with the Group tool, then switch to the Move tool, command-click, and you're off.

Secondly, the Copy tool oddly only works with single items. To copy a whole group, you first use the Group tool to select them, then switch to the Cut tool. Command-click (note that this doesn't cut in the sense that Windows users are used to, but actually is more like copy), and then switch to the Paste tool to lay down the copy.

The next stumbling block is getting your files exported in the right format to get PCBs manufactured. Virtually always this means Gerber files. Here is a good tutorial from SparkFun about this. For my recent project, a 3D dimensional spherical surface display (PCB shown at left), I actually used the .cam file from the tutorial to do my export. The job is still processing, so we'll see how it goes.

Panelizing Jobs

For my last few projects, I have used Gold Phoenix PCB for production, and have been very satisfied with the service. They can go down to 4 mil trace/space (for an extra fee), and also have cool extras like colored soldermask (also for an extra fee), and a good expedited service (also for an extra fee - surprise?).

The special at Gold Phoenix typically is for one board of around 1 square foot. This means that, since the free version of Eagle can't handle designs over about 3"x4", we need a way to combine multiple designs after the fact into one panel.

GerbMerge to the rescue. This is a Python app that takes the Gerber files exported from Eagle and combines them into a single design using random placement to find a near-optimal layout.

It requires mxBase 2.0.4 and SimpleParse to install. Once installed, you control it using a configuration text file, which you have to customize to the specifics of your project (filenames, number of copies of each board, etc.). There is a sample configuration file in the documentation that will help you get started. Here is mine from this last project, if it might help.

Viewing Gerbers

Finally, once your boards are designed and panelized, you will want to take one last look at your files to make sure that all is correct before sending them (and your money) off to have the PCBs fabricated. There are a number of ways to accomplish this, but my favorite of the moment is gerbv, an open source package created specifically for this task.

There is a Windows port linked from the SourceForge page, but for Mac, the easiest way to get it is through DarwinPorts. It grabbed a whole list of dependencies for me completely seamlessly. You will have to add /opt/local/bin to your path if it isn't already included, though.

When it is all installed you can run it with the files you want to see as command-line parameters, giving you a view of your output files like the one shown here.

More...

This skips about 99% of the process of designing a board, but hopefully will be helpful in getting some tools setup and being able to start playing. Again, the DriveBy on Monday the 13th will cover this and more in more detail, so come with your questions or feel free to post them in the comments to this entry.

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