I've been playing with an SD-shield from Adafruit lately, but there are loads of great shields out there developed with the sole purpose of developing your own application with it (I'm thinking of Sparkfun and Adafruit for starters, who have these great motorshields, display shields, GPS-shields, etc...). The great part is: all these designs are out there under Creative Commons licence. The source files (both schematics and PCB board design) are out there to download. All you need is load them into EAGLE CAD, to play with them...
And now, that's exactly what we're going to do...
Some cool starting shields of which you can download the EAGLE files
These are just a few of the shields out there to start off with. Depending on the project you're working on - this or an other shield might answer to some of your needs.
- Adafruit Data logger shield: https://github.com/adafruit/Data-Logger-shield (SD-card, real-time-clock)
- Adafruit 128x32 I2C OLED Breakout: https://github.com/adafruit/Adafruit-128x32-I2C-OLED-Breakout-PCB (mono OLED display)
- Sparkfun microSD Shield: https://www.sparkfun.com/products/9899 (micro-SD)
- Sparkfun Ardumoto shield: https://www.sparkfun.com/products/9815 (control up to 2 motors)
Having them in EAGLE CAD
First thing you'll do, is just create a new project - give it a fancy name, and don't forget to add a description.
Now, you'll just need to drag the 2 files (possibly inside a zip-file) into the project folder... the content will appear in your project. The .sch file is the "schematics" file - the .brd file is the board file (PCB).
Firstly, open the schematics file, and remove all the components that you won't need - it might free up some ports - and obviously it will save you some space.
Now, if you go to the board-view, you can start removing items you want to get rid of (holes, text, about anything except components and routes).
To remove the lanes, you just right click on a lane and select "ripup". This will cause the route to disappear, and a simple airwire will appear. After removing all obselete lanes, select the options "ratsnest". This will recalculate all the required connections (airwires) and consequently remove the airwires no longer in use.
Obviously, be careful not to remove too much :)
Sparkfun and Adafruit licence their boards under Creative Commons Attribution, Share-Alike. This means you're allowed to make derivative works (your own PBC) and even sell it - but you need to attribute the original - and you must offer the source files freely too.
The light version of EAGLE CAD is allowed for non-profit or evaluation use. If you earn (or save) money by using the Freeware version of EAGLE Light, you have to register it. So if you make money off your project, you're required to buy a version of EAGLE CAD (www.cadsoft.de or www.cadsoftusa.com)
So basically, if you're working on a project for an Arduino shield for your own leisure or for learning purposes... you're free to go!
A set of 2 videos as a great tutorial on EAGLE CAD