I'm working on a design shield and have a "tricky" dimensional question. I don't have a Duemilanove in front of me to test, though that's the platform I'm ultimately designing for.
Here's the problem: I need a coin cell on the shield, but I want to put it on the "bottom" (the side that faces the Arduino) to preserve space on the "top" for other components.
It looks like clips for 12mm cells are available that are 2.34mm tall. Is there enough room? It looks like there would be enough room up by the digital headers, but since I can't actually measure, I'm not 100% sure. The holder is 13.2mm in diameter.
Short of me ordering a Duemilanove and waiting a week or two, can someone let me know if this would fit? Anyone done this before?
You could also potentially use longer legged headers to raise the shield up higher from the Arduino. Another possibility is to buy a Seeeduino, which uses all SMT components (it would give you more room).
The headers on the Arduino Duemilanove are 8mm high, and the circle in the picture below is 13mm in diameter. The circle could fit anywhere in that upper part of the board between the right edge and the USB connector, or in the area near the voltage regulator, though you probably want to avoid any heat over there. There is not enough height above the ATmega328 itself to fit anything. Still, you should have no problem finding a place for your coin cell on the bottom of your PCB.
If you want to scale your own drawing, you can use the picture at http://arduino.cc/en/Main/ArduinoBoardDuemilanove. According to the bottom of that page, the PCB for the Duemilanove is 2.1 inches (53.3mm) from the top edge to the bottom edge, and 2.7 inches (68.6mm) from left to right. My cheapo ruler confirms that closely enough.
Don't forget to consider that your shield may not be stackable with other shields unless it is the bottom of the stack.