Modifying the Shape of an Arduino - Building Open Source Hardware - page 104

Place Mechanically Constrained Components First
Any components with mechanical constraints in your assembly should be placed precisely
in the model, and the remaining components should be organized around them. For ex-
ample, with the Replay boards, the position of the audio jack was critical, so it was the
first component to be added to the board. Additionally, if you're designing a housed board,
place components that you need quick access to accordingly so that you can easily access
them once the board is fully assembled into its enclosure.
Leave Space for Any Necessary Programming Headers
Burning a bootloader onto your microcontroller is much easier when you have headers that
you can easily connect to your ISP, so make sure to reserve room for these headers. The
downside of incorporating these headers on your Arduino derivative is that they unneces-
sarily take up space after the bootloader is downloaded. Alternatives for conserving space
include designing the board so that the headers can be easily detached and physically sep-
arated from the board and designing a separate board solely for burning the bootloader on
the microcontroller before it's transferred to your custom Arduino derivative.
Leave Clearance for Screw Caps
If you plan to use screws to fasten your board to the enclosure, ensure that you leave
enough clearance for the screw caps to prevent shorting traces on your board. A manufac-
turing process that incorporates a solder mask can assist in preventing shorted traces on
your board.
Double-Check by Creating a Printout to Scale
As Amanda Wozniak pointed out in Chapter 5 , once you've finished your board layout,
youcanprintouta1:1scaled drawingoftheboarddirectly fromEagle. Printing yourboard
layout and cutting it out is an incredibly useful way to test whether your board and its com-
ponents fit as you expect. It is especially helpful if you have a prototype of the enclosure
on hand and can check whether the board outline fits inside of it.
Moving from Eagle to CAD
If you prefer to start from Eagle rather than a CAD package, you can export a DXF file of
your board directly from Eagle (under File > Export > DXF ). This requires that you draw
the board outline in the Dimension layer of the Eagle program. After specifying the units
of the file, you can then import the DXF file into your CAD package and build your model
around the board.