This project is about designing a PCB for the Atmel SAM3X8E with the Open Source layout editor KiCad . The result is a kind of Arduino Due Clone, since the MCU is the same and I also have tried to get a similar pin mapping.
I have until now designed quite some PCBs with Eagle  from CADSoft and was happy with the software. But since my designs are getting more and more advanced, I start to get limited by the 8 cm x 10 cm size limitation in the light version. The Hobbyist version would increases the size to 16cm x 10 cm for around 169$. Further it would be nice if one could move around a set of tracks, when a little bit of space is needed for another track. In Eagle one has to move every track individually.
Looking around for alternative PCB software, which does not have these limitations, I found KiCAD, which had improved in the last time, since developers at CERN started to take part in the development . With the support of CERN, KiCAD will have a big future. Already now it goes in the direction of ALTIUM, even if it is not yet there.
Features which made KiCAD interesting for me:
* Hierarchical Schematics
* Unlimited size and many signal layers
* Push and Shove router
* The whole editor makes a very professional impression
* More flexibility in the designs
So I believed in KiCAD and started with the schematic design.
The schematics sheet with the micro-controller is shown in the next figure.
The whole schematics can be viewed as a pdf Schematics
After the schematics comes the layout of the PCB. This went very smooth after getting used to the key combinations and functions available. One announcing thing are the different render modes, providing different functionality.
But I expect this to be more uniform in the future.
In the design rules I allowed the following minimal settings:
|Minimal Track Width||10 mil|
|Minimal Via Pad Diameter||40 mil|
|Minimal Drill Diamter||0.45mm|
These are the limits what I’m able to fabricate at home with my etching process.
At the end the PCB looked the following:
Very nice is the export of the PCB from KiCAD into a PDF for printing on a transparency.
The two layer PCB was exposed on my light board, developed and etched. Via holes were drilled, small silver wires are pressed into the holes as described in Flat VIAs for double sided PCBs and the whole PCB was tinned as described in PCB tinning including VIA soldering.
The vias which are not under the IC were additionally solder for better/saver contact. Holes for the through hole parts were drilled and the PCB was soldered.
For those who wonder why the USB-B contact is on the wrong side, this is due to an error of the footprint in KiCAD.
This issue is fixed in Rev 2 of the PCB (not etched yet).
The final PCB has a similar pin mapping as the Arduino Due
During soldering the track of pin PC1 loosened from the PCB and Pin PB14 seems to have a broken via under the chip.
The rest of the pins has contact and seem to work as expended.
Differences compared to the Arduino Due Mapping:
|PC1:||Track loosened from the PCB (only effecting my PCB)|
|PB14:||is dead due to a cold soldered Via under the chip (only effecting my PCB)|
|PA28||is connected to Pin 10, the Arduino Due has additionaly another output pin connected to Pin 10 – PA28 (digital 77)|
|PA29||is connected to Pin 4, the Arduino Due has additionaly another output pin connected to Pin 4 – PA29 (digital 87)|
For me KiCAD is definitely the preferred PCB editor compared with Eagle and I plan to start future projects with KiCAD instead of Eagle. (Some projects are still started in Eagle)
Files can be found on GitHub
It can be checked out with:
git clone https://github.com/digibird1/ArduinoDueClone