Fanout Board for ATSAMD21E18 MCU

A board for familiarization and early development

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This board supports basic Atmel ATSAMD21E18 MCU development. It has the MCU, crystals for both external oscillators, a USB connector, an SWI/JTAG connector and header pins for all of the MCU I/O pins. The reason that I built it is for getting familiar with this small, modest cost MCU and doing early development on projects based on it. There are other boards available that use this part, but by building up this board, I can check all the schematic and PCB footprints and have a useful board that does not have any associations with it's name.

This is a simple little board. It has all of the parts on it to exercise the features of the MCU like the external crystals and USB connector and all of the I/O pins are available on header pins. The crystal pins are shared with the I/O  and somewhat sensitive to external capacitance, so there are 3 position jumpers to allow routing them to the crystals or the header pins. Similarly with the USB connector. Jumpers are solder down 0 Ohm resistors to minimize board space and parasitic capacitance.

The SWI/JTAG debug connector used is a 0.050" spaced header that is much smaller than the 0.100" connector that I have been using for ARM projects in the past. Seeing it on this board makes me wish that I had done this years ago. Oh well...

OSH Park did the board fabrication (4 layer) and the first one has been populated. Initial testing looks good, all the oscillators work at the expected frequencies and the debugger hooks up and works.

If anybody is interested in using this board, I can make the files available at OSH Park.

Getting somewhat familiar with this parts basic system stuff like clock generation reminds me why people tend to stick with parts that they are familiar with. I have been through this process a number of times, and it still takes a real chunk of time to do for each device family.


Bill of Materials with Digikey part numbers.

Comma-Separated Values - 1.53 kB - 12/21/2017 at 14:18



Schematic diagram of board.

Adobe Portable Document Format - 208.24 kB - 12/12/2017 at 13:01


  • Rev 1.1

    Bharbour02/22/2018 at 18:48 0 comments

    Minimal changes between R1.0 and R1.1, Changed the font width on the pin ID text silkscreen.

  • Verify GPIO Connections

    Bharbour12/21/2017 at 18:29 0 comments

    The last part of checking out this board was to verify that the GPIO pins were connected and routed correctly (to catch schematic or footprint errors) and they are correct. The only real issue found is that the silkscreen printing identifying the PA pins is very hard to read (at least with my eyes). In order to fit the text in place, I used 0.030" text with 0.010 stroke widths. The next board rev will be done with 0.008 stroke width to make the text more readable.

    To do this test, I wrote a simple loop that walks a 1 through a 32 bit wide uint32_t and applies it to the port. Using a scope, I put channel 1 on PA02 (the lowest bit that was not in use for the crystal) and then checked the rest of the PA pins. Watching the timing with the help of the scope cursor, I made sure that the sequence and time relationship worked out to match the expected pin.

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