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Greenpill - a SAMD51 development board 2020-08-03

I designed a microcontroller board! You can see the board files here on GitHub! That's about it.

As for how this board came to be - a friend designed a keyboard project around a cheap STM32 board from AliExpress as the controller. It turned out to have some issues using it with CircuitPython, namely that the USB was not flexible enough to have HID, MSC and CDC active at the same time. The SAMD51 should be able to achieve this, though.

One bare board on the table. One assembled board on the table.

(yes that has a ton of flux residue on it, shh)

The only issue I ran into was that the Typical Application Circuit in the datasheet for the 3.3v regulator I used was slightly misleading - it has EN floating, whereas EN is active high, so should be tied to VIN (in my case) for it to work.

Typical Application Circuit from MIC5504 datasheet

At the start of the datasheet it states that

The MIC5503 and MIC5504 have an internal pull-down resistor on the enable pin that disables the output when the enable pin is left floating.

so really it's my fault for not reading the datasheet carefully enough.
Luckily it can be fixed with just a wire connecting pins 1/3 of the regulator, which you can see in the photo above.

I plan on porting both the Arduino framework as well as CircuitPython, and will be using the Adafruit SAMD bootloader for USB flashing. Watch this space!