A Custom AVR128DA32 Feather Board
David Johnson-Davies designed his own Microchip AVR128DA32 board in Adafruit's Feather form factor.
As David Johnson-Davies explains in his latest Technoblogy post, Adafruit’s Feather format is one of his favorite board form factors. However, the Microchip AVR128DA microcontroller, one of his favorite microcontrollers, wasn’t available as a Feather board. So he created his own!
Measuring 0.9 x 2.0”, the Feather is small enough to fit on a breadboard, while large enough for a sufficient array of IO pins. Since Adafruit published the Feather standard, DJD was able to easily integrate the AVR128DA into this footprint, giving him a starting point and access to FeatherWing add-on modules. The AVR128DA chip features 128KB of flash and 16KB of RAM, making the new board ideal for running his uLisp interpreter.
DJD fulfilled the standard Feather specifications, such as a JST LiPo connector, reset button, 3.3V logic, six analog pins, and seven GPIO pins. He also added a microSD card socket (for saving Lisp programs and data), a mini NeoPixel, and an analog pin connected to VBAT via a voltage divider for battery monitoring. The circuit diagram is provided in the writeup, and the design files are available on GitHub if you want to duplicate and/or examine his board.
DJD also outlines how to install a bootloader on the AVR128DA28, allowing users to upload programs from the Arduino IDE, and presents an enhanced blinky sketch for testing. This outputs “SOS” in Morse Code instead of the standard repeating (and, one might argue, sort of boring) on/off sequence. Finally, he goes over using the uLisp interpreter, and even outlines how to integrate assembly code into your routine.
The AVR128DA32 Feather looks like a lot of fun. It’s also a great reminder to consider if you can use an existing board format, rather than starting something entirely from scratch!