nullr0ute's blog

One of my little maker projects has a need for a battery powered micro controller, some DIY to clean up some old equipment and some basic HW design. Ultimately I’d like to be able to integrate it as a fun thing into home automation possibly even using Matter. More on the project for another post.

To move things forward and actually be able to play with LEDs and buttons rather than doing a board port I decided to use the standard firmware. I looked through my collection of micro controllers and found a FeatherS2, it’s based on the ESP-32-S2 MCU with WiFi in a Adafruit Feather form factor with builtin LiPo charger circuit, a USB-C interface, an onboard RGB LED and runs CircuitPython.

Next up I needed to get a development environment up and running on Fedora, batteries and other HW bits can come later. First step was to work out how to getting it running the latest CircuitPython. On the CircuitPython page for the FeatherS2 there’s two firmware, one for boot and USB and then CircuitPython itself.

Step one: Ensure you’re in the dialout group
A lot of micro contollers use serial ports to interface with so you need to be able to talk to a variety of them such as ttyACM0, ttyUSB0 or ttyS0. Simplest way to do this is to add yourself to the dialout group as follows:

sudo usermod -aG dialout ${USER}

Step two: Upgrade UF2 Bootloader
This step was probably unneeded but I upgraded to the 0.11.0 release to ensure I had all the latest fixes. For this bit you need to put the board into recovery. There’s two buttons, you plug it in, press and hold BOOT, press and release RST (reset) and then a second later release BOOT. You can then run the following commands to upgrade UF2:

sudo dnf install -y esptool unzip wget
mkdir ~/CircuitPython; cd ~/CircuitPython
wget https://github.com/adafruit/tinyuf2/releases/download/0.11.0/tinyuf2-unexpectedmaker_feathers2-0.11.0.zip
unzip tinyuf2-unexpectedmaker_feathers2-0.11.0.zip
esptool.py -p /dev/ttyACM0 write_flash 0x0 combined.bin

Once the flash completes you press the RST button and the board will got into a UF2 download mode with the RGB shining a bright green. You’ll also find you have a new USB drive appear with the name of UFTHRS2BOOT. Next step is CircuitPython!

Step three: Install CircuitPython
The latest stable release when I started playing with this was 7.3.3. To install is a simple copy of the uf2 file. While it’s copying the RGB will flash orange, once complete the board will reset and reboot into CircuitPython:

cd ~/CircuitPython
wget https://downloads.circuitpython.org/bin/unexpectedmaker_feathers2/en_GB/adafruit-circuitpython-unexpectedmaker_feathers2-en_GB-7.3.3.uf2
cp adafruit-circuitpython-unexpectedmaker_feathers2-en_GB-7.3.3.uf2 /run/media/${USER}/UFTHRS2BOOT/

Step three: Actually make it do something
The standard development environment for MicroPython and/or CircuitPython is an IDE called MU Editor. It’s nicely packaged up in Fedora and seems to just work. The code in CircuitPython appears in a /run/media/${USER}/CIRCUITPY/ drive which mu automatically detects and you can get access to the python console directly within MU (correct permissions via the dialout group in step one). By default the FeatherS2 has a little app that cycles through colours on the RGB.

sudo dnf install -y mu

Next steps
The CircuitPython firmware has lots of built in functionality that just works, there’s also a large ecosystem of libraries and drivers available for Micropython and CircuitPython. Adafruit have a lot of extremely good tutorials to get you going. Next up I plan to play with getting it on my IoT network using WiFi and communicating via MQTT.