This was a small project to test the V-USB stack on an ATtiny85 microcontroller. Needing something "useful" to control, I chose two NeoPixel LEDS that are connected in series.

There is no schematics because I wired everything on a piece of protoboard .. even the USB connector itself is a sketchy result of sanding down four large solder bridges. I definitely wouldn't recommend this approach if you like your host's USB bus but it works for me™.

I'm using the micronucleus bootloader here. The initial flash must happen with clips or by using a dedicated programmer socket for the ATtiny85. After you've verified that the bootloader works and can speak to your host via USB, you can flash programs simply by re-plugging the usbpixel.

The bootloader/ directory contains a configuration that must be linked or copied into a checked out micronucleus repository.

cd $MICRONUCLEUS/firmware/
ln -s $USBPIXEL/bootloader configuration/usbpixel
make CONFIG=usbpixel

The firmware is a PlatformIO project. Simply build and upload the firmware with pio – the tool will block and wait until it sees a micronucleus device on the USB bus. The bootloader above is configured to always enter the bootloader on boot, so you just need to re-plug the usbpixel into your USB port.

Note: You may need to fix the micronucleus tool used by PlatformIO first, see platformio/platform-atmelavr#101.

cd $USBPIXEL/firmware
pio run -t upload

In order to interface with the usbpixel I've written a small tool using Google's google/gousb, which wraps libusb. It is a pretty minimal example showing how easy it is to use the different control messages.

cd $USBPIXEL/cli
go build -o usbpixel

Check the -help command for available commands.

./usbpixel -help