ATtiny with USB Boot Loader: Tips & Tricks for DIYers DIYers building a development board similar to this one, and looking for applications to be added through USB without an external programmer, ...

We included the ATTiny85 chip with an on-board USB programmer which simply plugs into the learning kit making it easy to make connections and prototype your projects.

It’s called Micronucleus and it turns the lowly ATtiny 85 into a chip with a USB interface capable of being upgraded via a ‘viral’ uploader program.

For USB serial programming, GGtag uses the Web Serial API through the web interface at ggtag.io. The device can emulate 125 kHz RFID tags through an ATtiny85 MCU and the avrfid firmware.

It offers expanded flash storage, more GPIO, and ditches SPI programming in favor of UPDI — a protocol that can be done using nothing more than an USB-UART converter and a resistor.