“In this tutorial, we’ll show you how to use Arduino to install the micronucleus bootloader, which has V-USB, onto an ATtiny84. These steps will work for other ATtiny chips, but you’ll need to change things like the pins_arduino.h file and target parameters in avrdude. By following this guide, you will be able to upload Arduino sketches directly to the ATtiny84 over USB without needing to use a programming device (such as another Arduino or FTDI chip). The Atmel AVR ATtiny84 is very similar to the ATtiny85 but with a few more I/O pins (six more, to be exact). If you like working with very small, inexpensive microcontrollers, the ATtiny84 and lower-power ATtiny84A are good options. Either the ATtiny84 or ATtiny84A will work for this tutorial.”