How to Install an ATtiny Bootloader With Virtual USB
Contributors:
Shawn Hymel
Shawn Hymel 
Resources and Going Further
While this is a lot of information to take in, it shows how to hack the Arduino IDE to load custom board definitions. These steps should work for other ATtiny devices that are supported by the micronucleus project, such as:
You might have to modify the pins_arduino.h file, however, if you plan to use a different ATtiny.
ATtiny84 Pinout
If you need additional support, please check out the following resources.
If you want to go further with the ATtiny, please check out our additional tutorials that showcase the ATtiny:
Pocket AVR Programmer Hookup Guide
Skip the bootloader and load your program directly onto an AVR with the AVR Pocket Programmer.
Installing a Bootloader on the MicroView
Fix your bootloader-less MicroView! This tutorial covers how to: disassemble the MicroView, wire it up to an assortment of programmers, program the bootloader, and test it out.
Hack Your Roshamglo Badge
Learn how to customize and program your Roshamglo badge.
Pi AVR Programmer HAT Hookup Guide
In this tutorial, we will use a Raspberry Pi 3 and the Pi AVR Programmer HAT to program an ATMega328P target. We are going to first program the Arduino bootloader over SPI, and then upload an Arduino sketch over a USB serial COM port.