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:
Tiny AVR Programmer Hookup Guide
A how-to on the Tiny AVR Programmer. How to install drivers, hook it up, and program your favorite Tiny AVRs using AVRDUDE!
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.
Qwiic Quad Relay Hookup Guide
SparkFun’s Qwiic Quad Relay is a product designed for switching not one but four high powered devices from your Arduino or other low powered microcontroller using I2C.