Author says: “Over the summer I needed to find a way to get OFF of the arduino board and onto smaller/cheaper microcontrollers for more permanent projects.
For a while I have been using the ArduinoISP sketch to upload files, but if I wanted to upload a hex file, I needed a real programmer. So I looked at adafruit’s USBTinyISP, which I must say, was VERY cheap comparing to Atmel’s other programmers. As cheap as it was, it was $22; I don’t spend $22 on one thing, so, let me get started on how to make your own usbtinyisp.”