This troubleshooting tool communicates between a PC and any embedded device over most standard serial protocols and a range of 0-5.5VDC. It's a tremendous help when reverse engineering, troubleshooting, observing new hardware, and/or when needing to generate a test signal.
The Bus Pirate, created by Ian Lesnet and featured on Hack a Day, has a simple and effective operation - type commands into a terminal on your computer, and those commands are interpreted by the Bus Pirate and sent via the proper protocol. The Pirate will also interpret data sent from your embedded device back to your computer terminal. A big bonus is the bootloader installed on the PIC, which allows you to easily update the firmware and change the functionality of the board.
To quickly use the Bus pirate just open up your favorite serial terminal program (such as Hyperterminal) and follow the instructions found at the User Interface page.
The main components of the Bus Pirate are PIC24FJ64 processor and an FT232RL USB-to-Serial chip. A Mini-B USB connector is populated on the board, and when you plug it into your computer it will come up as a virtual COM port. The pinout of the 2x5 I/O header is documented here. The Bus Pirate is designed to be used with the 10-pin breakout Cable and IC hooks with pigtails.