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The folks over at Hack a Day have gone into the electronic components biz. Teaming up with Seeed Studio, they're producing the Bus Pirate. The Bus Pirate is a universal serial bus tool. Use it for understanding how components work before you build a full prototype. Their parts posts page shows many example uses. Here's more about the board:

The Bus Pirate is a universal bus interface that talks to most chips from a PC serial terminal, eliminating a ton of early prototyping effort when working with new or unknown chips. Many serial protocols are supported at 0.6-5.5volts, more can be added.

* 1-Wire
* I2C
* SPI
* JTAG
* Asynchronous serial
* MIDI
* PC keyboard
* 2- and 3-wire libraries with bitwise pin control

We added other stuff we need, like,

* 0-6volt measurement probe
* 1hz-40MHz frequency measurement
* 1kHz - 4MHz pulse-width modulator, frequency generator
* On-board multi-voltage pull-up resistors
* On-board 3.3volt and 5volt power supplies with software reset
* Macros for common operations
* Bus traffic sniffer (SPI)
* A bootloader for easy firmware updates

Since this has been such a useful tool for us, we cleaned up the code, documented the design, and released it here with specs, schematic, and source code.

The Bus is available for pre-orders and sells for $27.15.

Bus Pirate preorders open
How-to: The Bus Pirate V2 with USB
The Bus Pirate universal serial interface