This is a project that is based on Sanguinololu. The ATmega644P has been replaced with an Atmel AT90USB1286 MCU. This Microcontroller has onboard USB, removing the need for the FTDI USB UART. Additionally all of the through hole resistors and capacitors have been replaced with 0805 SMT components(as of REV 0.23) The overall part count is less than the Sanguinololu. Like the Sanguinololu the Teensylu has expansion headers supporting I2C, SPI, UART, ADC pins, and externally mounted LED's. All extra I/O ports have been broken out to headers for prototyping.