We used a Microchip PIC24FJ64GA002 28pin SOIC microcontroller (IC1) in this project. The power pins have 0.1uF bypass capacitors to ground (C1,2). The 2.5volt internal regulator requires a 10uF tantalum capacitor (C20). The chip is programmed through a five pin header (ICSP). A 2K pull-up resistor (R1) is required for the MCLR function on pin 1. Read more about this chip in our PIC24F introduction.
An inexpensive MAX3232CSE RS232 transceiver (IC2) interfaces the PIC to a PC serial port. This chip replaces the expensive through-hole MAX3223EEPP+ used in the previous version of the Bus Pirate. The serial interface will work with a USB->serial adapter.