This is a monodirectional MIDI to RS232 (serial) interface, it play only MIDI to personal PC “RS232″. The MIDI output connector indicated on the left picture  dosen’t work because the buffer inside pic16f84 is too short. source

The Linuxstamp is designed to be a general purpose processor module. It is designed to work as a stand alone module (SD card, Ethernet and USB/Serial converter are all on the module). This allows all initial development to be done without a motherboard, but for integration into a specific project a motherboard with specific features could be designed. source

A simple RS232 example project that takes all the power it needs from the serial port. Use it to power your microcontroller and communicate between serial port and microcontroller. Takes advantage of the fact that pc serial ports will accept 0-5V rather than the RS232 standard of around negative 10V to positive 10V. Very convenient – no external power required! Note that you may use either a 5.1V zener or a 5V source

A two-chip circuit which connects to the parallel printer port of an IBM PC or compatible computer provides 16 TTL-compatible i/o lines which are programmable in 4 groups of 4 bits. A short program in Turbo Pascal is given as an example of how to program the interface. The circuit can be expanded at the cost of one additional chip per 16 i/o bits.source

The purpose of this project was to create a useful yet easy to build Logic Analyzer that would provide much of the functionality of a real Logic Analyzer. The biggest drawback that the computer has is its sampling rate. The program was written on a 75 MHz Pentium computer which provided accurate sampling rates up to 10 kHz. Although this doesn’t match the speed of real Logic Analyzers, this should be sufficient speed to be useful for many projects. source