• MIDI Specification - good article about the MIDI protocol
• simple_midi_specification - Midi in Hex for editors of .ini files
• http://www.zem-college.de/midi/index.htm - MIDI Specification (German)

• http://www.esacademy.com/faq/i2c/index.htm - General I2C FAQ (English)
• http://www.nxp.com/acrobat/literature/9398/39340011.pdf - Original-Specifikation NXP Semiconductors V2.1 (English)
• http://www.nxp.com/acrobat_download/usermanuals/UM10204_3.pdf - Original-Specifikation NXP Semiconductors V03 (English)

Official STM32F4 Page

• DIY MIDI Controllers Using PIC Microcontrollers and BASIC Stamps - lots of little projects with code about manipulating and handling MIDI
• PICList - Plenty of PIC code and inspiration here!

• Encyclopedia Entries
• Circuit Designs - Various circuit resources that have things that could be implemented in Midibox