Making a MIDI Keyboard

1
Making a MIDI Keyboard

• Bob Wayne Bell, Jr.
• Nov. 15, 2002
• EE281

2
Introduction to MIDI

• MIDI is the acronym for Musical Instrument
  Digital Interface.
• The MIDI protocol allows electronic devices
  (usually synthesizers, but also computers, light
  show controllers, VCRs, multi-track recorders,
  etc.) to interact and work in synchronization
  with other MIDI compatible devices.
• Using a master controller device such as a
  keyboard, one can play or trigger sounds from
  other electronic devices remotely.

3
Introduction to Project

• MIDI keyboard connects to computer sound card or
  synthesizer module to create MIDI code.
• This Project is built around the 8031
  microcontroller.
• Once keyboard circuit diagram is drawn out, one
  can construct scanning circuitry that
  continuously loops through a test of each key to
  see if it is open or closed.

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The Bare Keyboard

• One must acquire a bare musical keyboard
• Each key (on recent keyboards) will have at least
  two switches for velocity sensitivity.
• Essential to map out the circuitry built into the
  keyboard because the MIDI interface must be built
  around this.

5
Circuit Design

• Microcontroller
• Memory
• Keyboard/switch interface
• MIDI/RS232 interface
• Power supply

6
Circuit Schematic
7
Software Algorithm

• The software loops through a check of each 1st
  switch for every key.
• If it finds that switch 1 is open it checks to
  see if it was open the last time it looked. If
  this is the case it continues scanning.
• If it finds that it is open but was closed the
  last time it looked then it stores info that it
  is now open and then sends the "note off value"
  for that key out the midi port.

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Software Algorithm Contd

• If it finds that switch 1 is closed then it
  checks to see if switch 2 for that key is open.
• If it is open then it increments the velocity
  register value and continues the scan. If it
  finds that switch 2 is closed then it checks a
  register to see if that note is already on. If so
  then it continues the scan.
• If not then it sends the "note on value for that
  key out the midi port and also sends a velocity
  value from the velocity table that is incremented
  for each keycheck loop. Therefore, the more times
  that the software loops the lower the velocity
  value sent.

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Keyboard to Sound Cable
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More references

• General MIDI information
• http//www.midi.com/
• Making a MIDI keyboard
• http//home.insightbb.com/tomatwell/midi/midi_ke
  y_intro.html