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This example is for Wiring version 1.0 build 0100+. If you have a previous version, use the examples included with your software. If you see any errors or have comments, please let us know.

MIDI note player by Tom Igoe
This sketch shows how to use the serial transmit pin (pin 33) to send MIDI note data. If this circuit is connected to a MIDI synth, it will play the notes F#-0 (0x1E) to F#-5 (0x5A) in sequence. The circuit: Serial RX (pin 33 on Wiring v1 boards or pin 1 on Wiring S) connected to MIDI jack pin 5 MIDI jack pin 2 connected to ground MIDI jack pin 4 connected to +5V through 220-ohm resistor Attach a MIDI cable to the jack, then to a MIDI synth, and play music. http://www.arduino.cc/en/Tutorial/MIDI

    void setup()
    {
      // Set MIDI baud rate:
      Serial.begin(31250);
    }

    void loop()
    {
      // play notes from F#-0 (0x1E) to F#-5 (0x5A):
      for (int note = 0x1E; note < 0x5A; note ++)
      {
        //Note on channel 1 (0x90), some note value (note), middle velocity (0x45):
        noteOn(0x90, note, 0x45);
        delay(100);
        //Note on channel 1 (0x90), some note value (note), silent velocity (0x00):
        noteOn(0x90, note, 0x00);
        delay(100);
      }
    }

    //  plays a MIDI note.  Doesn't check to see that
    //  cmd is greater than 127, or that data values are  less than 127:
    void noteOn(int cmd, int pitch, int velocity)
    {
      Serial.write(cmd);
      Serial.write(pitch);
      Serial.write(velocity);
    }