Servo - April 2012

FIGURE 8. Recommended hookup for connecting the output of any VLSI VS10xx- based MIDI sound module with an external amplifier. This is from the manufacturer's datasheet. Only one stereo side is shown connected.

set the value. The three most common control change messages – and the ones used in the example sketches – are:

Option Bank Select Channel Volume All Notes Off

Control Byte 0x00 0x07 0x7B

Examples:

0xB0|0  0x00  0x78

0xB0|5  0x07  63

0xB0|3  0x7B  0

// Sets bank 0x78 (decimal
// 120) on channel 0
// Sets volume to 63 on
// channel 5
// Turns off all notes
// playing on channel 3

• Reset. This pin provides a method of resetting the MIDI chip on the sound board to a known state. Do this after the board has been powered up, but before sending any MIDI data. Resetting is accomplished by momentarily bringing the pin LOW, then HIGH again.

Figure 8 shows the basic wiring points between the Arduino and MIDI board. If you’re using a shield, the

Connecting a MIDI Sound Module to the Arduino LISTING 1 - MIDI_VerySimple.ino

// Rx, Tx (Rx not used, Tx pin=3)

Thanks to the “maker movement” there are now a number of affordable MIDI sound modules available for the Arduino and other microcontrollers. Figure 6 shows a MIDI sound module shield from SparkFun, designed for the Arduino Uno (and compatible) development board.

Variations include shields that combine MIDI with MP3 playback, as well as breakout boards that provide additional connection pins for more advanced hookups. Figure 7 shows both of these styles (also from SparkFun). The MIDI/MP3 shield includes an onboard micro-SD card reader that provides storage for the sound files.

Despite all the pins on these boards, most modules require only a couple of connections for MIDI operation:

void setup() {
  MIDI.begin(31250);
  resetMidi(4);
  ctrlMIDI(0, 0x07, 127);
  ctrlMIDI(0, 0x00, 0x79);
  sendMIDI(0xC0|0, 0, 0);
}
// Set up serial comm to MIDI
// Reset MIDI device (pin 8)
// Set channel volume (0-127) to full
// Select 'melodic' bank
// Select instrument in bank
void loop() {
  noteOn(0, 60, 127);
  delay(1000);
  noteOff(0, 60,  127);
  delay(1000);
}
// Turn on middle-C note, velocity=127
// Wait one second
// Turn off note
// Turn note on (press key)
void noteOn(byte channel, byte note, byte attackVelo) {
  sendMIDI( (0x90 | channel), note, attackVelo);
}
// Turn note off (release key)
void noteOff(byte channel, byte note, byte releaseVelo) {
  sendMIDI( (0x80 | channel), note, releaseVelo);
}
// Set controller value with channel
void ctrlMIDI(byte channel, byte data1, byte data2) {
  sendMIDI( (0xB0 | channel), data1, data2);
}
// Send bytes to MIDI device
void sendMIDI(byte cmd, byte data1, byte data2) {
  MIDI.write(cmd);
  MIDI.write(data1);
  // Pass only if valid 2nd byte
  if( (cmd & 0xF0) <= 0xB0 || (cmd & 0xF0) == 0xE0 )
 MIDI.write(data2);

• MIDI input. This pin accepts asynchronous serial at a specific baud rate of 31250 bits per second. Use the Arduino SoftwareSerial object library to transmit serial data directly to the board.

}
// Reset MIDI device
void resetMidi(int resetPin) {
  pinMode(resetPin, OUTPUT);
  digitalWrite(resetPin, LOW);
  delay(100);
  digitalWrite(resetPin, HIGH);
  delay(100);