uClock/examples/MidiClock/MidiClock.ino

#include "Arduino.h"
#include <uClock.h>

// MIDI clock, start and stop byte definitions - based on MIDI 1.0 Standards.
#define MIDI_CLOCK 0xF8
#define MIDI_START 0xFA
#define MIDI_STOP  0xFC

// The callback function wich will be called by Clock each Pulse of 24PPQN clock resolution.
void onSync24Callback(uint32_t tick) 
{
  // Send MIDI_CLOCK to external gears
  Serial.write(MIDI_CLOCK);
}

// The callback function wich will be called when clock starts by using Clock.start() method.
void onClockStart() 
{
  Serial.write(MIDI_START);
}

// The callback function wich will be called when clock stops by using Clock.stop() method.
void onClockStop() 
{
  Serial.write(MIDI_STOP);
}

void setup() 
{

  // Initialize serial communication at 31250 bits per second, the default MIDI serial speed communication:
  Serial.begin(31250);

  // Inits the clock
  uClock.init();
  // Set the callback function for the clock output to send MIDI Sync message.
  uClock.setOnSync24(onSync24Callback);
  // Set the callback function for MIDI Start and Stop messages.
  uClock.setOnClockStart(onClockStart);  
  uClock.setOnClockStop(onClockStop);
  // Set the clock BPM to 126 BPM
  uClock.setTempo(126);

  // Starts the clock, tick-tac-tick-tac...
  uClock.start();

}

// Do it whatever to interface with Clock.stop(), Clock.start(), Clock.setTempo() and integrate your environment...
void loop() 
{

}