A tight BPM clock generator for Arduino
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README.md

uClock

BPM clock generator for Arduino is a library to implement BPM clock tick calls using hardware timer1 interruption for tight and solid timming clock ticks. Tested on ATmega168/328, ATmega16u4/32u4 and ATmega2560.

Generate your self tight BPM clock for music, audio/video productions, performances or instalations. You can clock your MIDI setup or sync different protocols as you wish.

Interface

Clock library interfaces via attached callback function running on a hardware interrupt and is able to process the following resolutions:

  1. 16PPQN 16 Pulses Per Quarter Note
  2. 32PPQN 32 Pulses Per Quarter Note
  3. 96PPQN 96 Pulses Per Quarter Note

To generate a MIDI sync signal to sync external MIDI devices for example, you need to work with the resolution of 96PPQN to follow the standards of MIDI protocol that handles the clock based on 24PPQN.

For a simple old felling step sequencer a 16PPQN resolution is a good way to start coding your own step sequencer.

You can also use all the 3 resolutions at the same time for whatever reason you think you should.

Examples

Here a few examples on the usage of Clock library for MIDI devices, keep in mind the need to make your own MIDI interface, more details will be avaliable soon but until that, you can find good material over the net about the subject.

If you dont want to build a MIDI interface and you are going to use your arduino only with your PC, you can use a Serial-to-Midi bridge and connects your arduino via USB cable to your conputer to use it as a MIDI tool like this one.

A Simple MIDI Sync Box sketch example

Here is a example on how to create a simple MIDI Sync Box

#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 96PPQN clock resolution.
void ClockOut96PPQN(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.setClock96PPQNOutput(ClockOut96PPQN);
  // Set the callback function for MIDI Start and Stop messages.
  uClock.setOnClockStartOutput(onClockStart);  
  uClock.setOnClockStopOutput(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() {

}

Acid Step Sequencer

A clone of Roland TB303 step sequencer main engine, here is a example with no user interface for interaction. If you're looking for a user interactable TB303 sequencer engine clone with user interface please take a look here https://github.com/midilab/uClock/tree/master/examples/AcidStepSequencer.

// Roland TB303 Step Sequencer engine clone.
// No interface here, just the engine as example.
// author: midilab contact@midilab.co
// Under MIT license
#include "Arduino.h"
#include <uClock.h>

// Sequencer config
#define STEP_MAX_SIZE      16
#define NOTE_LENGTH        4 // min: 1 max: 5 DO NOT EDIT BEYOND!!!
#define NOTE_VELOCITY      90
#define ACCENT_VELOCITY    127

// MIDI config
#define MIDI_CHANNEL      0 // 0 = channel 1

// do not edit below!
#define NOTE_STACK_SIZE    3

// MIDI clock, start, stop, note on and note off byte definitions - based on MIDI 1.0 Standards.
#define MIDI_CLOCK 0xF8
#define MIDI_START 0xFA
#define MIDI_STOP  0xFC
#define NOTE_ON    0x90
#define NOTE_OFF   0x80

// Sequencer data
typedef struct
{
  uint8_t note;
  bool accent;
  bool glide;
  bool rest;
} SEQUENCER_STEP_DATA;

typedef struct
{
  uint8_t note;
  int8_t length;
} STACK_NOTE_DATA;

// main sequencer data
SEQUENCER_STEP_DATA _sequencer[STEP_MAX_SIZE];
STACK_NOTE_DATA _note_stack[NOTE_STACK_SIZE];
uint16_t _step_length = STEP_MAX_SIZE;

// make sure all above sequencer data are modified atomicly only
// eg. ATOMIC(_sequencer[0].accent = true); ATOMIC(_step_length = 7);
uint8_t _tmpSREG;
#define ATOMIC(X) _tmpSREG = SREG; cli(); X; SREG = _tmpSREG;

// shared data to be used for user interface feedback
bool _playing = false;
uint16_t _step = 0;

void sendMidiMessage(uint8_t command, uint8_t byte1, uint8_t byte2)
{ 
  // send midi message
  command = command | (uint8_t)MIDI_CHANNEL;
  Serial.write(command);
  Serial.write(byte1);
  Serial.write(byte2);
}

// The callback function wich will be called by uClock each Pulse of 16PPQN clock resolution. Each call represents exactly one step.
void ClockOut16PPQN(uint32_t * tick) 
{
  uint16_t step;
  uint16_t length = NOTE_LENGTH;
  
  // get actual step.
  _step = *tick % _step_length;
  
  // send note on only if this step are not in rest mode
  if ( _sequencer[_step].rest == false ) {

    // check for glide event ahead of _step
    step = _step;
    for ( uint16_t i = 1; i < _step_length; i++  ) {
      ++step;
      step = step % _step_length;
      if ( _sequencer[step].glide == true && _sequencer[step].rest == false ) {
        length = NOTE_LENGTH + (i * 6);
        break;
      } else if ( _sequencer[step].rest == false ) {
        break;
      }
    }

    // find a free note stack to fit in
    for ( uint8_t i = 0; i < NOTE_STACK_SIZE; i++ ) {
      if ( _note_stack[i].length == -1 ) {
        _note_stack[i].note = _sequencer[_step].note;
        _note_stack[i].length = length;
        // send note on
        sendMidiMessage(NOTE_ON, _sequencer[_step].note, _sequencer[_step].accent ? ACCENT_VELOCITY : NOTE_VELOCITY);    
        return;
      }
    }
  }  
}

// The callback function wich will be called by uClock each Pulse of 96PPQN clock resolution.
void ClockOut96PPQN(uint32_t * tick) 
{
  // Send MIDI_CLOCK to external hardware
  Serial.write(MIDI_CLOCK);

  // handle note on stack
  for ( uint8_t i = 0; i < NOTE_STACK_SIZE; i++ ) {
    if ( _note_stack[i].length != -1 ) {
      --_note_stack[i].length;
      if ( _note_stack[i].length == 0 ) {
        sendMidiMessage(NOTE_OFF, _note_stack[i].note, 0);
        _note_stack[i].length = -1;
      }
    }  
  }
}

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

// The callback function wich will be called when clock stops by using Clock.stop() method.
void onClockStop() 
{
  Serial.write(MIDI_STOP);
  // send all note off on sequencer stop
  for ( uint8_t i = 0; i < NOTE_STACK_SIZE; i++ ) {
    sendMidiMessage(NOTE_OFF, _note_stack[i].note, 0);
    _note_stack[i].length = -1;
  }
  _playing = false;
}

void setup() 
{
  // Initialize serial communication
  // the default MIDI serial speed communication at 31250 bits per second
  Serial.begin(31250); 

  // Inits the clock
  uClock.init();
  
  // Set the callback function for the clock output to send MIDI Sync message.
  uClock.setClock96PPQNOutput(ClockOut96PPQN);
  
  // Set the callback function for the step sequencer on 16ppqn
  uClock.setClock16PPQNOutput(ClockOut16PPQN);  
  
  // Set the callback function for MIDI Start and Stop messages.
  uClock.setOnClockStartOutput(onClockStart);  
  uClock.setOnClockStopOutput(onClockStop);
  
  // Set the clock BPM to 126 BPM
  uClock.setTempo(126);

  // initing sequencer data
  for ( uint16_t i = 0; i < STEP_MAX_SIZE; i++ ) {
    _sequencer[i].note = 48;
    _sequencer[i].accent = false;
    _sequencer[i].glide = false;
    _sequencer[i].rest = false;
  }

  // initing note stack data
  for ( uint8_t i = 0; i < NOTE_STACK_SIZE; i++ ) {
    _note_stack[i].note = 0;
    _note_stack[i].length = -1;
  }

  // pins, buttons, leds and pots config
  //configureYourUserInterface();
  
  // start sequencer
  uClock.start();
}

// User interaction goes here
void loop() 
{
  // Controls your 303 engine interacting with user here...
  // you can change data by using _sequencer[] and _step_length only! do not mess with _note_stack[]!
  // IMPORTANT!!! Sequencer main data are used inside a interrupt enabled by uClock for BPM clock timing. Make sure all sequencer data are modified atomicly using this macro ATOMIC();
  // eg. ATOMIC(_sequencer[0].accent = true); ATOMIC(_step_length = 7);
  //processYourButtons();
  //processYourLeds();
  //processYourPots();
}