Arduino-Pedal-Effects/c/variable_pitch_shift.ino

// RING BUFFER VARIABLE PITCH SHIFT
// via www.Electrosmash.com
// via OpenMusicLabs

//defining hardware resources.
#define LED 13
#define FOOTSWITCH 12
#define TOGGLE 2
#define PUSHBUTTON_1 A5
#define PUSHBUTTON_2 A4

//defining the output PWM parameters
#define PWM_FREQ 0x00FF // pwm frequency - 31.3KHz
#define PWM_MODE 0 // Fast (1) or Phase Correct (0)
#define PWM_QTY 2 // 2 PWMs in parallel
#define BUFF_SIZE 500 // size of ring buffer, can theoretically be anything
                      // 500 should hold 15.9 ms of audio
                      //

// STRUCTURES

struct button_time_s
{
  long footswitch;
  long pb1;
  long pb2;
};

struct count_s
{
  int main;
  int interrupt;
};

struct switch_flag_s
{
  bool current;
  bool old;
};

struct ring_buff_s
{
  int buff[BUFF_SIZE];
  int head;
  int tail;
};

struct tempo_s
{
  int interval;
  long timeout;
};

struct divider_s
{
  int input;
  int output;
};

// VARIABLES
int input, vol_variable=512;
byte ADC_low, ADC_high;
bool led_flag;
int offset = 5;
long milli;
button_time_s button_time;
count_s count;
switch_flag_s switch_flag;
ring_buff_s buf;
divider_s divider;
tempo_s tempo;

// BUFFER FUNCTIONS
void push_to_buff(int in)
{
  buf.buff[buf.head] = in;
  buf.head++;
  if (buf.head == BUFF_SIZE)
  {
    buf.head = 0;
  }
}

int pop_from_buff (void)
{
  int out = buf.buff[buf.tail];
  if (buf.tail != buf.head)
  {
    buf.tail++;
  }
  else
  {
    buf.buff[buf.tail]--;
  }
  if (buf.tail == BUFF_SIZE)
  {
    buf.tail = 0;
  }
  return out;
}

void setup()
{
  //setup IO
  Serial.begin(9600);
  pinMode(FOOTSWITCH, INPUT_PULLUP);
  pinMode(PUSHBUTTON_1, INPUT_PULLUP);
  pinMode(PUSHBUTTON_2, INPUT_PULLUP);
  pinMode(LED, OUTPUT);

  // setup ADC
  ADMUX = 0x60; // left adjust, adc0, internal vcc
  ADCSRA = 0xe5; // turn on adc, ck/32, auto trigger
  ADCSRB = 0x07; // t1 capture for trigger
  DIDR0 = 0x01; // turn off digital inputs for adc0

  // setup PWM
  TCCR1A = (((PWM_QTY - 1) << 5) | 0x80 | (PWM_MODE << 1)); //
  TCCR1B = ((PWM_MODE << 3) | 0x11); // ck/1
  TIMSK1 = 0x20; // interrupt on capture interrupt
  ICR1H = (PWM_FREQ >> 8);
  ICR1L = (PWM_FREQ & 0xff);
  DDRB |= ((PWM_QTY << 1) | 0x02); // turn on outputs
  sei(); // turn on interrupts - not really necessary with arduino
  tempo.interval = 150;
  divider.input = 0;
  divider.output = 9;
}

void tempo_setter()
{
  if (milli > tempo.timeout)
  {
    led_flag = !led_flag;
    digitalWrite(LED, led_flag);
    tempo.timeout = milli + tempo.interval;
  }
}

void tempo_getter()
{
  if (digitalRead(PUSHBUTTON_1) == false)
  {
    if (milli > button_time.pb1)
    {
      if (milli - button_time.pb1 > 150)
      {
        tempo.interval = milli - button_time.pb1;
        tempo.timeout = milli + tempo.interval;
      }
      button_time.pb1 = milli;
    }
  }
}

void pitch_getter()
{
  if (digitalRead(PUSHBUTTON_2) == false)
  {
    if (milli - button_time.pb2 > 150)
    {
      divider.output++;
      if (divider.output > 15)
      {
        divider.output = 0;
      }
      if (divider.output == 1)
      {
        divider.output = 2;
      }
      button_time.pb2 = milli;
    }
  }
}

// MAIN LOOP
// checks the footswitch is pushed every 100 loops
// changes the switch_flag
// if switch flag is true call functions
// else just set LED here,
// doesn't need to optimised if no audio is being processed
// increment count

void loop()
{
  if (count.main % 100 == 0)
  {
    switch_flag.current = digitalRead(FOOTSWITCH);
    if (switch_flag.current != switch_flag.old)
    {
      button_time.footswitch = millis();
      digitalWrite(LED, true);
      Serial.println(button_time.footswitch);
    }
    switch_flag.old = switch_flag.current;
    if (switch_flag.current == true)
    {
        milli = millis();
        pitch_getter();
        tempo_getter();
        tempo_setter();
    }
    else
    {
      digitalWrite(LED, false);
    }
  }
  count.main++;
}

// AUDIO INPUT
// pulls the audio from the ADC
// pushes it to the ring buffer
void audio_inputter(int divide)
{
  ADC_low = ADCL; // you need to fetch the low byte first
  ADC_high = ADCH;
  input = ((ADC_high << 8) | ADC_low); // make a signed 16b value
  if (input > 0x8000)
  {
    input = input + 0x8000;
  }
  push_to_buff(input);
}

// AUDIO OUTPUTTER
// if the eqn is != 0
// pop audio from ring buffer and output to PWM
void audio_outputter(int divide)
{
  if (milli - button_time.footswitch > offset)
  {
//    Serial.println("YE");
    if (count.interrupt % divide != 0)
    {
      int output = pop_from_buff();
      OCR1AL = ((output + 0x8000) >> 8); // convert to unsigned, send out high byte
      OCR1BL = output; // send out low byt
    }
  }
}


// TIMER1 INTERRUPT
// checks the switch flag is true
// if LED flag is true, apply effect
// else do not apply effect
ISR(TIMER1_CAPT_vect)
{
  if (switch_flag.current == true)
  {
    if (led_flag == true)
    {
      audio_inputter(divider.input);
      audio_outputter(divider.output);
    }
    else
    {
      audio_inputter(0);
      audio_outputter(0);
    }
    count.interrupt++;
  }
}