Arduino-Pedal-Effects/c/tremolo.ino

// CC-by-www.Electrosmash.com
// Based on OpenMusicLabs previous works.
// pedalshield_uno_tremolo.ino creates a tremolo effect, modulating the volume with a sinewave.
// pressing the pushbutton_1 or 2 makes the modulation faster or slower.

//this waveform is used to modulate the volume of the output signal.
const byte waveform[]=
{
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0x1,0x1,0x0,0x0,
};

//defining harware 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

//other variables
int input, speed=1;
int counter=0;
unsigned int ADC_low, ADC_high;
int sample=0;
int divider=0;

void setup() {
  //setup IO
  pinMode(TOGGLE, INPUT_PULLUP);
  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
  }

void loop()
{
  //Turn on the LED if the effect is ON.
  if (digitalRead(FOOTSWITCH)) digitalWrite(LED, HIGH);
    else  digitalWrite(LED, LOW);

  //nothing else here, all happens in the Timer 1 interruption.
}

ISR(TIMER1_CAPT_vect)
{
  // get ADC data
  ADC_low = ADCL; // you need to fetch the low byte first
  ADC_high = ADCH;

  // the input signal is modulated here using a sinewave
  ADC_low = map(ADC_low, 0,255, 0, waveform[sample]);
  ADC_high = map(ADC_high, 0,255, 0, waveform[sample]);

  //construct the input sumple summing the ADC low and high byte.
  input = ((ADC_high << 8) | ADC_low) + 0x8000; // make a signed 16b value

  counter++; //to save resources, the pushbuttons are checked every 1000 times.
  if(counter==1000)
{

counter=0;
if (!digitalRead(PUSHBUTTON_2)) {
  if (speed<1024)speed=speed+1; //increase the vol
    digitalWrite(LED, LOW); //blinks the led
    }

    if (!digitalRead(PUSHBUTTON_1)) {
  if (speed>0)speed=speed-1; //decrease vol
  digitalWrite(LED, LOW); //blinks the led
    }
}

  // there is a divider to slow the waveform (otherwise is too fast)
  divider++;
  if (divider==4){ divider=0; sample=sample+speed;}

 if(sample>1023)sample=0;

  //write the PWM signal
  OCR1AL = ((input + 0x8000) >> 8); // convert to unsigned, send out high byte
  OCR1BL = input; // send out low byte
}