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TOPIC: Tremolo Effect Guitar Pedal

Tremolo Effect Guitar Pedal 7 months 4 weeks ago #1268

The tremolo effect produces a variation in the volume of the guitar signal. In this case, the guitar signal is modulated using a sinusoidal waveform which is stored in memory.
Bear in mind this 2 important things:
  • This code is very noisy because the background noise is also modulated with the sinewave. Maybe using another strategy you can have a noisless tremolo effect, but this simple one works like this... sorry :(
  • The OLED is not updated or shows any variable. When using the "map" function, that takes a lot of resources, the OLED will nto work. The Booster pedal has the same problem (it also uses the map function)

This is the complete tremolo code:
// CC-by-www.Electrosmash.com
// Based on OpenMusicLabs previous works.
// pedalshield_mega_tremolo.ino creates a tremolo effect, modulating the volume with a sinewave.
// pressing the pushbutton_1 or 2 makes the modulation faster or slower.
 
#include "U8glib.h"
U8GLIB_SH1106_128X64 u8g(U8G_I2C_OPT_NO_ACK);  // Display which does not send ACK
 
//this waveform is used to modulate the volume of the output signal.
const byte waveform[]=
{
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0x40,0x3f,0x3f,0x3f,0x3e,0x3e,0x3d,0x3d,0x3d,0x3c,0x3c,0x3b,0x3b,0x3b,0x3a,0x3a,0x39,0x39,0x39,0x38,
0x38,0x38,0x37,0x37,0x36,0x36,0x36,0x35,0x35,0x34,0x34,0x34,0x33,0x33,0x32,0x32,0x32,0x31,0x31,0x30,
0x30,0x30,0x2f,0x2f,0x2f,0x2e,0x2e,0x2d,0x2d,0x2d,0x2c,0x2c,0x2b,0x2b,0x2b,0x2a,0x2a,0x29,0x29,0x29,
0x28,0x28,0x27,0x27,0x27,0x26,0x26,0x26,0x25,0x25,0x24,0x24,0x24,0x23,0x23,0x22,0x22,0x22,0x21,0x21,
0x20,0x20,0x20,0x1f,0x1f,0x1e,0x1e,0x1e,0x1d,0x1d,0x1d,0x1c,0x1c,0x1b,0x1b,0x1b,0x1a,0x1a,0x19,0x19,
0x19,0x18,0x18,0x17,0x17,0x17,0x16,0x16,0x16,0x15,0x15,0x14,0x14,0x14,0x13,0x13,0x12,0x12,0x12,0x11,
0x11,0x10,0x10,0x10,0xf,0xf,0xe,0xe,0xe,0xd,0xd,0xd,0xc,0xc,0xb,0xb,0xb,0xa,0xa,0x9,
0x9,0x9,0x8,0x8,0x7,0x7,0x7,0x6,0x6,0x5,0x5,0x5,0x4,0x4,0x4,0x3,0x3,0x2,0x2,0x2,
0x1,0x1,0x0,0x0,
};
 
//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

//other variables
int input, speedy=1;
int counter=0;
unsigned int ADC_low, ADC_high;
int sample=0;
int divider=0;
 
void setup() {
 
   u8g.firstPage(); 
 do {
    u8g.setFont(u8g_font_helvR18r);
    u8g.drawStr( 0, 30, " TREMOLO");    
    u8g.drawStr( 0, 60, "  EFFECT");
    } while( u8g.nextPage() );
 
 
  //setup IO
  pinMode(FOOTSWITCH, INPUT_PULLUP);
  pinMode(TOGGLE, INPUT_PULLUP);
  pinMode(PUSHBUTTON_1, INPUT_PULLUP);
  pinMode(PUSHBUTTON_2, INPUT_PULLUP);
  pinMode(LED, OUTPUT);
  pinMode(6, OUTPUT); //PWM0 as output
  pinMode(7, OUTPUT); //PWM1 as output
 
  // setup ADC
  ADMUX = 0x60; // left adjust, adc0, internal vcc
  ADCSRA = 0xe5; // turn on adc, ck/32, auto trigger
  ADCSRB = 0x00; // ADC free running mode
  DIDR0 = 0x01; // turn off digital inputs for adc0
 
  // setup PWM
  TCCR4A = (((PWM_QTY - 1) << 5) | 0x80 | (PWM_MODE << 1)); //
  TCCR4B = ((PWM_MODE << 3) | 0x11); // ck/1
  TIMSK4 = 0x20; // interrupt on capture interrupt
  ICR4H = (PWM_FREQ >> 8);
  ICR4L = (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);
}
 
ISR(TIMER4_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 (speedy<1024)speedy=speedy+1; //increase the vol
    digitalWrite(LED, LOW); //blinks the led
    }
 
    if (!digitalRead(PUSHBUTTON_1)) {
  if (speedy>0)speedy=speedy-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+speedy;}
 
 if(sample>1023)sample=0;
 
  //write the PWM signal
   OCR4AL = ((input + 0x8000) >> 8); // convert to unsigned, send out high byte
   OCR4BL = input; // send out low byte
}
 
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