The Chorus effect generates a delayed signal that is mixed with the original guitar signal. The trick is that the delay is not constant but variable or "modulated".
The variation of the delay time follows a sinusoidal or triangular waveform called LFO (Low-Frequency Oscillator). So, the delay is short and then goes bigger and bigger until it reaches a maximum delay. After that, the delay goes shorter and shorter. This goes in an endless loop operation
This is the complete chorus code:
// CC-by-NC-www.Electrosmash.com/rights
// Based on OpenMusicLabs previous works.
// pedalshield_mega_chorus.ino the ADC read signal is delayed with a triangular LFO and mixed with the clean guitar signal.
// pressing the pushbutton_1 or 2 makes the delay longer or shorter
#include "U8glib.h"
U8GLIB_SH1106_128X64 u8g(U8G_I2C_OPT_NO_ACK); // Display which does not send ACK
//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, output, p, vol_variable=512;
int counter=0;
int count_up=0;
unsigned int ADC_low, ADC_high;
unsigned int max_delay=100;
unsigned int MIN_DELAY=10;
unsigned int DelayBuffer[1000];
unsigned int DelayCounter = 0;
unsigned int Delay_Depth = 100;
unsigned int flanger_speed = 5;
void setup() {
//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; // 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 and write the OLED if the effect is ON.
if (digitalRead(FOOTSWITCH))
{
digitalWrite(LED, HIGH); //light the LED
u8g.firstPage();
do {
u8g.setFont(u8g_font_helvR14r);
u8g.drawStr( 0, 20, " CHORUS ");
u8g.setFont(u8g_font_helvR24r);
u8g.setPrintPos(10, 60);
u8g.print(max_delay);
u8g.setFont(u8g_font_helvR14r);
u8g.setPrintPos(100, 60);
u8g.print(count_up);
} while( u8g.nextPage() );
}
else
{
digitalWrite(LED, LOW); // switch-off the LED
u8g.firstPage();
do {
u8g.setFont(u8g_font_helvR24r);
u8g.drawStr( 0, 32, "EFFECT ");
u8g.drawStr( 0, 64, " OFF ");
} while( u8g.nextPage() );
}
}
ISR(TIMER4_CAPT_vect)
{
// get ADC data
ADC_low = ADCL; // ADC_low always 0 to save space
ADC_high = ADCH;
//store the current reading
DelayBuffer[DelayCounter] = (((ADC_high << 8) | ADC_low) + 0x8000);
counter++; //to save resources, the pushbuttons are checked every 100 times.
if(counter==1000)
{
counter=0;
if (!digitalRead(PUSHBUTTON_2)) if (max_delay<1000)max_delay++; //increase the vol
if (!digitalRead(PUSHBUTTON_1)) if (max_delay>20)max_delay--; //decrease delay
}
DelayCounter++;
if(DelayCounter >= Delay_Depth)
{
DelayCounter = 0;
if(count_up)
{
digitalWrite(LED, HIGH);
for(p=0;p<10;p++)DelayBuffer[Delay_Depth+p]=DelayBuffer[Delay_Depth-1];
Delay_Depth=Delay_Depth+1;
if (Delay_Depth>=max_delay)count_up=0;
}
else
{
digitalWrite(LED, LOW);
Delay_Depth=Delay_Depth-1;
if (Delay_Depth<=MIN_DELAY)count_up=1;
}
}
// output = DelayBuffer[DelayCounter];
output = (DelayBuffer[DelayCounter] + (((ADC_high << 8) | ADC_low) + 0x8000))>>1 ; //chorus
//write the PWM signal
OCR4AL = ((output + 0x8000) >> 8); // convert to unsigned, send out high byte
OCR4BL = output; // send out low byte
}
