User:Fabien Labeyrie/Clapping Arduino Modulo

Clapping Arduino

The following exercise puts Steve Reich into an italian chip, using its tone functionality. As a result, it should be able to play the clapping music by itself.

Version I : two speakers and two loops

How does it work ?

The Clapping music consists in one pattern being played and shifted by two people. We will use two speakers to differentiate the two musical lines and to produce a stereo effect. The Arduino board will dispatch the tone information to the speakers thanks to two nested for loops and two if conditions.

Technologies involved

The Arduino program is very close to C.

Steps

1. We are defining the pattern
2. Each speaker will act as a different channel
3. The pattern is being repeated and shifted
4. Because the tone function in Arduino cannot play several notes simultaneously, we are tricking human sound perception : two sounds played one after the other very quickly (10 milliseconds in this example) will be interpreted by our brain as simultaneous.

Source code

// This is telling the board which pin to use as an output
int speakerHigh = 8;
int speakerLow = 7;

// This will be the frequency of the notes
int noteValue = 3000;

// This will be the duration of the notes and the pause between them
int theDelay = 10;

// This is the pattern 
char pat[] = "xxx xx x xx ";

// This is the pattern lenght
int patlen = strlen(pat);
 
void setup(){} 
  void loop (){
    
    // This tells the program to begin a new measure after twelve notes have been played 
    for (int iLine=0; iLine<patlen; iLine++){
    
      // The following loop will be completed first, then launched again by the previous one.
      for (int iNote1=0; iNote1<patlen; iNote1++){
      
          // iNote2, which represents the notes of the second channel, will be assigned a number value resulting from the addition of the two nested loops
          int iNote2 = iNote1+iLine;
          
            // When the number value of iNote2 is bigger than 11, it's been resetted to 0, so that all the number values will correspond to a position in the pattern  
            if (iNote2 > (patlen-1)){
              iNote2 = iNote1-patlen+iLine;
            }
  
          // Channel one 
          // The if condition will match each note number value with a position in the pattern, checking if it refers to an "x" or a blank space
          if (pat[iNote1] == 'x') {
            // We have to shut the other speaker in order to make this one play
            noTone(speakerHigh);
            // The note is finally played
            tone(speakerLow, noteValue, theDelay);
            delay(theDelay);
          }
          // Channel two
          // The second channel is played 10 milliseconds after the first, simulating a simultaneous playing.
          if (pat[iNote2] == 'x') {
            noTone(speakerLow);
            tone(speakerHigh, noteValue, theDelay);
          }
   
      delay(theDelay*theDelay);    
    }  
  }
}

Version II : C code and the modulo

How does it work ?

Because the previous code is not as efficient as it can get, we will see how it can be optimised in C. Instead of sending it to the Arduino board, we will create a visual output in the linux shell. The result will show a list of X and blank spaces.

Technologies involved

C.

Steps

1. This time we are really using nested loops but without any if.
2. Changing the pattern is made possible by assigning to a variable a value that depends on two integer in two different loops. Whereas one of the integer will change every cycle in the smaller loop, the bigger loop that contains the other integer will change its value only when the smaller loop is over.
3. One key point of this code is the modulo.

What is the modulo ?

The modulo (a.k.a. %), will give the remainder of a division.

Example :
5%4 = 1 (divide 5 per 4 and 1 will remain)
5%3 = 2 (divide 5 per 4 and 2 will remain)
5%6 = no effect (divide 5 per 6 and you have no remainder)

It is useful to get rid of too many if conditions. By using i%12, the output will never be more than 12. If i goes higher than twelve, the result of i%12 will be the reminder, i.e. it will go from 1 to 12 again.

Source code

#include "stdio.h"
#include "string.h"

char pat[] = "xxx xx x xx ";
int patlen;
// When iShift is going up, the second channel pattern is changed
int iShift = 0;
// iRepeat make each measure repeating twelve times
int iRepeat = 0;
// iNote creates the pattern in the first channel
int iNote = 0;
// iNote2 creates the pattern in the second channel
int iNote2 = 0;

int main(){
  patlen = strlen(pat);

  // This will shift the pattern and create a new measure
  while (iShift <= patlen) {	 

    // This will repeat each mesure twelve times
    while (iRepeat < patlen) { 

      // This will play each measure twelve times
      while ( iNote < patlen) {

        // Because iShift increase at each new measure, the pattern will be shifted accordingly 
        iNote2 = iNote+iShift;
        // We print the first channel, and the second channel
        printf("%c%c\n", pat[iNote], pat[iNote2%12]);
        iNote++;
      }
      iRepeat++;
      iNote=0;
    }
    iShift++;
    iRepeat = 0;
  }
}