File content as of revision 0:88f7ab41bdce:

#include "mbed.h"

DigitalOut myled(LED1);

DigitalIn pushButton(p23);
DigitalIn rotaryA(p21);
DigitalIn rotaryB(p22);

AnalogIn pressure(p20);
AnalogIn pos1(p17);
AnalogIn top(p16);
AnalogIn bottom(p15);

float wiper_f;
float top_f;
float bottom_f;
float vol_f;
float tmp_f;
int tmp_i;

float pressureAvg[4];
float wiperAvg[4];

AnalogOut signal(p18);

Ticker sampleClock;
// 16 entry sinewave table.
char sineWave[]={127,175,216,244,255,244,216,175,127,78,37,9,0,9,36,78};

char sawWave[]={0,16,31,47,64,79,95,111,127,143,159,175,191,207,223,255};

unsigned int counter;
unsigned  int counterSum;
unsigned int counterLimit = 2147483647; //31 bits  2^31 - 1

char temp;

float byteToFloat(char in){
    float i = in;
    return (i/255.0)*0.5;
}

void sample2(){
    


}

void sample(){
 
    //useing a 31 bit counter.
    counter = counter + counterSum;
    if(counter > counterLimit){
        //wrap the counting.
        counter = counter - counterLimit;
    }
    
    //Fout = CounterSum*Fclk/MaxCount
    
    temp = counter>>27;  //shift the top 4 bits down.
    //float x = temp;
    //signal.write(x/16.0);
    
    //write the output out 
    signal.write(vol_f*byteToFloat(sineWave[temp]) +0.5);    
}

int read_encoder()
{
  int8_t enc_states[] = {0,-1,1,0,1,0,0,-1,-1,0,0,1,0,1,-1,0};
  static char old_AB = 0;
  /**/
  old_AB <<= 2;
  char x  = rotaryA.read();
  x<<=1;
  x = x+rotaryB.read();                 //remember previous state
  old_AB |= ( x & 0x03 );  //add current state
  return ( enc_states[( old_AB & 0x0f )]);
}

int main() {
    
    //setup variables.
    tmp_i = 0;
    counter = 0;
    counterSum = 302365697;
    counterSum = 18897856;
    //counterSum = 1181116;
    //18897856.1
    
    vol_f = 0.0;
    
    //hook up sample() to the ticker.  run the counter at 50kHz
    sampleClock.attach_us(sample,20);
    
    while(1){
        wiper_f = pos1.read();
        bottom_f = bottom.read();
        
        if(wiper_f >= bottom_f){
            // wiper is being pressed, play a note
            top_f = top.read();
            
            tmp_f = 1.0 - (wiper_f - bottom_f)/(top_f - bottom_f);
            
            vol_f = 1.0 - pressure.read();
            //ribbon is about 3 octaves worth.
            //if the top is 440Hz = 18897856.1
            //44Hz = 1889785.61
            //55Hz is 2362232.013 //low A
            tmp_i = (int)(16535624*tmp_f);
            
            counterSum = 2362232+ tmp_i;
            
        }else{
            vol_f = 0.0;
        }
    
    
    }
}