main.cpp

00001 #include "mbed.h"
00002 
00003 
00004 DigitalOut myled(LED1);
00005 DigitalOut led(LED2);
00006 DigitalOut led2(LED3);
00007 DigitalOut led3(LED4);
00008 const int N=1024;  // Sample number
00009 struct TWIDDLE {  // Structure factor for calculate fft
00010 
00011     float cosval [N/2];
00012     float sinval [N/2];
00013 
00014 };
00015 void FFT(float datos[N], int n, TWIDDLE &w); //Declaration of functions
00016 void enviodatos(float datos[N], int n);
00017 Serial pc(USBTX, USBRX);  //Declaration Serial port
00018 
00019 int main() {        //Main program
00020     myled.write(0);
00021     led.write(0);
00022     led2.write(0);
00023     led3.write(0);
00024     int i;        //Parameters to calculate the values of a sine function. DATOS[N]=Amp*sin(w0*t)
00025     float arg;
00026     arg=2*3.1416/N; //argument of the structure TWIDDLE
00027     float tm,t,w0,T, Amp;
00028     tm=0.1; // increments of time (0,1seg)
00029     t=0; //initial time
00030     T=2*3.1416; //Period of signal
00031     w0=(2*3.1416/T); // angular frequency
00032     Amp=3;  //Amplitude
00033     struct TWIDDLE W; //Declarate of a type structure
00034 
00035     for (i=0; i<N/2; i++) { //Calculate all the TWIDDLE factors
00036         W.cosval[i]= cos(i*arg);
00037         W.sinval[i]= -sin(i*arg);
00038     }
00039 
00040     float DATOS[N]; //array to save the sinus values
00041     for (i=0; i<N; i++) { //calculate the sinus values
00042         DATOS[i]=Amp*sin(w0*t);
00043         t+=tm;
00044     }
00045     led.write(1); //Execution of the program to here OK
00046     FFT(DATOS,N,W); //Function to calculate FFT
00047     enviodatos(DATOS,N); //Function to send values to serial port
00048     led3.write(1); //Execution of the program to here OK
00049     while (1); //
00050 
00051 }
00052 
00053 void FFT(float datos[N], int n,TWIDDLE &w) {
00054     float temp1, temp2, temp3,temp4;   //variables needed to calculate FFT
00055     int i,j,k,p;
00056     int upper_leg, lower_leg;
00057     int leg_diff;
00058     int num_stages=0;
00059     int index, step;
00060     float datos_real[n], datos_imag[n]; //real and imaginary values
00061     for (p=0; p<n; p++) {
00062         datos_real[p]=datos[p];
00063         datos_imag[p]=0;
00064     }
00065     led2.write(1); // Execution of the program to here break it if N=>2048, else OK.
00066     i=1;
00067     do {
00068         num_stages+=1;
00069         i=i*2;
00070     } while (i!=n);
00071 
00072     leg_diff=n/2;
00073     step=1;
00074 
00075     for (i=0; i<num_stages; i++) {
00076         index=0;
00077         for (j=0; j<leg_diff; j++) {
00078             for (upper_leg=j; upper_leg<n; upper_leg+=(2*leg_diff)) {
00079                 lower_leg=upper_leg+leg_diff;
00080 
00081                 temp1= (datos_real[upper_leg]+ datos_real[lower_leg]);
00082                 temp2= (datos_real[upper_leg]- datos_real[lower_leg]);
00083                 temp3= (datos_imag[upper_leg]+ datos_imag[lower_leg]);
00084                 temp4= (datos_imag[upper_leg]- datos_imag[lower_leg]);
00085                 datos_real[lower_leg]= (temp2*w.cosval[index])-(temp4*w.sinval[index]);
00086                 datos_imag[lower_leg]= (temp2*w.sinval[index]+temp4*w.cosval[index]);
00087                 datos_real[upper_leg]= temp1;
00088                 datos_imag[upper_leg]= temp3;
00089             }
00090             index+=step;
00091         }
00092         leg_diff=leg_diff/2;
00093         step*=2;
00094     }
00095 //bit reversal
00096 
00097     j=0;
00098     for (i=1; i<(N-2); i++) {
00099         k=n/2;
00100         while (k<=j) {
00101             j=j-k;
00102             k=k/2;
00103         }
00104         j=j+k;
00105 
00106         if (i<j) {
00107             temp1= datos_real[j];
00108             temp2= datos_imag[j];
00109             datos_real[j]=datos_real[i];
00110             datos_imag[j]=datos_imag[i];
00111             datos_real[i]=temp1;
00112             datos_imag[i]=temp2;
00113         }
00114     }
00115 
00116     for (i=0; i<n; i++) {
00117 
00118         datos[i]= pow(sqrt(pow(datos_real[i],2)+pow(datos_imag[i],2)),2); //Calculate the power fft
00119     };
00120 
00121 }
00122 
00123 void enviodatos(float datos[N],int n) {
00124     int i=0,j=0,k=0,aux=0; //send to serial port the values correctly.
00125     unsigned char bytes[4];
00126     float dato;
00127 
00128     for (i=0; i<n; i++) {
00129         dato=datos[i];
00130         aux=dato;
00131         for (j=0; j<4; j++) {
00132             switch (j) {
00133                 case 0:
00134                     bytes[j]=aux;
00135                     aux=aux>>8;
00136                     break;
00137                 case 1:
00138                     bytes[j]=aux;
00139                     aux=aux>>8;
00140                     break;
00141                 case 2:
00142                     bytes[j]=aux;
00143                     aux=aux>>8;
00144                     break;
00145                 case 3:
00146                     bytes[j]=aux;
00147                     aux=aux>>8;
00148                     break;
00149             }
00150         }
00151         for (k=3; k>=0; k--) {
00152 
00153             while (pc.writeable()==0);
00154             pc.putc(bytes[k]);
00155 
00156         }
00157     }
00158 }