Dear All,
I am trying to do the fft using F28335 where i am using current sensor to have signals to do the fft. The current sensors are working fine and giving sinosoidal current. I think that the FFT part in the code is ok. But,the fft in the graph window is not showing exactly i want. Some one suggested me to check the ADC sampling frequency. I did so. I made to 250 Hz using the method described in controlsuite (put AdcRegs.ADCTRL3.bit.ADCCLKPS = 0x8F0D1;). As the system frequency is 15MHz i had to do so. I am still confused how to do that initialization of the ADC sampling and all this staffs. The code i am using is given below. The FFt plot i got in the graph window is also attached here.2480.FFT found.docx
Please anyone help me to get proper FFT using that one.
// Global variables used in this system
#ifndef M_PI
#define M_PI 3.14159265358979324
#endif
int nn;
int aa;
#define N 128
void compute_dft(double inreal[N], double inimag[N], double outreal[N], double outimag[N], int n);
double inputsignal[N] = {0};
double inputimag[N] = {0};
double inreal[N]={0};
double inimag[N]={0};
double outreal[N]={0};
double outimag[N]={0};
double result1[N/2]={0};
double THD;
float num=0;
float F=0;
void main(void){
DeviceInit();
// Initialize ADC
ChSel[0]=0;
ChSel[1]=2;
ChSel[2]=4;
ChSel[3]=6;
ChSel[4]=8;
// Initialize ADC module
ADC_MACRO_INIT(ChSel,TrigSel,ACQPS)
#ifdef DSP2833x_DEVICE_H
clarke1.As=((AdcMirror.ADCRESULT0)*0.00024414-offsetA)*2*0.909; // Phase A curr.
clarke1.Bs=((AdcMirror.ADCRESULT1)*0.00024414-offsetB)*2*0.909; // Phase B curr.
#endif
if (nn < N)
{ nn++;
inputsignal[nn]= (double)clarke1.As;
inputimag[nn] = 0;
}
else
{
compute_dft(inputsignal, inputimag, outreal, outimag, N);
nn=0;
}
}
void compute_dft(double inreal[N], double inimag[N], double outreal[N], double outimag[N], int n)
{
int k, m;
for (k = 0; k < n; k++) { /* For each output element */
double sumreal = 0;
double sumimag = 0;
int t;
//n=250;
for (t = 0; t < n; t++) { /* For each input element */
double angle = 2 * M_PI * t * k / n;
sumreal += inreal[t] * cos(angle) + inimag[t] * sin(angle);
sumimag += -inreal[t] * sin(angle) + inimag[t] * cos(angle);
}
outreal[k] = sumreal;
outimag[k] = sumimag;
}
for (m=0; m < N/2-1; m++)
{
result1[m]=sqrt(outreal[m]*outreal[m]+outimag[m]*outimag[m]);
}
BR
Arafat
