Diff: FFT_Sampling.cpp

Revision:

0:c740f515e0b7

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/FFT_Sampling.cpp	Tue Jul 15 10:14:37 2014 +0000
@@ -0,0 +1,83 @@
+//--------------------------------------------------------------
+// Sampling and Spectrum analysis using FFT
+// Copyright (c) 2014 MIKAMI, Naoki,  2014/06/29 
+//--------------------------------------------------------------
+
+#include "mbed.h"
+#include "AdcInternal.hpp"
+#include "fftReal.hpp"
+
+using namespace Mikami;
+
+// sampling frequency
+const float FS_ = 10.0e3f;
+const int N_FFT_ = 256;
+
+Adc adc_(A0);
+Ticker timer_;      // for timer interrupt
+DigitalIn userButton_(USER_BUTTON);
+FftReal fft_(N_FFT_);
+
+float xn_[N_FFT_+1];
+volatile int count_;
+
+// Sampling
+void TimerIsr()
+{
+    xn_[count_] = adc_.Read();  // AD
+    count_++;
+}
+
+int main()
+{
+    printf("Ready.\r\n");
+    while(userButton_);     // wait for user button pressed
+    printf("User button is pushed!\r\n");
+
+    count_ = 0;
+    timer_.attach_us(&TimerIsr, 1.0e6f/FS_);
+    while (count_ < N_FFT_+1);
+    timer_.detach();        // Detach TimerIsr
+    printf("End of Sampling.\r\n");
+
+    float xnW[N_FFT_];      // for windowed data
+    Complex yk[N_FFT_/2+1];
+    float yDb[N_FFT_/2+1];
+    
+    // Windowing
+    float pi2N = 6.283185f/N_FFT_;
+    for (int n=0; n<N_FFT_; n++)
+        xnW[n] = (xn_[n+1] - xn_[n])*(0.54f - 0.46f*cosf(pi2N*n));
+        
+    // Execute FFT
+    fft_.Execute(xnW, yk);
+    
+    // Square of absolute value of FFT
+    for (int n=0; n<=N_FFT_/2; n++)
+        yDb[n] = norm(yk[n]);
+        
+    // Get maximum value of yk[n]
+    float max = 0;
+    for (int n=0; n<=N_FFT_/2; n++)
+        max = (yDb[n] > max) ? yDb[n] : max;
+        
+    // Normalized spectra to dB
+    for (int n=0; n<=N_FFT_/2; n++)
+        if (yDb[n] > 0)
+            yDb[n] = 10.0f*log10f(yDb[n]/max);
+        else
+            yDb[n] = -100.0f;
+
+    // Output to terminal
+    float dt = 1.0e3f/FS_;
+    float df = FS_/N_FFT_;
+    for (int n=0; n<N_FFT_; n++)
+    {
+        if (n <= N_FFT_/2)
+            printf("%3d, %4.1f,%8.4f, %10.4f,%6.1f\r\n",
+                   n, n*dt, xn_[n], n*df, yDb[n]);
+        else
+            printf("%3d, %4.1f,%8.4f\r\n", n, n*dt, xn_[n]);
+    }
+}
+