FRDM-K64F Code Share
A test for a digital envelope detector using a rectifier and a low-pass filter. The program first creates sample vectors for sinusoidal waves of 2Hz and 20Hz (considering 1kHz sampling frequency). Then, every 10ms it generates a new sample for a modulated wave (multiply both waves), and passes it through a full-wave rectifier and a Chebyshev low-pass filter with cutoff frequency of 5Hz. Then it sends the original wave and the recovered envelope through serial port in CSV format. I used 10ms interval instead of 1ms because otherwise the serial speed would have to be too high.
Dependencies: mbed
Revision 0:1ba9469c839f, committed 2014-08-26
- Comitter:
- quevedo
- Date:
- Tue Aug 26 17:02:29 2014 +0000
- Commit message:
- Original program;
Changed in this revision
| main.cpp | Show annotated file Show diff for this revision Revisions of this file |
| mbed.bld | Show annotated file Show diff for this revision Revisions of this file |
diff -r 000000000000 -r 1ba9469c839f main.cpp
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp Tue Aug 26 17:02:29 2014 +0000
@@ -0,0 +1,76 @@
+#include "mbed.h"
+#include "math.h"
+#define PI 3.1415926536
+//#define GAIN 2.661812926e+05 // For Buttherworth
+#define GAIN 3.676489487e+05 // For Chebyshev
+
+// Pin and timer setup
+DigitalIn b0(PTA4);
+Serial pc(USBTX, USBRX);
+Ticker samp;
+
+double in, rect, out;
+double xv[4], yv[4];
+double s2[500], s20[50];
+int i, i2, i20;
+
+// ISR for periodical interrupt
+void newsample(void) {
+ in = s2[i2] * s20[i20];
+ i2++;
+ if(i2 > 499) {
+ i2 = 0;
+ }
+ i20++;
+ if(i20 > 49) i20 = 0;
+ i++;
+
+ rect = abs(in); // Full-wave rectification
+ // The filter is low-pass IIR 3rd-order -0.5dB Chebyshev, cutoff frequency 5Hz for 1kHz samples.
+ // Design was made through the website: http://www-users.cs.york.ac.uk/~fisher/mkfilter/
+ xv[0] = xv[1];
+ xv[1] = xv[2];
+ xv[2] = xv[3];
+ xv[3] = rect / GAIN;
+ yv[0] = yv[1];
+ yv[1] = yv[2];
+ yv[2] = yv[3];
+ //yv[3] = xv[0] + xv[3] + 3 * (xv[1] + xv[2]) + (0.9390989403 * yv[0]) + (-2.8762997235 * yv[1]) + (2.9371707284 * yv[2]); // For Butterworth
+ yv[3] = xv[0] + xv[3] + 3 * (xv[1] + xv[2]) + (0.9614041736 * yv[0]) + (-2.9213338983 * yv[1]) + (2.9599079648 * yv[2]); // For Chebyshev
+ out = yv[3];
+
+ printf("%f,%f\r\n", in, out);
+}
+
+void initfilter(void) {
+ char k;
+ for(k = 0; k < 4; k++) {
+ xv[k] = 0;
+ yv[k] = 0;
+ }
+}
+
+// Main function
+int main() {
+ initfilter();
+ pc.baud(57600);
+
+ for(i = 0; i < 50; i++) {
+ s20[i] = sin(i*PI/25);
+ }
+ for(i = 0; i < 500; i++) {
+ s2[i] = sin(i*PI/250);;
+ }
+ i2 = 0;
+ i20 = 0;
+ i = 0;
+ while(b0); // waits for PB0 push
+ samp.attach(&newsample, 0.01); // periodical interrupt every 10ms
+ while(i < 5000) {
+ //
+ }
+ samp.detach();
+
+ while(1) {
+ }
+}
diff -r 000000000000 -r 1ba9469c839f mbed.bld --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/mbed.bld Tue Aug 26 17:02:29 2014 +0000 @@ -0,0 +1,1 @@ +http://mbed.org/users/mbed_official/code/mbed/builds/9327015d4013 \ No newline at end of file