Revision 0:7ae9ba701ec5, committed 2015-04-15

Comitter:

tgartlan

Date:

Wed Apr 15 14:08:29 2015 +0000

Commit message:

This is a simple experiment to try and ascertain the maximum reconstruction frequency of the DAC. A sine wave is created with 512 samples. We observe the real frequency of the sine wave on the scope. The reconstruction frequency is 512*frequency.

Changed in this revision

diff -r 000000000000 -r 7ae9ba701ec5 main.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Wed Apr 15 14:08:29 2015 +0000
@@ -0,0 +1,44 @@
+#include "mbed.h"
+
+DigitalOut myled(LED1);
+AnalogOut Aout(p18);
+
+//Note if w_hat is pi/4 this means 8 samples/period. If we measure frequency of this output signal.
+//then reconstruction frequency is 8 times this.
+//Could put it through a low pass filter to smooth out.
+//Also check the offset.
+
+//Sine wave reconstruction in this case is much faster(tahn test4_sine) since I calculate the sample values before hand.
+//Sine wave period is 2.2*5us = 12us
+//Sine wave freq = 83KHz
+//Reconstruction freq is 666KHz
+
+
+
+unsigned short n;
+#define pi 3.1415192
+#define N 64                  //Numebr of samples in one period 
+#define w_hat 2*pi/N          //Normalised radian frequency               
+float sine1 [N];              //contains sine wave sample values
+
+void init_sine_array(void);
+
+int main() {
+    init_sine_array();
+    n=0;
+    while(1) {
+        
+            Aout = sine1[n];
+            n=(n+1)%N;
+    }
+}
+
+void init_sine_array(void)
+{
+    unsigned short n = 0;
+    for (n=0;n<N;n++)
+    {
+        sine1[n] = 0.5 + 0.5*sin(n*w_hat);   //note the 0.5 V of offset since DAC outputs voltage between 0 and 3.3V
+    }
+    
+ }   

diff -r 000000000000 -r 7ae9ba701ec5 mbed.bld
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed.bld	Wed Apr 15 14:08:29 2015 +0000
@@ -0,0 +1,1 @@
+http://mbed.org/users/mbed_official/code/mbed/builds/8a40adfe8776
\ No newline at end of file