Thomas Gartlan
Sysnthesizin a sine wave at an exact frequency since the reconstruction frequency is fixed.
Revision 0:508f6e503222, committed 2017-03-07
- Comitter:
- tgartlan
- Date:
- Tue Mar 07 12:20:07 2017 +0000
- Commit message:
- Sinewave reconstructed from memory with a precise frequency
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 |
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp Tue Mar 07 12:20:07 2017 +0000
@@ -0,0 +1,44 @@
+#include "mbed.h"
+
+DigitalOut myled(LED1);
+AnalogOut Aout(p18);
+Ticker tick1;
+//Note in this case could reconstruct at known frequency using timer(ticker)
+//125 us ticker gives us 8KHz reconstruction
+//8 samples/period means frequency should be 1KHz
+//works perfectly
+
+
+
+
+unsigned short n=0;
+#define pi 3.1415192
+#define N 8 //Numebr of samples in one period
+#define w_hat 2*pi/N //Normalised radian frequency
+float sine1 [N]; //contains sine wave sample values
+
+void output_sample(void);
+void init_sine_array(void);
+
+int main() {
+ init_sine_array();
+ tick1.attach_us(&output_sample,3); //125 us is 8Khz //limit is 3us which means ~333KHz max fs
+ while(1) {
+ }
+}
+
+void output_sample(void)
+{
+ 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
+ }
+
+ }
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/mbed.bld Tue Mar 07 12:20:07 2017 +0000 @@ -0,0 +1,1 @@ +http://mbed.org/users/mbed_official/code/mbed/builds/8a40adfe8776 \ No newline at end of file