Thomas Gartlan / Mbed 2 deprecated DSP1_Sine_wave_2

Sysnthesizin a sine wave at an exact frequency since the reconstruction frequency is fixed.

Dependencies:   mbed

main.cpp@0:508f6e503222, 2017-03-07 (annotated)

Committer:
tgartlan
Date:
Tue Mar 07 12:20:07 2017 +0000
Revision:
0:508f6e503222
Sinewave reconstructed from memory with a precise frequency

Who changed what in which revision?

UserRevisionLine numberNew contents of line
tgartlan 0:508f6e503222 1 #include "mbed.h"
tgartlan 0:508f6e503222 2
tgartlan 0:508f6e503222 3 DigitalOut myled(LED1);
tgartlan 0:508f6e503222 4 AnalogOut Aout(p18);
tgartlan 0:508f6e503222 5 Ticker tick1;
tgartlan 0:508f6e503222 6 //Note in this case could reconstruct at known frequency using timer(ticker)
tgartlan 0:508f6e503222 7 //125 us ticker gives us 8KHz reconstruction
tgartlan 0:508f6e503222 8 //8 samples/period means frequency should be 1KHz
tgartlan 0:508f6e503222 9 //works perfectly
tgartlan 0:508f6e503222 10
tgartlan 0:508f6e503222 11
tgartlan 0:508f6e503222 12
tgartlan 0:508f6e503222 13
tgartlan 0:508f6e503222 14 unsigned short n=0;
tgartlan 0:508f6e503222 15 #define pi 3.1415192
tgartlan 0:508f6e503222 16 #define N 8 //Numebr of samples in one period
tgartlan 0:508f6e503222 17 #define w_hat 2*pi/N //Normalised radian frequency
tgartlan 0:508f6e503222 18 float sine1 [N]; //contains sine wave sample values
tgartlan 0:508f6e503222 19
tgartlan 0:508f6e503222 20 void output_sample(void);
tgartlan 0:508f6e503222 21 void init_sine_array(void);
tgartlan 0:508f6e503222 22
tgartlan 0:508f6e503222 23 int main() {
tgartlan 0:508f6e503222 24 init_sine_array();
tgartlan 0:508f6e503222 25 tick1.attach_us(&output_sample,3); //125 us is 8Khz //limit is 3us which means ~333KHz max fs
tgartlan 0:508f6e503222 26 while(1) {
tgartlan 0:508f6e503222 27 }
tgartlan 0:508f6e503222 28 }
tgartlan 0:508f6e503222 29
tgartlan 0:508f6e503222 30 void output_sample(void)
tgartlan 0:508f6e503222 31 {
tgartlan 0:508f6e503222 32 Aout = sine1[n];
tgartlan 0:508f6e503222 33 n=(n+1)%N;
tgartlan 0:508f6e503222 34 }
tgartlan 0:508f6e503222 35
tgartlan 0:508f6e503222 36 void init_sine_array(void)
tgartlan 0:508f6e503222 37 {
tgartlan 0:508f6e503222 38 unsigned short n = 0;
tgartlan 0:508f6e503222 39 for (n=0;n<N;n++)
tgartlan 0:508f6e503222 40 {
tgartlan 0:508f6e503222 41 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
tgartlan 0:508f6e503222 42 }
tgartlan 0:508f6e503222 43
tgartlan 0:508f6e503222 44 }