Wim Huiskamp / Mbed 2 deprecated SineFromPWM

Sine from PWM dutycycle modulation

Dependencies:   mbed

main.cpp@0:d274003b52e7, 2014-02-18 (annotated)

Committer:
wim
Date:
Tue Feb 18 20:08:15 2014 +0000
Revision:
0:d274003b52e7
PWM SINE Test;

Who changed what in which revision?

UserRevisionLine numberNew contents of line
wim 0:d274003b52e7 1 #include "mbed.h"
wim 0:d274003b52e7 2
wim 0:d274003b52e7 3 //Number of dutycycle steps for output wave
wim 0:d274003b52e7 4 #define SINE_STEPS 32
wim 0:d274003b52e7 5 //Frequency of output sine in Hz
wim 0:d274003b52e7 6 #define SINE_OUT_FREQ 1000
wim 0:d274003b52e7 7
wim 0:d274003b52e7 8 //Constants to compute the sine waveform
wim 0:d274003b52e7 9 #define PI 3.141592f
wim 0:d274003b52e7 10 #define SINE_STEPS_RAD (2.0f * PI / (float)SINE_STEPS)
wim 0:d274003b52e7 11
wim 0:d274003b52e7 12 //Table to generate the sine waveform using dutycycles
wim 0:d274003b52e7 13 float sine_duty[SINE_STEPS];
wim 0:d274003b52e7 14
wim 0:d274003b52e7 15
wim 0:d274003b52e7 16 //Frequency of Pulse Width Modulated signal in Hz
wim 0:d274003b52e7 17 #define PWM_FREQ 200000
wim 0:d274003b52e7 18
wim 0:d274003b52e7 19 //PWM pin
wim 0:d274003b52e7 20 PwmOut PwmPin (p22);
wim 0:d274003b52e7 21
wim 0:d274003b52e7 22 //Heartbeat LED
wim 0:d274003b52e7 23 DigitalOut myled(LED1);
wim 0:d274003b52e7 24
wim 0:d274003b52e7 25
wim 0:d274003b52e7 26 //Ticker to update the PWM dutycycle
wim 0:d274003b52e7 27 Ticker pwm_ticker;
wim 0:d274003b52e7 28
wim 0:d274003b52e7 29 //Ticker calls this fucntion to update the PWM dutycycle
wim 0:d274003b52e7 30 void pwm_duty_updater() {
wim 0:d274003b52e7 31 static int idx=0;
wim 0:d274003b52e7 32
wim 0:d274003b52e7 33 PwmPin.write(sine_duty[idx]); // Set the dutycycle % to next value in array
wim 0:d274003b52e7 34 idx++; // Increment the idx
wim 0:d274003b52e7 35 if (idx == SINE_STEPS) idx=0; // Reset the idx when teh end has been reached
wim 0:d274003b52e7 36
wim 0:d274003b52e7 37 }
wim 0:d274003b52e7 38
wim 0:d274003b52e7 39 int main() {
wim 0:d274003b52e7 40 int i;
wim 0:d274003b52e7 41
wim 0:d274003b52e7 42 // Init the duty cycle array
wim 0:d274003b52e7 43 for (i=0; i<SINE_STEPS; i++) {
wim 0:d274003b52e7 44 sine_duty[i] = ( sin(i * SINE_STEPS_RAD) + 1.0f ) / 2.0f; // convert sine (-1.0 .. +1.0) into dutycycle (0.0 .. 1.0)
wim 0:d274003b52e7 45 }
wim 0:d274003b52e7 46
wim 0:d274003b52e7 47 // Set PWM frequency to 200 KHz (period = 5 us)
wim 0:d274003b52e7 48 PwmPin.period( 1.0f / (float) PWM_FREQ);
wim 0:d274003b52e7 49
wim 0:d274003b52e7 50 // Init the Ticker to call the dutycyle updater at the required interval
wim 0:d274003b52e7 51 // The update should be at (SINE_STEPS * SINE_OUT_FREQ)
wim 0:d274003b52e7 52 pwm_ticker.attach(&pwm_duty_updater, 1.0f / (float)(SINE_STEPS * SINE_OUT_FREQ));
wim 0:d274003b52e7 53
wim 0:d274003b52e7 54 while(1){ //infinite loop
wim 0:d274003b52e7 55 myled = !myled;
wim 0:d274003b52e7 56 wait(0.5);
wim 0:d274003b52e7 57 }
wim 0:d274003b52e7 58
wim 0:d274003b52e7 59 }
wim 0:d274003b52e7 60