main.cpp

00001 #include "mbed.h"
00002 
00003 //Number of dutycycle steps for output wave
00004 #define SINE_STEPS        32
00005 //Frequency of output sine in Hz
00006 #define SINE_OUT_FREQ     1000
00007 
00008 //Constants to compute the sine waveform
00009 #define PI                 3.141592f
00010 #define SINE_STEPS_RAD    (2.0f * PI / (float)SINE_STEPS)
00011 
00012 //Table to generate the sine waveform using dutycycles
00013 float sine_duty[SINE_STEPS];
00014 
00015 
00016 //Frequency of Pulse Width Modulated signal in Hz
00017 #define PWM_FREQ          200000
00018 
00019 //PWM pin
00020 PwmOut PwmPin (p22);
00021 
00022 //Heartbeat LED
00023 DigitalOut myled(LED1);
00024 
00025 
00026 //Ticker to update the PWM dutycycle
00027 Ticker pwm_ticker;
00028 
00029 //Ticker calls this fucntion to update the PWM dutycycle
00030 void pwm_duty_updater() {
00031   static int idx=0;
00032   
00033   PwmPin.write(sine_duty[idx]);  // Set the dutycycle % to next value in array
00034   idx++;                         // Increment the idx
00035   if (idx == SINE_STEPS) idx=0;  // Reset the idx when teh end has been reached  
00036 
00037 }
00038   
00039 int main() {
00040   int i;
00041   
00042   // Init the duty cycle array
00043   for (i=0; i<SINE_STEPS; i++) {
00044     sine_duty[i] = ( sin(i * SINE_STEPS_RAD) + 1.0f ) / 2.0f;  // convert sine (-1.0 .. +1.0) into dutycycle (0.0 .. 1.0)
00045   }  
00046     
00047   // Set PWM frequency to 200 KHz (period = 5 us)
00048   PwmPin.period( 1.0f / (float) PWM_FREQ);
00049 
00050   // Init the Ticker to call the dutycyle updater at the required interval
00051   // The update should be at (SINE_STEPS * SINE_OUT_FREQ) 
00052   pwm_ticker.attach(&pwm_duty_updater, 1.0f / (float)(SINE_STEPS * SINE_OUT_FREQ));
00053 
00054   while(1){ //infinite loop
00055     myled = !myled; 
00056     wait(0.5);  
00057   }
00058        
00059 } 
00060