Wayne McLachlan / Mbed 2 deprecated sine3-v2

Uses trigonometry to produce high quality 3 phase sinewave output waveworms on the PWM. Tested from 30 to 100Hz at 10kHz modulation. Changes frequency glitch free. Amplitude is scalable. Could be used as a basic invertor back-end. Not optimised for processor overhead, could be modified to use lookup tables if less accuracy required. Oscilloscope trace here: http://mbed.org/users/waynemcl/notebook/sine3-v2/

Dependencies:   mbed

main.cpp

Committer:
waynemcl
Date:
2010-11-28
Revision:
0:d040778370fc

File content as of revision 0:d040778370fc:

#include "mbed.h"
#include "stdio.h"

#define PI 3.1416

// License: You may copy or modify and re-use this code, but you MUST credit me:
// Wayne McLachlan, www.embeddedengineering.co.nz
// You may add your name to the author list if you have done significant modifications or improvements

PwmOut chA(p21);
PwmOut chB(p22);
PwmOut chC(p23);

Serial pc(USBTX, USBRX);
Ticker sine3ticker;

#define SINE3_PWM_FREQ 10000

unsigned char   sine3freq;
float           sine3mag;
float           sine3theta;

void sine3tick() {
        // offset PWM for bipolar: 0.5 => 0V
        chA = 0.5 + (sine3mag * sinf(sine3theta) /2);
        chB = 0.5 + (sine3mag * sinf(sine3theta + 2*PI  /3)/2);   // + 120 degrees
        chC = 0.5 + (sine3mag * sinf(sine3theta + 2*PI*2/3)/2);   // + 240 degrees => - 120 degrees
                
        sine3theta +=  2*PI / (SINE3_PWM_FREQ / sine3freq); // one cycle / steps per cycle
        if (sine3theta >=  2*PI) {
            sine3theta = 0;
        }
}


void sine3_init() {
    chA.period_us( 1000000 / SINE3_PWM_FREQ );   // period in uS. Common to all PWM
    chA = 0.5;
    chB = 0.5;
    chC = 0.5;
    
    sine3mag = 0.9;                             // prevent overmodulation
    sine3freq = 55;                             // compromise between 50Hz and 60Hz
    sine3theta = 0;
    sine3ticker.attach_us(&sine3tick, (1000000 / SINE3_PWM_FREQ) ); // period in uS
    //pc.printf("\n\r init ");
}


int main() {
    sine3_init();
    while (1) {
        sine3freq++;
        if (sine3freq > 100) {
            sine3freq = 30;
            pc.printf("\n\r");
        }
        wait(0.2);
        pc.printf("%d ",sine3freq);
    }
}