Justin's Tech

A different take on how to create a PWM signal. I decided to go the interrupt route using the WDT+ peripheral. I did this by setting it to the interval timer and putting all my counters and logic within the interrupt. The funny thing is  i have read that you shouldn’t put too much code into your interrupt, or something bad will happen.

the resistors on the left, are 100 ohm resistors and the one on the right is a 470 ohm resistor to limit current for the RGB LED. connections on the uC that are used are pins 1.3, 1.4, 1.5 i have not decided which pins are what color, i will decide that on my final build.

The test code will be improved this is just the compile and see if it works.- The best part , the code works lol .

so let me know what you think on creating PWM with the interval timer instead of timer A.

#include <msp430x20x2.h>
#include <signal.h> //add for interrupt
#define UP 0x00
#define DOWN 0x01
volatile  int millsecs = 0;
volatile  int counter2 = 0;
volatile  int led_red = 0;
volatile  int led_green = 199;
volatile  int led_blue = 199;
volatile  int dir = UP;
void main(void)
{
WDTCTL = WDT_MDLY_0_064;
P1DIR |= BIT5 + BIT4 + BIT3;
P1OUT |= BIT5 + BIT4 + BIT3;
IE1 |= WDTIE;
eint();
}//end main
interrupt(WDT_VECTOR) watchdog_timer(void)
{
++millsecs;
if (millsecs == 200) { millsecs= 0; P1OUT |= BIT0 + BIT6; ++counter2; }
if (millsecs == led_red ) { P1OUT ^= BIT3; }
if (millsecs == led_green) { P1OUT ^= BIT4; }
if (millsecs == led_blue ) { P1OUT ^= BIT5; }
if (counter2 == 25 ) { counter2 =0;
switch (dir){
case UP: ++led_red; --led_green; --led_blue;
if (led_red == 199) {dir = DOWN;}
break;
case DOWN: --led_red; ++led_green; ++led_blue;
if (led_red == 0) {dir = UP;}
break;
}//end switch
}//end if
}//end interrupt

To change the Period length – change the 200 value to the period you want, you can also change it by setting the WDT interval to different intervals to change the period.
to change the Duty cycle, change the led_[color] variable to anything between 0 and period length

I am still working on trying to get it to cycle through all colors, and fade better when led_[color] is close to 0
by far this project is not done, the board will be soldered up and pics will be presented. The end result should be code for WDT PWM, which could be used for servos, LEDs, or possibly communication, and i will have my flower pot back!