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Friday, 22 June 2012

PWM generation of microcontroller 8051 for SCR or triac power control

The code of program for PWM with microcontroller 8051 for SCR or triac power control is written c lanuage using keil compiler. The c-code for PWM is as follows.
/* This project is develop to generate two seperate channel PWM signals at 50HZ frequency
The duty cycle of the pulses is variable subject to the input on Port1 and port2.
The output PWM signal can be used to drive SCR or triacs to control the phase angle and power of any load with suitable hardware interface.
Please not that in this project the OPAMP are used to convert the pulses to 0 - 5 V, means you can use it in as two channel DAC also.
But for triac or SCR interface the OPAMP circuit will be re-placed with proper optocoupler like moc3020 and scrs.89c51 as pwm controller
*/

#include
unsigned char ch_count[2];// two channel counts array
unsigned char ch_duty_level[2];// level of the duty cycle
bit int_10ms;// this is a flag wich is set every 10msec time period
sbit PWM1 = P3^6;
sbit PWM2 = P3^7;
sbit indicator = P3^5;
void external_interrupt (void) interrupt 0
// external interrupt for zero crossing dectection
{
ch_count[0]=ch_duty_level[0];
// on zero crossing detection, counts are updated for both PWM channels
ch_count[1]=ch_duty_level[1];
PWM1=0; // the output is active low
PWM2 =0;//89c51 as pwm controller
int_10ms = 1; // 10msec flag is set
}
void timer_interrupt (void) interrupt 1
// The timer 0 is used for the duty cycle adjustement of two channel PWM
{
TL0 = 0XE2; //reset timer LSB

if(--ch_count[0]==0) PWM1 = 1;
// each time the timer interrupt occur the counts are decreased by one and on reaching zero
if(--ch_count[1]==0) PWM2 = 1;
// the outputs are turned off, as the out put is active low

}
void main (void)
{

ET0 = 1; // enables the Timer 0 interrupt of 8051
TMOD = 0x02;
// timer mode register, timer 0 is used in mode 2
TL0 = 0XE2; // Initialize timer0 LSB
TR0 = 1; // timer 0 is activated
EX0 = 1; // external inturpt is activated
IT0 = 1;
EA = 1;
ch_duty_level[0] = 30; // dummy value for duty cycle for PWM 1
ch_duty_level[1] = 60; // dummy value for duty cycle for PWM 2
while (1) // endless loop
{
if( int_10ms){
int_10ms = 0;
ch_duty_level[0] = P1;
// take the input value of duty cycle for PWM 1 fromport1 of the 8051
ch_duty_level[1] = P2;
// take the input value of duty cycle for PWM 2 fromport1 of the 8051
indicator =~ indicator;
}
}
}

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