--> 8051 single-chip pulse width modulation (PWM) brightness control of LED lights

This program is used to control an LED brightness through PWM. Since the AT89S52 dont have a hardware PWM we are using an software PWM with help of the timer 0.
By changing the duty cycle of the PWM signal we can control the brightness of the LED. The brightness is varied from 0-10
Here's the circuit diagram and the C code

[code:c]/*Program of 8051 single-chip pulse width modulation (PWM) brightness control of LED lights, as we all know 8051 does not have an pwm interface on it. This process is simulated by software PWM. The adjustment of high and low duty cycle of the square wave frequency can be realized to control LED brightness*/
#include "AT89X51.H" //simulation of PWM output control lamp brightness level of 10 
unsigned int scale; //duty cycle control variable 
void main(void) // main program 
{ unsigned int n; //delay cycle variables  
TMOD=0x02; //timer 0, mode 2 (0000,0010), 8-bit timer mode 
TH0=0x06; //write the timer 0 preset initial value, so that an overflow of 250 microseconds (12MHz) 
TL0=0x06; //written into the preset value  
TR0=1; //start timer  
ET0=1; //allow timer 0 interrupt  
EA=1; //Enable global interrupt 
while(1) //infinite loop, the main work is done here
{ for(n=0;n<50000;n++); //every time, automatically increases the brightness of a grade 
scale++; //duty cycle control variable scale plus 1  
if(scale==10) scale=0; //if the scale = 10, so that scale is 0  
} } 
timer0() interrupt 1 //Timer 0 interrupt service routine 
{ static unsigned int tt ; //tt used to save the current time in a second location in the proportion of 
tt++; //microsecond increase of 1 per 250 
if(tt==10) //2.5 ms cycle clock  
{ tt=0; //so that tt = 0, start a new cycle of the PWM 
P3_0=0; //make LED lights ON 
} 
if(scale==tt) //in accordance with the present duty cycle output for high switching 
P3_0=1; //make LED lights OFF  
} 
/*Process tt = 0 from the beginning to the low scale from the scale to the tt = 10 for high,