1.设计思路

(1)使用两个定时器，T0用于PWM波翻转，T1用于调整占空比，均采用16位计时模式，因为51单片机在此模式下不能自动重装初值，因此需要在每一次触发中断后手动重装初值，为了不造成太大误差，重装初值程序需要写在中断最前面，PWM波占空比在5s内先由0%增加到100%，再逐渐减少到0%，为了保证呼吸灯呼吸均匀，决定每次以2.5%的增幅改变占空比，共改变80次;

(2)T0每25us中断一次，当累计中断80次(25×80=2000us,保证周期为2ms)时PWM波翻转;T1用于调整占空比，每12.5ms中断一次，当累计中断5次(12.5×5=62.5ms,5s/80=62.5ms)时改变占空比;

2.电路设计

(1)原理图

(2)PCB图

(3)3D模型图

3.程序源码

#include < reg52.h >
unsigned char XUNHUAN = 0;
unsigned char PWM_COUNT = 0;​​​​ //PWM翻转计时
unsigned int HUXI_COUNT = 0;​​​​​ //占空比调节计时
signed char PWM_VALUE = 2;​​​​​ //占空比比对值
unsigned char ljk = 0;​​​​​​​​ //控制占空比调整比对值direc_flag
bit direc_flag = 0;​​​​​​​​​​ //占空比调节比对值，0为增加，1为减少
sbit LED = P1 ^ 3;​​​​​​​​​​​ //定义呼吸灯接口
void timer0_init() {
    TMOD = 0x11;
    TH0 = (65536 - 46) / 256;
    TL0 = (65536 - 46) % 256;
    TH1 = (65536 - 11520) / 256;
    TL1 = (65536 - 11520) % 256;
    EA = 1;
    ET0 = 1;
    ET1 = 1;
    TR1 = 1;
    TR0 = 1;
    PWM_COUNT = 0; //初始化定时器
}
void time0()​​​​​​​​​​interrupt 1 {
    TH0 = (65536 - 46) / 256;
    TL0 = (65536 - 46) % 256;
    PWM_COUNT++;
    if (PWM_COUNT == PWM_VALUE) {
        LED = 1;
    }
    if (PWM_COUNT == 40) {
        LED = 0;
        PWM_COUNT = 0;
    }
}
void time1()​​​​​​interrupt 3 {
    TH1 = (65536 - 11520) / 256;
    TL1 = (65536 - 11520) % 256;
    HUXI_COUNT++;
}
void main() {
    LED = 1;
    while (1) {
        XUNHUAN = 1;
        if (HUXI_COUNT == 5 && direc_flag == 0) {
            HUXI_COUNT = 0;
            PWM_VALUE = PWM_VALUE + 2;
            ljk++;
        }
        if (ljk == 40) direc_flag = 1;
        if (HUXI_COUNT == 5 && direc_flag == 1) {
            HUXI_COUNT = 0;
            PWM_VALUE = PWM_VALUE - 2;
            ljk++;
        }
        if (ljk == 80) {
            direc_flag = 0;
            ljk = 0;
            PWM_VALUE = 2;
        }
    }
}