int minlight=0;//定义最小亮度
int maxlight=255;//定义最大亮度
float breathstep=0.5;//定义亮度变化值
int delaytime=1;//定义亮度保持时间

void setup()//接上3个LED
{
  pinMode(3, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(6, OUTPUT);
}

void loop()//3个LED亮度依次变化
{
  breathing(3);
  breathing(5);
  breathing(6);
}

void breathing(int pincode)
{
  for(float light=0;light<=maxlight;light=light+breathstep)//逐渐变亮，到最亮
  {
    analogWrite(pincode,light);
    delay(delaytime);
  }

  for(float light=225;light>=minlight;light=light-breathstep)//逐渐变暗，到最暗
  {
    analogWrite(pincode,light);
    delay(delaytime);
  }
}