// 定义3个LED引脚
const int ledPin1 = 2;
const int ledPin2 = 3;
const int ledPin3 = 4;

// 设置呼吸灯的最小和最大亮度
int minBrightness = 0;
int maxBrightness = 255;

// 设置呼吸灯的步长和延时时间
int fadeStep = 5;
int delayTime = 10;

void setup() {
  // 设置LED引脚为输出模式
  pinMode(ledPin1, OUTPUT);
  pinMode(ledPin2, OUTPUT);
  pinMode(ledPin3, OUTPUT);
}

void loop() {
  // 依次控制3个LED灯的呼吸效果
  fadeLED(ledPin1);
  fadeLED(ledPin2);
  fadeLED(ledPin3);
}

// 控制单个LED灯的呼吸效果
void fadeLED(int pin) {
  // 逐渐增加亮度
  for (int brightness = minBrightness; brightness <= maxBrightness; brightness += fadeStep) {
    analogWrite(pin, brightness);
    delay(delayTime);
  }

  // 逐渐减小亮度
  for (int brightness = maxBrightness; brightness >= minBrightness; brightness -= fadeStep) {
    analogWrite(pin, brightness);
    delay(delayTime);
  }
}