void setup() {
  pinMode(5,OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int a = analogRead(A0);               //读取模拟输出引脚A0
  int brightness = map(a,0,1023,0,255); //等比函数
  Serial.println(brightness);
  analogWrite(5, brightness);
  delay(100);
}