#define TRIG_PIN 4  
#define ECHO_PIN 5  
#define LED_PIN 1 
  
void setup() {  
  pinMode(TRIG_PIN, OUTPUT);  
  pinMode(ECHO_PIN, INPUT);  
  pinMode(LED_PIN, OUTPUT);  
  Serial.begin(9600);  
}  
  
void loop() {  
  long duration, distance;  
    
  digitalWrite(TRIG_PIN, LOW);  
  delayMicroseconds(2);  
  digitalWrite(TRIG_PIN, HIGH);  
  delayMicroseconds(10);  
  digitalWrite(TRIG_PIN, LOW);  
    
  duration = pulseIn(ECHO_PIN, HIGH);  
  distance = (duration / 2) / 29.1;  // 计算距离，单位：cm  
  
  if (distance < 10 || distance == 0) {  
    digitalWrite(LED_PIN, HIGH);  // 距离小于10cm或无法测量到距离（可能为0），LED亮起  
  } else {  
    digitalWrite(LED_PIN, LOW);  // 距离大于10cm，LED熄灭  
  }  
  
  Serial.print("Distance: ");  
  Serial.println(distance);  
 delay(500);  
}