获取为超声波传感器计算的距离0

Question

我正在为具有障碍物和边缘避免机制的无线遥控机器人编写代码。因此，这里我们用移动设备控制机器人，现在如果障碍物在它前面或它即将从高处掉落，它将避开它。为了避开障碍物，我使用了HC-05超声波传感器。但是我得到的距离是超声波传感器零。为什么？ `

#include<Servo.h>
Servo myservo;
const int trigPin = 2;
const int echoPin = 4;
String voice;
long duration;
int distance;
int 
M11 = 13,
M12 = 12,
M21 = 11, 
M22 = 10; 
void stay(){
 digitalWrite(M11, LOW);
 digitalWrite(M12, LOW); 
 digitalWrite(M21, LOW);
 digitalWrite(M22, LOW); 
 }
void forward() {
 digitalWrite(M11, HIGH);
 digitalWrite(M12, LOW); 
 digitalWrite(M21, HIGH);
 digitalWrite(M22, LOW); 

 }

void backward(){
  digitalWrite(M11, LOW);
  digitalWrite(M12, HIGH); 
  digitalWrite(M21, LOW);
  digitalWrite(M22, HIGH); 

}
void left(){
  digitalWrite(M11, LOW);
  digitalWrite(M12, LOW); 
  digitalWrite(M21, HIGH);
  digitalWrite(M22, LOW); 
  delay(1000);
  digitalWrite(M11,HIGH);

}
void right(){
  digitalWrite(M11, HIGH);
  digitalWrite(M12, LOW); 
  digitalWrite(M21, LOW);
  digitalWrite(M22, LOW); 
  delay(1000);
  digitalWrite(M21,HIGH);

 }
 int dist()
   {
     digitalWrite(trigPin, LOW);
     delayMicroseconds(2);
     digitalWrite(trigPin, HIGH);
     delayMicroseconds(10);
     digitalWrite(trigPin, LOW);
     duration = pulseIn(echoPin, HIGH);
      // Calculating the distance
     distance= duration*0.034/2;  
     Serial.println(distance);
     return distance;
 }

 void Avoid(int d)
 {
   int d1,d2;

   if(d<18 || (digitalRead( 9)==1) || (digitalRead( 8)==0))
    {

     stay();
     delay(500);
     backward();
     delay(650);
     stay();
     myservo.write(25);

    d1=dist();
    delay(650);
    myservo.write(90);
    delay(500);
    myservo.write(180);
    d2=dist();
    delay(650);
    myservo.write(140);
    if(d1>d2)
    {
      left();
      delay(800);
    }
    else
    {
      right();
     delay(800);
    }

 }
}

void setup() {
   Serial.begin(9600);
   myservo.attach(7);
   pinMode(8,INPUT);
   pinMode(9,INPUT);
   pinMode(M11, OUTPUT); 
   pinMode(M12, OUTPUT); 
   pinMode(M21, OUTPUT); 
   pinMode(M22, OUTPUT); 
 }

 void loop() {

  int d,d1,d2;
  d=dist();
  Serial.println("D:");
  Serial.println(d);
  myservo.write(140);
  while (Serial.available())
    {  //Check if there is an available byte to 
                                  read
    delay(10); //Delay added to make thing stable 
    char c = Serial.read(); 
    if (c == '#') {break;} 
         voice += c; 
    }  

 if (voice.length() > 0) {
     Serial.println(voice); 

       if(voice == "forward") {forward();}  //Move Robot Forward (Call 
                                             Function)
       else if(voice == "backward"){backward();} //Move Robot Backward 
                                                 (Call Function)
       else if(voice == "left"){left();} //Move Robot Left (Call 
                                                 Function)
       else if(voice == "right"){right();} //Move Robot right (Call 
                                           Function)
       else if(voice == "stop"){stay();} //Stop Robot (Call Function)


       voice="";
     }
    Avoid(d);
  }