ultrasonic_arduino.c

#define EPin 7 // Echo Pin
#define TPin 8 // Trigger Pin
#define LPin 9 // LED

int maxD = 200;
int minD = 0;
long duration, distance;

void setup() 
{
 Serial.begin (9600);
 pinMode(TPin, OUTPUT);
 pinMode(EPin, INPUT);
 pinMode(LPin, OUTPUT);
}

void loop() 
{
 digitalWrite(TPin, LOW); 
 delayMicroseconds(2); 

 digitalWrite(TPin, HIGH);
 delayMicroseconds(10); 
 
 digitalWrite(TPin, LOW);
 duration = pulseIn(EPin, HIGH);
 
 distance = duration/58.2;
 
 if (distance >= maxD || distance <= minD)
 {
   Serial.println("-1");
   digitalWrite(LPin, HIGH); 
 }
 else 
 {
   Serial.println(distance);
   digitalWrite(LPin, LOW); 
 }
 
 delay(50);
}