Ultraonic sensor not working properly

[gwynethchiew]

//define Pins
int led = 13;
int trigPin = 9;
int echoPin = 8;

// defines variables
long duration;
int distance;

void setup() 
{
  //Sets the Led as an Output
pinMode(led, OUTPUT);
// Sets the trigPin as an Output
pinMode(trigPin, OUTPUT);
// Sets the echoPin as an Input 
pinMode(echoPin, INPUT);
// Starts the serial communication 
Serial.begin(9600); 
}
void loop() 
{
// Clears the trigPin
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
// Sets the trigPin on HIGH state for 10 micro seconds
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
// Reads the echoPin, returns the sound wave travel time in microseconds
duration = pulseIn(echoPin, HIGH);
// Calculating the distance
distance= duration*0.034/2;
// Prints the distance on the Serial Monitor
Serial.print("Distance: ");
Serial.println(distance);
if ( distance <= 14 ) // Change Distance according to Ultrasonic Sensor Placement
 {
digitalWrite (led , HIGH );
delay (5000);
 } 
else 
{
digitalWrite (led, LOW );
 }

}

As shown in the code, the LED is supposed to light only when there's something in front of it with the distance less than the value that I have set.

This is the reading read by the ultrasonic sensor, but there was nothing in front of it.

What is the problem? I tried using another ultrasonic sensor, but the result is still the same.

[Terrypin]

What is the source of your sketch?

On a brief look I saw no code in it showing where the sensor gets its input from? Shouldn't it have an #include library.h statement?

[gilshultz]

Is the sensor pointing to infinity? There has to be something in front of it, the Sky, Wall, etc.

[gwynethchiew]

To be exact, it's facing the ceiling the whole time

[gwynethchiew]

What do you mean exactly? This is my first time using this.

[DaveEvans]

One problem is that there should be a delay of about 30 to 50 milliseconds between every ping, to allow echos to die. Otherwise, the poor thing gets confused.

In your code, there will only be a significant delay between pings if distance is <= 14 (other than the delay caused by printing to serial at the glacially slow 9600 baud).

Try adding a delay here:

{
   digitalWrite (led, LOW );
   delay (50); //<<--------------------- 
  }