int echoPin=6;
int trigPin=7;//set up ultrasound pins on HC-SR04
int led = 13;//assign LED pin
int threshold = 25;
//assign threshold distance

void setup() {

Serial.begin (9600); //open serial communications
pinMode(trigPin, OUTPUT);
pinMode (echoPin, INPUT);
pinMode(led, OUTPUT);

//describe inputs and outputs

}

void loop () {

int duration, cm;
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite (trigPin, HIGH);
delayMicroseconds (10);
digitalWrite(trigPin, LOW);
duration= pulseIn(echoPin, HIGH);
cm= duration /29 /2;

Serial.print(cm);
Serial.println("cm");
delay(100);
 
if (cm > threshold) {
digitalWrite(led, HIGH); //turn on LED
}
else {
digitalWrite(led,LOW); //otherwise turn it off
}
}

-------------------------------------------------------------------------

  /*
HC-SR04 Ping distance sensor]
VCC to arduino 5v GND to arduino GND
Echo to Arduino pin 13 Trig to Arduino pin 12
Red POS to Arduino pin 11
Green POS to Arduino pin 10
560 ohm resistor to both LED NEG and GRD power rail
More info at: http://goo.gl/kJ8Gl
Original code improvements to the Ping sketch sourced from Trollmaker.com
Some code and wiring inspired by http://en.wikiversity.org/wiki/User:Dstaub/robotcar
*/

#define trigPin 13
#define echoPin 12
#define led 11
#define led2 10

void setup() {
Serial.begin (9600);
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
pinMode(led, OUTPUT);
pinMode(led2, OUTPUT);
}

void loop() {
long duration, distance;
digitalWrite(trigPin, LOW); // Added this line
delayMicroseconds(2); // Added this line
digitalWrite(trigPin, HIGH);
// delayMicroseconds(1000); - Removed this line
delayMicroseconds(10); // Added this line
digitalWrite(trigPin, LOW);
duration = pulseIn(echoPin, HIGH);
distance = (duration/2) / 29.1;
if (distance < 4) { // This is where the LED On/Off happens
digitalWrite(led,HIGH); // When the Red condition is met, the Green LED should turn off
digitalWrite(led2,LOW);
}
else {
digitalWrite(led,LOW);
digitalWrite(led2,HIGH);
}
if (distance >= 200 || distance <= 0){
Serial.println("Out of range");
}
else {
Serial.print(distance);
Serial.println(" cm");
}
delay(500);
}