User submitted example for a HC-SR04 Ultrasonic Sensor
#define echoPin 7 // Echo Pin
#define trigPin 8 // Trigger Pin
long duration, distance; // Duration used to calculate distance
void setup()
{
Serial.begin (9600);
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
}
void loop()
{
/* The following trigPin/echoPin cycle is used to determine the
distance of the nearest object by bouncing soundwaves off of it. */
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
duration = pulseIn(echoPin, HIGH);
//Calculate the distance (in cm) based on the speed of sound.
distance = duration/58.2;
Serial.println(distance);
//Delay 50ms before next reading.
delay(50);
}