#include SoftwareServo.h 
const int TRIG_PIN = 4; 
const int ECHO_PIN = 3; 
const int SERVO_PIN = 0; 
const int DISTANCE_THRESHOLD = 10; // centimeters
SoftwareServo servo; 
float duration_us, distance_cm;
void setup() {
// Serial.begin (9600); 
pinMode(TRIG_PIN, OUTPUT); 
pinMode(ECHO_PIN, INPUT); 
servo.attach(SERVO_PIN); 
servo.write(0);
}
void loop() {
// generate 10-microsecond pulse to TRIG pin
digitalWrite(TRIG_PIN, HIGH);
delayMicroseconds(10);
digitalWrite(TRIG_PIN, LOW);
// measure duration of pulse from ECHO pin
duration_us = pulseIn(ECHO_PIN, HIGH);
// calculate the distance
distance_cm = 0.017 * duration_us;
if(distance_cm < DISTANCE_THRESHOLD)
servo.write(90); // rotate servo motor to 90 degree
else
servo.write(0); // rotate servo motor to 0 degree
}