ultrasonic sensor and power relay to control desk lighting

relaylight.ino

/* 

Using an Arduino with a Power Relay

Parts used:
--ultrasonic sensor
--desk lamp
--Arduino Uno
--120v relay

This sketch uses an ultrasonic sensor to detect whether
a person in near or sitting at a desk, and sends a 
signal to a power relay to turn desk lighting on or off.

*/
#include <NewPing.h>

const int LIGHT = 10;
const int TRIGGER = 12;
const int ECHO = 11;

NewPing sonar(TRIGGER, ECHO);

void setup(){
  pinMode(LIGHT, OUTPUT); 
}

/* The main loop iterates every 2.5 seconds. */

void loop(){
    
  /*In order to get a accurate measure of wether
  someone is near, we read the ultrasonic sensor
  30 times and take the average. That way, if the
  ultrasonic sensor reads sporadically as it 
  occasionaly does, those values will be averaged out.  
  This takes 0.05 * 30 = 1.5 seconds to get a value
  from the sensor. */
  
  while (int i, i < 30, i++){
    sum = sum + sonar.ping_cm();
    delay(50);
  }
  int average_distance = sum/30; 
  
  
  /* Using the value, we send a signal to the relay
  depending on whether someone is detected less than 
  130 cm away. We also pause for a second for good 
  measure. */
  
  if (average_distance < 130){
    digitalWrite(LIGHT, HIGH);
    delay(1000);
  }
  
  else{   
    digitalWrite(LIGHT, LOW);
    delay(1000);
  }
}