Average of reading on IR sensor

Other Hardware Sensors
12 
// http://arduino.cc/forum/index.php/topic,56396.0.html
// and
// http://arduino.cc/forum/index.php/topic,74895.0.html

/*
  Sketch to demonstrate how to decrease time of analog read.
 it shortens the delay by manipulating registers and reducing the prescale
 timer value from 128 to 16;
 
 Note Serial Speed! Change to suit yourself!
 
 Sample Sketch From Arduino Cookbook by Margolis (O'Reilly Press)
 Modified by Willr March24, 2011 
 
 Tested on Mega2560 Arduino board with an MA7361 Z output hooked to 
 Sensor 5
 */

// CHANGE Sensor Pin to suit yourself...
const int sensorPin = 5;

// Change  number of entries to a value divisible by 100 only
const int numberOfEntries = 100;

unsigned long microseconds;
unsigned long duration1;
unsigned long duration2;

int results[numberOfEntries];

void setup()
{
  Serial.begin(9600); ///CHANGED
  Serial.flush();


  // standard analog read performance -- prescale == 128
  microseconds = micros();
  for (int i=0; i < numberOfEntries; i++)
  {
    results[i] = analogRead(sensorPin);
  } 

  duration1 = micros() - microseconds;

  Serial.print(numberOfEntries);
  Serial.print("   readings took ");
  Serial.println(duration1);

  // This double loop just prints a neat table..
  for( int j=0; j < numberOfEntries; j=j+20)
  {
    for (int i=0; i < 20; i++) 
    {
      Serial.print(results[j+i]);
      Serial.print(",  ");
    } //end loop i
    Serial.println();
  } //end loop j

  Serial.println();

  // prescale clock to 16
  bitClear(ADCSRA,ADPS0);
  bitClear(ADCSRA,ADPS1);
  bitSet(ADCSRA,ADPS2);

  // Performance with Changeed Prescale...
  microseconds = micros();
  for (int i=0; i < numberOfEntries; i++)
  {
    results[i] = analogRead(sensorPin);
  } 

  duration2 = micros() - microseconds;
  Serial.print(numberOfEntries);
  Serial.print("   readings took ");
  Serial.println(duration2);

  for( int j=0; j < numberOfEntries; j=j+20)
  {
    for (int i=0; i < 20; i++)
    {
      Serial.print(results[j+i]);
      Serial.print(",  ");
    } //end loop i
    Serial.println();
  } //end loop j

  Serial.println();

  Serial.print("Ratio of read times is : ");
  Serial.println((float)duration1/duration2);
  Serial.println("********************");
}

void loop()
{
  // empty main loop is deliberate...
}

There are also optimizations known if the pin number is hard coded at compile time - could not find and example though -