<code cpp>
/********************************************************
*  Code to relay the data from one PIR sensor to the PC
*  using a simple low-pass filter (weighted average).
*  By: Jonathan Mash
*  Date: Feb. 2009
*********************************************************/

#define PIR_HIST 5
int PIR_idx;
int PIR_one[PIR_HIST];


void setup()
{
  Serial.begin(9600);
  
  PIR_idx = 0;
}


void loop()
{
  Record();

  Serial.println(PIR_one[PIR_idx]);
  
  PIR_idx++;
  if(PIR_idx == PIR_HIST)
    PIR_idx = 0;
  delay(50);
}

void Record()
{
  int i = PIR_idx;

  PIR_one[PIR_idx] = (int)floor(analogRead(0)*0.75);
  
  if(i == 0)
    i = PIR_HIST-1;
  else
    i = i-1;
  PIR_one[PIR_idx] += (int)floor(PIR_one[i]*0.125);

  if(i == 0)
    i = PIR_HIST-1;
  else
    i = i-1;
  PIR_one[PIR_idx] += (int)floor(PIR_one[i]*0.1);
  
  if(i == 0)
    i = PIR_HIST-1;
  else
    i = i-1;
  PIR_one[PIR_idx] += (int)floor(PIR_one[i]*0.025); 
}
</code>