It's an Arduino experiment to count how many times Mia (my cat) eats per day, if she eats more on the week or weekend when we are at home. http://f.cl.ly/items/3E3Q3p2x2S132e1T2332/Image%202012.10.27%201:05:59%20PM.png

mia_eating.ino

#include "Ultrasonic.h"
#include <SD.h>

Ultrasonic ultrasonic(7,6);

File file;

boolean eating = false;

int hour = 23; 
int minu = 0;
int sec = 0;
int day = 29;
int sleepmili = 10000;
// initialDistance will be defined after the first minute that the Arduino is turned on. Mia is eating If the current distance (currDistance) is less than initialdistance.
int initialDistance = 0;
int countInitialDistance = 0;
// safeDistance is a small safe distance to guarantee if the mia's food move up.
int safeDistance = 5;

//------------------------------------------------------------------------------
void setup() {
  Serial.begin(9600);
  if (!SD.begin()) {
    Serial.println("sd begin failed");
    return;
  }
}

void updateDateTime(){
  sec += sleepmili / 1000;
  if(sec > 60){
    sec = sleepmili / 1000;
    minu++;
    if(minu > 60){
      minu = 1;
      hour++;
      if(hour > 24){
        hour = 1;
        day++;
        if(day > 30){
          day = 1;
        }
      }
    }
  }
}

boolean isEating(int currDistance){
  return currDistance < initialDistance && !eating;
}

boolean stoppedEating(int currDistance){
  return currDistance > initialDistance && eating;
}

boolean isDefiningInitialDistance(int currDistance){
    if(initialDistance == 0){
      countInitialDistance += 1;
      if(countInitialDistance == 6){
        initialDistance = currDistance - safeDistance;
      }
    }
    return initialDistance == 0;
}

//------------------------------------------------------------------------------
void loop()
{
  
  updateDateTime();
  
  int currDistance = ultrasonic.Ranging(CM);
  
  if(!isDefiningInitialDistance(currDistance)){
    if(isEating(currDistance)){
      logEating(currDistance, "Mia eating");
      eating = true;
    } else if(stoppedEating(currDistance)) {
      logEating(currDistance, "Mia stop eating");
      eating = false;
    }
  }
  
  delay(sleepmili);
}

void logEating(int currDistance, char *msg){
  
    file = SD.open("eating.txt", FILE_WRITE);
    file.print(day);
    file.print(" - ");
    file.print(hour);
    file.print(":");
    file.print(minu);
    file.print(",");
    file.print(msg);
    file.print(",");
    file.print(currDistance);
    file.println("cm");
    file.close();
  
    // Debug output
    Serial.print(day);
    Serial.print(" - ");
    Serial.print(hour);
    Serial.print(":");
    Serial.print(minu);
    Serial.print(",");
    Serial.print(msg);
    Serial.print(",");
    Serial.print(currDistance);
    Serial.println("cm");
}

Ops... working url: http://f.cl.ly/items/3E3Q3p2x2S132e1T2332/Image%202012.10.27%201:05:59%20PM.png