/*
 * Simple photoresistor-based motion detector
 * 
 * This project is part of Accrochages
 * See http://accrochages.drone.ws
 * 
 * (c) 2008 Sofian Audry (info@sofianaudry.com)
 * (c) 2008 Samuel St-Aubin (samuel.staubin@gmail.com)
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#define PHOTO_IN 0  // Photoresistor input.
#define LED_OUT 13  // Led output (for demonstration).

#define THRESHOLD 3 // Threshold (needs to be set by hand).

/*
 * This function returns the motion, calculated as the difference between 
 * two readings of the photoresistor. Motion is expressed as an integer
 * between -1023 and 1023.
 */
int motion(long time = 100) {
  int before = analogRead(PHOTO_IN);
  delay(time);
  return (analogRead(PHOTO_IN) - before);
}

void setup() {
  pinMode(LED_OUT, OUTPUT);
  digitalWrite(LED_OUT, LOW);
}

void loop() {
  int m = motion();
  if (abs(m) > THRESHOLD)
    digitalWrite(LED_OUT, HIGH);
  else
    digitalWrite(LED_OUT, LOW);
}