MotionActivatedLightSwitch.ino

/*
 * MotionActivatedLightSwitch.ino
 *
 * Created: 20/12/2012 4:38:29 PM
 *  Author: grist.carrigafoyl
 *  Target: Arduino Uno

 Activate a pin when motion is detected via a PIR sensor on another pin.
 Checks ambient light level via a photoresistor and only activates if the light level is low


 */

#define PHOTORESISTOR           1  // Analog in
#define PIR_PIN         8  // Digital in
#define SWITCH_PIN      13 // Digital out

// The light level below which the switch will trigger.
#define LOW_LIGHT_LEVEL     300 // Based on experimentation.


// Prototypes
int read_adc(char pin);

void setup()
{
  pinMode(PIR_PIN, INPUT);
  pinMode(SWITCH_PIN, OUTPUT);

}

void loop()
{
      byte pir_state;
      int curr_light_level;

      // How long the light stays on for. Simple constant for now
      int delay_time = 5000;

      // Loop forever
      for (;;) {
            pir_state = digitalRead(PIR_PIN);
            if (pir_state == LOW) {  // Movement detected (pin is pulled high normally)
                curr_light_level = read_adc(PHOTORESISTOR);
                if (curr_light_level < LOW_LIGHT_LEVEL) {
                    digitalWrite(SWITCH_PIN, HIGH);  // On
                    delay(delay_time);
                }
            }
            digitalWrite(SWITCH_PIN, LOW); // Off
        }
}

int read_adc(char pin)
{ // Read the analog value from the ADC input pin.
    int ret_val;

    ret_val = analogRead(pin);
    return(ret_val);
}