LightningTrigger

const int triggerOut = 9;               // Output to camera shutter release (to take picture)
const int sensor = A0;                  // Photoresistor
const float lightLevelMultiplier = 1.4; // level above ambient to trigger shutter release (ex. 1.4 = 40% above ambient)
int lightLevel = 0;                     // holds reading from photoresitor
int ambient = 0;                        // holds average of last 'numReadings' samples of lightLevel to determine ambient light level

//bellow are variables used for calculating ambient light
const int numReadings = 100;    // number of readings we want to average
int readings[numReadings];      // the readings from the photoresistor input
int readIndex = 0;              // the index of the current reading
long total = 0;                 // the running total

void setup() {
  // put your setup code here, to run once:

Serial.begin(115200);
pinMode(triggerOut,OUTPUT);
digitalWrite(triggerOut,HIGH);    // Setting shutter release output to HIGH (LOW is "ON")

}


void loop() {

  lightLevel = analogRead(sensor);      // reading the current light level

  // calculate ambient lighting
  total = total - readings[readIndex];      // something i stole and do not understand well enough to comment
  readings[readIndex] = analogRead(sensor); //
  total = total + readings[readIndex];      //
  readIndex = readIndex + 1;                //
                                            //
  if (readIndex >= numReadings) {           //
    readIndex = 0;                          //
  }                                         //


  ambient = total / numReadings; // average




if(lightLevel > ambient * lightLevelMultiplier){  // checks for spike in light level (lightning)
  digitalWrite(triggerOut,LOW);                   // Turn "on" shutter release
  delay(10);                                      // small delay just seemed appropriate
  digitalWrite(triggerOut,HIGH);                  // Turn "off" shutter release
  delay(150);                                     // Delay to filter out multiple triggers for single event

}

Serial.print("Ambient: ");                    // For debugging
Serial.print(ambient);
Serial.print("  ");
Serial.print("lightLevel: ");
Serial.println(lightLevel);
Serial.print("readings[numReadings]: ");
Serial.print(readings[numReadings]);
Serial.print(" readIndex: ");
Serial.print(readIndex);
Serial.print(" total: ");
Serial.println(total);
Serial.println();


}