#include <SPI.h>
#include <SD.h>
#include <Wire.h>


// Data logger for the Arduino UNO computer
// This version logs data to the SD card after each set of data is taken

// the number of samples to be taken and averaged, at each z-location of the detector
const int numSamples = 20;        /* total number of samples to be taken;
                                  defining the integer variable 'numSamples' by declaring it to be a constant
                                  ensures that no other part of the program will change it from this value */

// how many milliseconds between sampling data and logging it. 1000 ms is once a second
const int sampleInterval = 100;  /* msec between data samples;
                                  defining the integer variable 'sampleInterval' by declaring it to be a constant
                                  ensures that no other part of the program will change it from this value */

#define ECHO_TO_SERIAL 1     // echo data to serial port; set to 0 if you don't want to echo data to the serial monitor
#define WAIT_TO_START 1      // Wait for serial input in setup(); set to 0 if you don't want to use a keyboard entry to begin data taking

char ch;  // Holds incoming character from the serial monitor
int z;      // starting z-position of the detector

// The analog pin that is connected to the sensor
const int photocellPin = 2;  // analog pin 2
int photocellReading = 0;

// the Adafruit data logging shield uses digital pin 10 for the SD card CS ("chip select") pin
const int chipSelect = 10;

// the logging file
File logfile;

// Error handling function
void error(char *str)
{
  Serial.print("error: ");  // prints the word "error" to the serial monitor
  Serial.println(str);      // prints the error message to the serial monitor along with a carriage return
  while(1);    // this condition would always be true, causing the program to stop here
}

// ============================================================
void setup()
{
  Serial.begin(9600);
  Serial.println();
/*  analogReference(EXTERNAL);   sets the reference (maximum) voltage for the built-in 10-bit analog-to-digital converter
                              to be the voltage applied to the AREF pin.  As previously defined by the variable 'aref_voltage'
                              this will be set to +5V.  In turn, this "maps" the 10-bit range of the ADC to 0-5V:  
                              digital '0' corresponds to 0V, and digital '1023' corresponds to 5V.  */

  pinMode(10,OUTPUT);
  
   if (!SD.begin(chipSelect))
    {
    error("Card failed, or not present");
    }

// set up the filename on the SC card to log data to
// it will be a CSV "comma-separated-value" format so Excel can easily read the data into separate columns
  char filename[] = "LOGGER00.CSV";
  for (uint8_t i = 0; i < 100; i++)
  {
    filename[6] = i/10 + '0';
    filename[7] = i%10 + '0';
    if (! SD.exists(filename))
      {
      // only open a new file if it doesn't exist
      logfile = SD.open(filename, FILE_WRITE); 
      break;  // leave the loop!
      }
   }
  
  if (! logfile)
    {
    error("couldn't create file");
    }
  
  Serial.print("Logging to: ");
  Serial.println(filename);
  logfile.println("z,LIGHT");    // prints this text to the logging file
  #if ECHO_TO_SERIAL
    Serial.println("z,LIGHT");   // prints the same text to the serial monitor (if ECHO_TO_SERIAL is set to 1 TRUE)
  #endif //ECHO_TO_SERIAL
  
  Serial.println("Enter new z-value:");
 }    // end of the SETUP function

// ========================================================================

/* THE MAIN PROGRAM */
void loop()
{
  if(Serial.available()>0)
    {
  ch = Serial.peek();
      if((ch == 'e')||(ch == 'E'))
      {
      logfile.flush();
      Serial.print("Data Taking Completed");
      while(1);
      }
      z = Serial.parseInt();
      if(Serial.read() == '\n')
      {
      Serial.print("z = ");
      Serial.print(z);
      Serial.print("     ");
      for (int i = 0; i < numSamples; i ++)
      {
        analogRead(photocellPin);
        delay(10); // a 10ms delay
        photocellReading = photocellReading + analogRead(photocellPin);  
      }
    photocellReading = photocellReading/numSamples;     
    
  Serial.print("Det. Avg. = ");
  Serial.print(photocellReading);
  Serial.println();
    
  logfile.print(z);
  logfile.print(", ");    
  logfile.print(photocellReading);
  logfile.println();    // adds a carriage return ('new line') to the data stream   
      }
  Serial.println("Enter new z-value:");
   }

}