#include <SPI.h>                    // include SPI library
#include <SD.h>                     // include SD library
File file;                          // #associate file with SD library
String filename = "data.csv";       // filename
int CSpin = 10;                     // chip select pin
int lightPin = A0;                  // LDR light intensity pin
int tempPin = A1;                   // temperature sensor pin
int i = 0;                          // data record counter
int light;
float temp;
String data;
void setup()
{
  Serial.begin(9600);                  // #define Serial output baud rate
  Serial.println("checking SD card");  // #print message to Serial Monitor
  if(SD.begin(CSpin) == 0)             // #check for presence of SD card
  {
    Serial.println("Card fail");  // #return to void setup() if SD card not found
    return;
  }
  Serial.println("Card OK");
  if(SD.exists(filename)>0) SD.remove(filename); // #delete existing file
  file = SD.open(filename, FILE_WRITE);    // create new file
  if(file == 1)                            // file opened
  {
    String header = "i, light, temp";  // create column headers
    file.println(header);         // #write column header to SD card
    file.close();                 // #close file after writing to SD card
  }
  else Serial.println("Couldn't access file");  // #file not opened
}
void loop()
{
  i++;                  // #increase data record counter
  Serial.print("record ");Serial.println(i); // #print record number
  light = analogRead(lightPin);               // light reading
  temp = (500.0*analogRead(tempPin))/1023;    // #temp reading
                        // referenced to 5V create string from readings
  data = String(i) + "," + String(light) + "," + String(temp);
  file = SD.open(filename, FILE_WRITE);  // #open data file before writing
  file.println(data);   // #write data string to file
  file.close();         // #close file after writing to SD card
  delay(5000);          // #delay 5s before next reading
}