#include <SPI.h>            // include SPI library
#include <SD.h>             // include SD library
File file;                  // #associate file with SD library
int CSpin = 10;             // #chip select pin for SD card
String filename;
String basefile = "data";   // #default filename is data.csv
bool filefound = false;
int filecount = 0;          // #for incrementing filename
int count = 0;
String data;                // data to write to SD card
void setup()
{
  Serial.begin(9600);       // #define Serial output baud rate
  if(SD.begin(CSpin) == 0)
  {
    Serial.println("Card fail");  // #return to void loop() if SD card not found
    return;
  }
  Serial.println("Card OK");
  filename=basefile + ".csv";   // generate filename
  while (filefound == 0)        // #search for file with filename
  {
    if(SD.exists(filename)>0)   // #if filename exists on SD card,
    {                           // #then increment filename counter
      filecount++;              // generate new filename
      filename = basefile + String(filecount) + ".csv";
    }
    else filefound = true; // #flag file with filename located on SD card
  }
  file = SD.open(filename, FILE_WRITE);   // #open file on SD card
  if(file == 1)
  {
    Serial.print(filename);Serial.println(" created");
    data = "Count";             // column header
   file.println(data);         // #write column header to file
    file.close();               // #close file after writing to SD card
  }
  else Serial.println("Couldn't access file"); // file not opened
}
void loop()
{
  count = count + 1;            // #incremental counter
  data = String(count);         // #convert counter to string
  File file = SD.open(filename, FILE_WRITE); // #open file on SD card
  if(file == 1) file.println(data);   // #write data string to file on SD card
  file.close();                       // #close file on SD card
  delay(1000);                        // #delay 1s before next count
}