#include <SD.h>
File sdcard_file;
int CS_pin = 10; // Pin 10 on Arduino
void setup(){
  // put your setup code here, to run once:
  pinMode(A0, INPUT);
  pinMode(CS_pin, OUTPUT);
  Serial.begin(9600);
  // SD Card Initialization
  if (SD.begin()){
    Serial.println("SD card is ready to use.");
  }
  else {
    Serial.println("SD card initialization failed");
    return;
  }
}

void loop(){
  // put your main code here, to run repeatedly
  sdcard_file = SD.open("data.txt", FILE_WRITE);
  if (sdcard_file) { 
    long PotValue = analogRead(A0);
    long PotVPercent = ((PotValue*100)/1023);
    //Serial.println(PotValue);
    Serial.print(PotVPercent);
    Serial.println(" %");
    sdcard_file.print(PotVPercent);
    sdcard_file.println(" %");
    sdcard_file.close();
  }
  // if the file didn't open,
  else {
    Serial.println("error opening test.txt");
  }
  delay(1000);
}