Millis() timer

sorry!, here is my code:

/*

Project Arduino, FINAL V1.0 3 Sensors,Time&Date,FTP,SD,Errorlog

-  Leest temperatuur en vochtigheid uit met behulp van SHT11 temperatuur/vochtigheid sensoren van Sensirion
-  Slaat de logdata op SD op en verzend deze naar een FTP server
-  Tijd word opgehaald van NTP server en gebruikt in de errorlog en logfile
-  Filenaam om de Arduino te indentificeren instellen door het TXT bestand filename aan te passen op de SD kaart
-  Errorlog word op de SD opgelsagen onder de naam ERRORLOG.TXT

By: Jan Verhoeckx
*/


// INCLUDED LIBRARIES
//--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\\

//Libraries:
#include <SPI.h>         
#include <Ethernet.h>
#include <EthernetUdp.h>
#include <SD.h>
#include <Time.h>
#include <FTPsend.h>
#include <SHT1x.h>
#include <Streaming.h>



// GLOBALE VARIABELEN
//--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\\

//Pin 4 reserveren voor SD:
const int chipSelect = 4;

//Globale variabelen:
int localtimeA = 0;
int localtimeB = 0;
int localtimeC = 0;
char time[20] = {0};
char fileName[50] = {0};
float temp_c;
float humidity;
float temp_c2;
float humidity2;
float temp_c3;
float humidity3;
long previousMillis = 0; 
long interval = 1000;    

// ETHERNET INSTELLINGEN
//--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\\

// MAC adres van de Arduino
byte mac[] = {  
  0x90, 0xA2, 0xDA, 0x0D, 0x2A, 0x59 };


// PINNEN VOOR SENSOREN DEFINEREN
//--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\\

// SHT11 sensor define datapin en clockpin
#define dataPin3 8
#define dataPin2 9
#define dataPin  10
#define clockPin 11
SHT1x sht1x(dataPin, clockPin);
SHT1x sht2x(dataPin2, clockPin);
SHT1x sht3x(dataPin3, clockPin);


// BEGIN SETUP && ETHERNET VERBINDING STARTEN && VERSIE PRINTEN VIA SD
//--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\\

void setup() 
{
// Serial output:
Serial.begin(38400);
Serial.println("STX11 sensors with time, SD, Ethernet, FTP, Errorlog  --->>  By: Jan Verhoeckx  FINAL V1.0 <<---");

  
// start Ethernet en UDP connectie
  if (Ethernet.begin(mac) == 0) {
  Serial.println("Failed to configure Ethernet using DHCP");
  // Als er geen verbinding kan worden gemaamkt, niet verder gaan:
  for(;;);
  }
  
  
Serial.println("My IP address: ");
  for (byte thisByte = 0; thisByte < 4; thisByte++) {
  // print het ip over serial:
  Serial.print(Ethernet.localIP()[thisByte], DEC);
  Serial.print("."); 
  }  
  
  
//UDP begin:
Udp.begin(localPort);
 
 
// SD INITIALISEREN  
//--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\\

//SD begin:  
digitalWrite(10, HIGH);   
// Kijken of er een SD kaart aanwezig is, aangeven via serial of de SD gereed is:
  if (!SD.begin(chipSelect)) {
   Serial.println("Card failed, or not present");
   return;
  }
Serial.println("card initialized.");

}

// BEGIN LOOP && TIMER INSTELLEN OM DE MINUUT METEN
//--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\\

void loop()
{
//Om de minuut meten en de data naar de FTP server verzenden:       
  unsigned long currentMillis = millis();
 
  if(currentMillis - previousMillis > interval) {
    // save the last time you blinked the LED 
    previousMillis = currentMillis;  

// TIJD BEREKENEN VAN NTP SERVER   
//--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\\
  
  //Tijd van NTP server verkrijgen:
  
  sendNTPpacket(timeServer); // send an NTP packet to a time server

  // wait to see if a reply is available
   if ( Udp.parsePacket() ) {  
    // We've received a packet, read the data from it
    Udp.read(packetBuffer,NTP_PACKET_SIZE);  // read the packet into the buffer

    //the timestamp starts at byte 40 of the received packet and is four bytes,
    // or two words, long. First, esxtract the two words:

    unsigned long highWord = word(packetBuffer[40], packetBuffer[41]);
    unsigned long lowWord = word(packetBuffer[42], packetBuffer[43]);  
    // combine the four bytes (two words) into a long integer
    // this is NTP time (seconds since Jan 1 1900):
    unsigned long secsSince1900 = highWord << 16 | lowWord;                
    
    // Unix time starts on Jan 1 1970. In seconds, that's 2208988800:
    const unsigned long seventyYears = 2208988800UL;     
    // subtract seventy years:
    unsigned long epoch = secsSince1900 - seventyYears;    
  
    // Set time voor time librarie 
    setTime(secsSince1900 - seventyYears);

    //Bereken local time en schrijf weg naar localtimeA, B en C
    localtimeA = ((epoch % 86400L) /3600 +1);    //86400L   //9300L
    localtimeB = ((epoch  % 3600) / 60);
    localtimeC = (epoch % 60); 
  }


// SENSOREN UITLEZEN
//--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\\  
  
  // Data van de sensor uitlezen
  temp_c = sht1x.readTemperatureC();
  humidity = sht1x.readHumidity();
  //sensor2
  temp_c2 = sht2x.readTemperatureC();
  humidity2 = sht2x.readHumidity();
  //sensor3
  temp_c3 = sht3x.readTemperatureC();
  humidity3 = sht3x.readHumidity();
 
 
// LOGDATA NAAR SD SCHRIJVEN 
//--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\\

//Naam van het bestand van de SD kaart aflezen, zo word de Arduino in Hobbit geïndentificeerd.
  File FileNameonSD = SD.open("filename.txt");
  byte index = 0;
    while (FileNameonSD.available())
    {
       fileName[index++] = FileNameonSD.read();
       fileName[index] = '\0';
    }
    
  Serial.println(fileName);
  
   
  //tijd, en meetwaardes naar SD schrijven

  //verwijder oud logfile
  SD.remove(fileName);
 
  Serial.print("naar SD schrijven...");
  File dataFile = SD.open(fileName, FILE_WRITE);
  if (dataFile) {  
    if (localtimeB < 10 ) {
        dataFile << "" << "Localtime: " << localtimeA << ":" << "0" << localtimeB << "\n" << endl;}
      else{
        dataFile << "" << "Localtime: " << localtimeA << ":" << localtimeB << "\n" << endl;}  
     dataFile << "" << "Sensor1 Humidity: " << humidity << " %\t " << "Temperature: " << temp_c << " *C\n" << endl; 
     dataFile << "" << "Sensor2 Humidity: " << humidity2 << " %\t " << "Temperature: " << temp_c2 << " *C\n" << endl; 
     dataFile << "" << "Sensor3 Humidity: " << humidity3 << " %\t " << "Temperature: " << temp_c3 << " *C\n" << endl;       
     dataFile.close();
  }  
  // Als de SD niet bereikbaar is, geef een error via serial en in de errorlog:
  else {
    Serial.println("error opening SD");
  } 
  

// LOGDATA VIA FTP VERZENDEN
//--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\\

//Gegevens over FTP naar FTP server verzenden
  //FTP 
  if(sentFile(fileName)){
    Serial.println("FTP OK");
  }
  else{
    Serial.println("FTP FAIL");
    File errorfile = SD.open("errorlog.txt", FILE_WRITE);
    if (errorfile) {
      errorfile << "local time: " << year() << "/" << month() << "/" << day() << "" << endl; 
      if (localtimeB < 10 ) {
        dataFile << "" << "Localtime: " << localtimeA << ":" << "0" << localtimeB << "Failed sending data over FTP\n" << endl;}  
      else{
        dataFile << "" << "Localtime: " << localtimeA << ":" << localtimeB << "Failed sending data over FTP\n" << endl;}  
      errorfile.close();
      }
  }
 }
}