Data Logger

Make sure you have installed the Arduino IDE on your computer. You can download it from Arduino directly (external link).
Make sure you have selected the correct board and port of your connected Arduino. If needed use the board manager under "Tools" to search for missing ones.
It is always a good idea to comment your code while writing it. If you might switch boards down the track it is also a good idea to use "#define" for defining your used pins. This way you don't have to search for those pins later in your code if you would like to change them.

The below code example just shows how to switch the relais on and off while also writing to the SD card.

#include <SPI.h>
#include <SdFat.h>

#define chipSelect SDCARD_SS_PIN
#define RELAY1 1
#define RELAY2 2

SdFat32 sd;
File32 file;
#define dataLog "datalog.txt"

void InitializeSD() {
    Serial.print("Initializing SD card...");
    // see if the card is present and can be initialized:
    if (!sd.begin(chipSelect)) {
        //sd.initErrorHalt(&Serial);        
        Serial.println("Card failed, or not present");
        // don't do anything more:
    }
    Serial.println("card initialized.");
}

void WriteToSD(String _fileName,String _dataString) {
    file = sd.open(_fileName, FILE_WRITE);
    // if the file is available, write to it:
    if (file) {
        file.println(_dataString);
        file.close();
    }
    // if the file isn't open, pop up an error:
    else {
        Serial.println("error opening datalog.txt");
    }
}


void setup() {
    Serial.begin(9600);
    InitializeSD();
    pinMode(RELAY1, OUTPUT);
    pinMode(RELAY2, OUTPUT);
    digitalWrite(RELAY1,LOW);
    digitalWrite(RELAY2,HIGH);
}

void loop() {
  Serial.println("Switch Relais 1");
  digitalWrite(RELAY1,!digitalRead(RELAY1)); //reads the state of relais 1 and inverts it
  WriteToSD(dataLog,"Switch Relais 1");
  delay(2000);
  Serial.println("Switch Relais 2");
  digitalWrite(RELAY2,!digitalRead(RELAY2)); //reads the state of relais 1 and inverts it
  WriteToSD(dataLog,"Switch Relais 2");
  delay(2000);
}