Title data while saving on SD card

[iqbalwijaya]

Hi, I'm working on my sensor, and I'm trying to save data to the sd card. I need the header/title data only in the first row of the stored data, how can I write the code, and where should it be placed? because if it is placed in a loop then it will appear continuously.

this is the code I made to read my sensor.

#include <SD.h>
#include <SPI.h>
#include <DS3231.h>
#define MQ2pin (A0)

float sensorValue;  //variable to store sensor value


File myFile;
DS3231  rtc(SDA, SCL);

int pinCS = 10; // Pin 10 on Arduino Uno

void setup() {
    
  Serial.begin(9600);
  pinMode(pinCS, OUTPUT);
  
  // SD Card Initialization
  if (SD.begin())
  {
    Serial.println("Gas sensor warming up!");
    delay(2000); // allow the MQ-6 to warm up
    Serial.println("SD card is ready to use.");
    Serial.println("Time, sensor Value");
  } else
  {
    Serial.println("SD card initialization failed");
    return;
  
  }
  rtc.begin();    
}
void loop() {
  sensorValue = analogRead(MQ2pin); // read analog input pin 0
  Serial.print(rtc.getDateStr()); //prosedur pembacaan tanggal
  Serial.print(",");
  Serial.print(rtc.getTimeStr()); //prosedur pembacaan waktu
  Serial.print(",");
  Serial.print(sensorValue);
  Serial.println(" ");

myFile = SD.open("File1.txt", FILE_WRITE);
  if (myFile) {  
    myFile.print(rtc.getDateStr());
    myFile.print(",");
    myFile.print(rtc.getTimeStr());
    myFile.print(",");
    myFile.print(sensorValue);  
    myFile.println(" ");
    
    
    myFile.close(); // close the file
  }
  // if the file didn't open, print an error:
  else {
    Serial.println("error opening test.txt");
  }

and this is the output

result that i want

[Idahowalker]

write the header in setup().

Better yet use a text editor make your text file headers, save it to the SD card, and use file.append() to add to the data text.

[michael_x]

Check if file exists, if not, create and add header line, else open in append mode, like @Idahowalker suggested.