i want to save a vector to a .csv file on a SD Card.

I watched this tutorial on how to do it and it describes it perfectly even though its kinda dated.

My Problem is that everything is saved into the first cell of the .csv file so it gets constantly overridden. It should save only the first vector into the first cell, then the second vector into the second cell and so on. I just get all three vectors with the commas into the first vector like this:

8, 9, 10

Also the header witch should appear at the top is also gone.

I would really appreciate some help. Thanks!

Here is my setup and loop:

#include <iostream>
#include <string>
#include <vector>
#include "SD.h"
#include "SPI.h"
#include "EKG_data_transmision.h"

#define CS_Pin 5 // Chip Select Pin

EKG_data_transmision EKG_data_transmision;

std::vector<unsigned short> vector_1 = {1,2,3,4,5,6,7,8,9,10};
std::vector<unsigned short> vector_2 = {2,3,4,5,6,7,8,9,10,11};
std::vector<unsigned short> vector_3 = {3,4,5,6,7,8,9,10,11,12};
unsigned int for_x = 0;

void setup() {
  // open serial
  Serial.print("Init SD Card...");
  pinMode(CS_Pin, OUTPUT);

    Serial.println("Card failed or not present");

  EKG_data_transmision.vectorData = SD.open("/data.csv", FILE_WRITE);  //erstelle data.csv datei

    EKG_data_transmision.vectorData.println(", , , ,");
    String header = "ID, Value, Time, Whatever";
    Serial.println("card init sucess");
    Serial.println("Couldnt open vector data file");


void loop() {
  // put your main code here, to run repeatedly:

  while(for_x <= 8){
    EKG_data_transmision.write_vector_to_SD(vector_1, vector_2, vector_3);


Here is my function that should save everything to the SD Card:

bool  EKG_data_transmision::write_vector_to_SD(std::vector<unsigned short> vector_ADC_1, std::vector<unsigned short> vector_ADC_2, std::vector<unsigned short> vector_ADC_3) // Übertrage
  dataString = String(vector_loc) + "," + String(vector_ADC_1[vector_loc]) + "," + String(vector_ADC_2[vector_loc]) + "," + String(vector_ADC_3[vector_loc]); // + "\r\n"

  vectorData = SD.open("/data.csv", FILE_WRITE);

    //sd karte immer noch da und schau ob data.csv exisitiert
    Serial.println("This is vector:");
    Serial.println("Im actually writing this:");
    vectorData.close(); // close the file

    Serial.println("Error writing to file !");

  return 0;
  • Thanks for your fast answer. I just changed every WRITE to APPEND. Now the values get saved into different cells but only into Row A. I thought with "," it switches into different rows. Do you have an answer to that? – Xenoshell Nov 24 '19 at 15:41
  • in my language Excel uses ; for csv, because we have , as decimal separator – Juraj Nov 24 '19 at 15:54
  • Thanks a lot for you help!! I just tried it and with ; it works perfectly. – Xenoshell Nov 24 '19 at 16:08
  • I moved the first comment to an answer – Juraj Nov 25 '19 at 20:22

In Arduino SD library FILE_WRITE constant instructs the function to open the file for append, but in the esp32 SD library it opens the file for rewrite. Use FILE_APPEND to open the file for append.

File file = SD.open(path, FILE_APPEND); 
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