First off. This is not in any way a class assignment. This is my own personal work and research. I just want to get that out of the way.

I am learning how to use Matlab with various Arduino projects. I am a seasoned Matlab user but I am fairly new to the entire Arduino space.

I am trying to send some numerical data from Matlab (via a GUI) to my Arduino Uno and have the Arduino write it to my micro SC card. This is a temporary step to my larger project. However, there is no need to go into those specifics as they are outside of the scope of my issues.

I am fairly confident that the Matlab code works and the Arduino code is slightly modified from another project I did where I wrote and read random numbers from my micro SD card.

However, as I run the Matlab code, the Arduino blinks as if it is receiving the data but after I check the micro SD card it remains blank.

I am confident that my Arduino is wired correctly to my micro SD card adapter since this remains the same from my prior project.

Therefore, I am sure I am missing something trivial to get it to work.

I have researched several websites on the subject and their method and mine seem to align very well.

I am fairly certain the problem is in the conditional statement:

if (Serial.available() > 0) {

As you will see.

The Matlab code is below:

arduinoCom = serial('COM3', 'BaudRate', 115200);  
sendData = 5;
fprintf(arduinoCom,'%i',sendData); %this will send 5 to the arduino

The Arduino code is as follows:

#include <SD.h> // load SD library

int chipSelect = 4;  // Chip select pin for the MicroSD Card Adapter
int incomingByte = 0; // for incoming serial data.
File SDF; // Serial data received is saved here.

void setup() {
     Serial.begin(115200); // start serial connection to print out debug messages and data
     pinMode(chipSelect, OUTPUT); // chip select pin must be set to OUTPUT mode
     if (!SD.begin(chipSelect)) { // Initialize SD card
        Serial.println("Could not initialize SD card."); // if return value is false, something went wrong.
     while (!Serial) {

void loop() {
        // Open file, Write data, Close file only when you receive data
        if (Serial.available() > 0) {
           incomingByte = Serial.read();
           SDF = SD.open("SerialDataFile.txt", FILE_WRITE); // open "SerialDataFile.txt" to write data
           SDF.println(incomingByte, DEC); // write ASCII-encoded decimal number to file
           SDF.close(); // close file

The expected result would be a file "SerialDataFile.txt" stored on my micro SD card with the value 5.

Thank you for your help!

  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Nick Gammon
    Jan 24, 2019 at 6:09
  • Look, this is not a forum. Please refrain from answering the question, or making suggestions, in comments. Comments under the question are for clarifying any confusing parts of the question, and requesting further information.
    – Nick Gammon
    Jan 24, 2019 at 6:10
  • I am not seeing a way to check this answer as complete. - there is some sort of time delay. Check back tomorrow.
    – Nick Gammon
    Jan 24, 2019 at 6:12

1 Answer 1


The board resets on new USB connection with fopen. Wait 2 secs between fopen and fprintf in Mathlab code.


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