Read Data from SD with Arduino (MicroSD module and Ethernet Shield)

In this new post I will show you a simple Arduino code to read data from a txt file that is on an SD card.

Leer archivo de SD

To do this I have used the same modules than in the previous post: Write data to an SD card with Arduino.

The connections will also be the same:

· For the ethernet module is only necessary to fit it correctly on the Arduino board and connect the potentiometer to the analog Pin 0.

· In the case of the MICRO SD CARD Adapter module is required to make the following connections:

- MOSI –> Pin 11 (Most Arduino boards), for Arduino Mega: 51
– MISO –> Pin 12 (Most Arduino boards), for Arduino Mega: 50
– CLK —-> Pin 13 (Most Arduino boards), for Arduino Mega: 52
– CS ——> Pin 4
– 5V ——> 5V
– GND –> GND

More information in

The following code reads and sends via serial port the content of a file called “readme.txt” (We have to create it with the computer in the SD card):

// Read Data from SD with Arduino

//We include the SD library.
#include <SD.h>
// We store in what Arduino input the pin CS of the module is connected.
const int chipSelect = 4;

void setup(){
  // We set up the serial port to send error messages through It.
  // The default CS pin of the Arduino board must be configured as an output
  // even when not used (10 in most of the boards, 53 in Arduino Mega).
  pinMode(10, OUTPUT);
  // If there has been an error reading the SD card we send a message through the serial port.
  if (!SD.begin(chipSelect)){
    Serial.println("Error reading the SD card.");

  //We write the program inside the setup to only run it once.

  // We open the file.
  File dataFile ="readme.txt");
  // If the file is correct:
  if (dataFile) {
    // We show a message saying that the content of the txt file starts below.
    Serial.println("* The content of readme.txt is shown below:");
    // We read the file and send the data through the serial port.
    while (dataFile.available()) {
    // We close the file.
  // If we could not open the file we send an error message through the serial port.
  }else {
    Serial.println("Error opening readme.txt");

//We Don't write anything in the loop.
void loop()

Sources: Arduino SD Library