Tutorials > Examples from Libraries > SD > DumpFile

Using the SD library to retrieve information over a serial port

This example shows how to read a file from a SD card using the SD library and send it over the serial port. Please click here for more information on the SD library.

Hardware Required

  • Arduino or Genuino board
  • Ethernet Shield (or other board with an SD slot)
  • Formatted SD card with a file named "datalog.txt" containing some text

Circuit

image developed using Fritzing. For more circuit examples, see the Fritzing project page

The Arduino or Genuino board has to be connected to the Ethernet Shield and also has a USB cable connected to the computer.

Schematics

image developed using Fritzing. For more circuit examples, see the Fritzing project page

Code

The code below is configured for use with an Ethernet shield, which has an onboard SD slot. In the setup(), call SD.begin(), naming pin 4 as the CS pin. This pin varies depending on the make of shield or board you are using.

On the SD card, there is a file named "datalog.txt". In the loop(), the file is opened when calling SD.open(). To send the file serially to a computer, use Serial.print(), reading the contents of the file with SD.read().

/*
  SD card file dump

 This example shows how to read a file from the SD card using the
 SD library and send it over the serial port.

 The circuit:
 * SD card attached to SPI bus as follows:
 ** MOSI - pin 11
 ** MISO - pin 12
 ** CLK - pin 13
 ** CS - pin 4 (for MKRZero SD: SDCARD_SS_PIN)

 created  22 December 2010
 by Limor Fried
 modified 9 Apr 2012
 by Tom Igoe

 This example code is in the public domain.

 */

#include <SPI.h>
#include <SD.h>

const int chipSelect = 4;

void setup() {
  // Open serial communications and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }


  Serial.print("Initializing SD card...");

  // see if the card is present and can be initialized:
  if (!SD.begin(chipSelect)) {
    Serial.println("Card failed, or not present");
    // don't do anything more:
    while (1);
  }
  Serial.println("card initialized.");

  // open the file. note that only one file can be open at a time,
  // so you have to close this one before opening another.
  File dataFile = SD.open("datalog.txt");

  // if the file is available, write to it:
  if (dataFile) {
    while (dataFile.available()) {
      Serial.write(dataFile.read());
    }
    dataFile.close();
  }
  // if the file isn't open, pop up an error:
  else {
    Serial.println("error opening datalog.txt");
  }
}

void loop() {
}
[Get Code]

See Also


  • CardInfo - Get info about your SD card.
  • Datalogger - How to log data from three analog sensors to an SD card.
  • Files - How to create and destroy an SD card file.
  • Listfiles - How print out the files in a directory on a SD card.
  • ReadWrite - How to read and write data to and from an SD card.


Last revision 2015/08/18 by SM