Using the SD library to read and write to a file on a SD card

This example shows how to read and write data to and from an SD card. Please click here for more information on the SD library.

Hardware Required

Arduino board
Ethernet Shield (or other board with an SD slot)
Formatted SD card

Circuit

EthernetShield Fritz

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

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

Schematics

Ethernet Shield Sch

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(), we call SD.begin(), naming pin 4 as the CS pin. This pin varies depending on the make of shield or board you are using.

In setup(), create a new file with SD.open() named "test.txt". FILE_WRITE enables read and write access to the file, starting at the end. If a file "test.txt" was already on the card, that file would be opened.

Name the instance of the opened file "myFile".

Once opened, use myFile.println() to write a string to the card, followed by a carriage return. Once the content is written, close the file.

Again, open the file with SD.open(). Once opened, ask the Arduino to read the contents of the file with SD.read() and send them over the serial port. After all the contents of the file are read, close the file with SD.close().

Table of Contents

Using the SD library to read and write to a file on a SD card

Hardware Required

Circuit

Schematics

Code

See Also