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.

Step 1: What You Need?

1 x Arduino Board ( Arduino UNO used in this tutorial) 
1 x Arduino Ethernet Shield (or other board with an SD slot)
1 x Formatted SD card with a file named "datalog.txt" containing some text

1 x USB Type-B Cable 

Don't have components? Don't worry. Just click the component's name. 

Step 2: Build Your Circuit.

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

Step 3: Upload The Code.

1. Select the Arduino board type: Select Tools >> Board >> Select your correct Arduino board used.

2. Find the port number by accessing device manager on Windows. See the section Port (COM&LPT) and look for an open port named "Arduino Uno (COMxx)". If you are using a different board, you will find a name accordingly. What matters is the xx in COMxx part. In my case, it's COM3. So my port number is 3.

Select the right port: Tools >> Port >> Select the port number.

3. You can find this code in the example of Arduino IDE.

Select File >> Examples >> SD >> DumpFile

Click press the "upload" button (see the button with right arrow mark).

/*
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 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:
return;
}
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() {
}

The code above 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().

Download:

Arduino IDE

Sources:https://www.arduino.cc/en/Tutorial/DumpFile   

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