Using the SD library to log data

This example shows how to use the SD card Library to log data from three analog sensors to a SD card. 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)
3 x 10k Ohm Potentiometers
1 x Mini Breadboard 

1 x USB Type-B Cable 

1 x Formatted SD card
Male-to-Male Jumper Wires 

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. The three potentiometers may be substituted with other analog sensors, to be wired according to their interfacing techniques.

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 >> Datalogger

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

/*
SD card datalogger This example shows how to log data from three analog sensors
to an SD card using the SD library. The circuit:
* analog sensors on analog ins 0, 1, and 2
* SD card attached to SPI bus as follows:
** MOSI - pin 11
** MISO - pin 12
** CLK - pin 13
** CS - pin 4 created 24 Nov 2010
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.");
} void loop() {
// make a string for assembling the data to log:
String dataString = ""; // read three sensors and append to the string:
for (int analogPin = 0; analogPin < 3; analogPin++) {
int sensor = analogRead(analogPin);
dataString += String(sensor);
if (analogPin < 2) {
dataString += ",";
}
} // 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", FILE_WRITE); // if the file is available, write to it:
if (dataFile) {
dataFile.println(dataString);
dataFile.close();
// print to the serial port too:
Serial.println(dataString);
}
// if the file isn't open, pop up an error:
else {
Serial.println("error opening datalog.txt");
}
}

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.

In the loop(), a String is created to hold the information from three analog sensors. The code iterates through the sensors, adding their data to the string.

Next, the file on the SD card is opened by calling SD.open(). Once available, the data is written to the card when dataFile.println() is used. The file must be closed with dataFile.close() to save the information.

Download:

Arduino IDE

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

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