Back to Arduino Step By Step Course

Lesson 106: Using Micro SD Card and Data logging with Arduino

If you don't like to see ads while video is being played you can purchase this course for $200 from Udemy or purchase YouTube premium Here

Please select other codes for this lecture from the links below.

  • Purchase Micro SD Card module from Amazon USA
  • Purchase Micro SD Card module from Amazon Canada
  • Purchase Micro SD Card module from all other Amazon
  • Purchase Micro SD Card module from AliExpress
  • Purchase Micro SD Card module from Banggood
  • Part 23: Data Storage

    In this lesson we learn how to do use Micro SD card. We learn how to write to the card, how to read text. How to log voltage from potentiometer to memory card. How to save the data as csv format so we can open it on Spreadsheet like Excel for plotting and other analysis.

    This is Example 5 We simply read the voltage frompotentiometer and when push button is pressed the data from Micro SD card is displayed on serial monitor. The data written in microSD card is written in CSV format so we can open it using spreasheet like Excel.


     Original from File->Examples->SD  SD card read/write
      * Lesson 106-1: Reading voltage from potentiometer and saving it on microSD card
      In this example we red A0 pin to read potentionmeter's voltage
     and writing it to the Micro SD card.
     We have also push button, when pressed, it will print the 
     file data on the serial monitor.
     In the lesson
     Example 1: Card info demonstrated
     Example 2: file list demonstrated
     Example 3: Datalogger
     Example 4: DoNotBlockWrite
     Example 5 (this code): Reading potentionmter saving on micro SD card and using push button to read it
     Example 6: Using example 5 but creating CSV file so we open it on Excel
     Example 7: Writing into two files at the ame time in micro SD Card
      * Watch Video instrution for this code:
      * This code is part of Arduino Step by Step Course which starts here:
      * for library of this code visit
     If you found this tutorial helpful, please support me so I can continue creating 
     content like this. Make a donation using PayPal by credit card 
     written/udpated by Ahmad Shamshiri on Jun 18, 2022
      *  * This code is "AS IS" without warranty or liability. Free to be used as long as you keep this note intact.* 
      * This code has been download from
         This program is free software: you can redistribute it and/or modify
         it under the terms of the GNU General Public License as published by
         the Free Software Foundation, either version 3 of the License, or
         (at your option) any later version.
         This program is distributed in the hope that it will be useful,
         but WITHOUT ANY WARRANTY; without even the implied warranty of
         GNU General Public License for more details.
         You should have received a copy of the GNU General Public License
         along with this program.  If not, see <>.
        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   Nov 2010
       by David A. Mellis
       modified 9 Apr 2012
       by Tom Igoe
       This example code is in the public domain.
     #include <SPI.h>
     #include <SD.h>
     //serial monitor print while writing log
     boolean serialPrint = true;//true or false
     char *logFile ="datalog.txt";//file name. must be max 8 character excluding the extension (book.txt is 4 char)
     int readPushButtonPin = 9;
     File myFile;
     void writLog(float);//prototype of writLog funciton at the bottom of this code
     void readLog(void);//prototype of readLog funciton at the bottom of this code
     void setup() {
       //Watch the instruction to this code on youTube
       // Open serial communications and wait for port to open:
       while (!Serial) {
         ; // wait for serial port to connect. Needed for native USB port only
       pinMode(readPushButtonPin, INPUT_PULLUP);
       Serial.print("Initializing SD card...");
       if (!SD.begin(4)) {
         Serial.println("initialization failed!");
         while (1);
       Serial.println("initialization done.");
       // open the file. note that only one file can be open at a time,
       // so you have to close this one before opening another.
         myFile =, FILE_WRITE);
        if (!myFile) {
         Serial.println("log file missing");
     void loop() {
       int sensor = analogRead(A0);//read A0 pin
       //convert value of 0 to 1023 to voltage. 
       //Arduino UNO is 5V so we use 5
       float voltage = sensor * (5.0 / 1023.0);
       if(digitalRead(readPushButtonPin) == LOW)
          //Watch the instruction to this code on youTube
     void writLog(float voltage)
        myFile =, FILE_WRITE);
       //Watch the instruction to this code on youTube
         myFile.print("Time: ");//writing the text: Time:
         myFile.print(millis()/1000); //recod time  
         myFile.print("	Voltage: ");//writing the text Volage after a tab 	
         myFile.print(voltage);//Writing voltage
         myFile.println("V");//adding V at the end
           Serial.print ("Time:");
           Serial.print ("	Voltage: ");
         // close the file:
           Serial.println(" done.");
      * readLog
      * Reads the datas from MicroSD Card and prints it on serial monitor
     void readLog()
       //Watch the instruction to this code on youTube
       // re-open the file for reading:
       myFile =;
       if (myFile) {
         Serial.print("Reading ========");
         // read from the file until there's nothing else in it:
         while (myFile.available()) {
         Serial.print("Reading END==========");
         // close the file:
       } else {
         // if the file didn't open, print an error:
         Serial.print("readLog() error opening ");
         //Watch the instruction to this code on youTube

    The least I expect from you is to thumb up the video and subscribe to my channel. I appriciate that. .I have spent months making these lectures and writing code. You don't lose anything by subscribging to my channel. Your subscription is stamp of approval to my videos and more people can find them and in it turn it helps me. Thank you

    If you found this tutorial helpful, please support me so I can continue creating content like this. support me via PayPal

    **** AFFILIATE PROGRAM **** We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to and affiliated sites.