SENSORS/ACTUATORS

INTERNET OF THING (IoT)

ESP32 - SD Card

In this guide, we'll explore how to use a Micro SD Card with the ESP32. We'll delve into the following topics:

How to open a file on the Micro SD Card using the ESP32, and also how to create a new one if it doesn't already exist.
How to write data to a file on the Micro SD Card using the ESP32.
How to read a file on the Micro SD Card character by character using the ESP32.
How to read a file on the Micro SD Card line by line using the ESP32.
How to add more content to an existing file on the Micro SD Card using the ESP32.
How to replace the content of a file on the Micro SD Card using the ESP32.

Hardware Used In This Tutorial

1	×	ESP-WROOM-32 Dev Module
1	×	USB Cable Type-C
1	×	Micro SD Card
1	×	Micro SD Card Module
1	×	Jumper Wires
1	×	Breadboard
1	×	(Optional) MicroSD to SD Memory Card Adapter
1	×	(Recommended) Screw Terminal Expansion Board for ESP32
1	×	(Recommended) Power Splitter For ESP32

Or you can buy the following sensor kits:

1	×	DIYables Sensor Kit (30 sensors/displays)
1	×	DIYables Sensor Kit (18 sensors/displays)

Disclosure: Some of the links in this section are Amazon affiliate links, meaning we may earn a commission at no additional cost to you if you make a purchase through them. Additionally, some links direct you to products from our own brand, DIYables.

Introduction to Micro SD Card Module

The Micro SD Card Module can interface with ESP32 and it can carry a Micro SD Card. In another word, the Micro SD Card Module is a bridge between ESP32 and Micro SD Card

Pinout

Micro SD Card Module includes 6 pins:

VCC pin: connect to the ESP32's 5V pin.
GND pin: connect this pin to the ESP32's GND.
MISO pin: (Master In Slave Out) connect this pin to the ESP32's MISO pin.
MOSI pin: (Master Out Slave In) connect this pin to the ESP32's MOSI pin.
SCK pin: connect this pin to the ESP32's SCK pin.
SS pin: (Slave Select) connect this pin to the pin specified in ESP32 code as a SS pin.

Preparation

Connect the Micro SD Card to the PC via USB 3.0 SD Card Reader
Make sure that the Micro SD Card is formatted FAT16 or FAT32 (Google for it)

Wiring Diagram

This image is created using Fritzing. Click to enlarge image

※ NOTE THAT:

If you use an Ethernet shield or any shield that has a Micro SD Card Holder, you do not need to use the Micro SD Card Module. You just need to insert the Micro SD Card to the Micro SD Card Holder on the shield.

If you're unfamiliar with how to supply power to the ESP32 and other components, you can find guidance in the following tutorial: How to Power ESP32.

ESP32 - How to open a file on Micro SD Card and create if not existed

ESP32 Code

Quick Instructions

If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE.
Open Arduino IDE on your PC.
Select the right ESP32 board (e.g. ESP32 Dev Module) and COM port.
Insert the Micro SD Card to the Micro SD Card module
Do the wiring between the Micro SD Card module and ESP32 as the above wiring diagram
Connect ESP32 to PC via USB cable
Open Arduino IDE, select the right board and port
Open Serial On Arduino IDE
Copy the above code and paste it to Arduino IDE
Click Upload button on Arduino IDE to upload code to ESP32
The result on Serial Monitor for the first run

COM6

Send

SD CARD INITIALIZED. esp32.txt doesn't exist. Creating esp32.txt file... esp32.txt exists on SD Card.

Autoscroll Show timestamp

Clear output

9600 baud

Newline

The result on Serial Monitor for the next runs

COM6

Send

SD CARD INITIALIZED. esp32.txt exists on SD Card.

Autoscroll Show timestamp

Clear output

9600 baud

Newline

※ NOTE THAT:

You may NOT see the output on Serial Monitor for the first run of your first upload is done before opening Serial Monitor.

Detach the Micro SD Card from the module
Insert the Micro SD Card to an USB SD Card reader
Connect the USB SD Card reader to the PC
Check if the file exists or not

ESP32 - How to write/read data to/from a file on Micro SD Card

The below code does:

Write data to a file
Read the content of the a file character-by-character and print it to Serial Monitor

/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-sd-card */ #include <SD.h> #define PIN_SPI_CS 5 // The ESP32 pin GPIO5 File myFile; void setup() { Serial.begin(9600); if (!SD.begin(PIN_SPI_CS)) { while (1) { Serial.println(F("SD CARD FAILED, OR NOT PRESENT!")); delay(1000); } } Serial.println(F("SD CARD INITIALIZED.")); // open file for writing myFile = SD.open("/esp32.txt", FILE_WRITE); if (myFile) { myFile.println("Created by esp32io.com"); // write a line to esp32.txt myFile.println("Learn ESP32 and SD Card"); // write another line to esp32.txt myFile.close(); } else { Serial.print(F("SD Card: Issue encountered while attempting to open the file esp32.txt")); } // open file for reading myFile = SD.open("/esp32.txt", FILE_READ); if (myFile) { while (myFile.available()) { char ch = myFile.read(); // read characters one by one from Micro SD Card Serial.print(ch); // print the character to Serial Monitor } myFile.close(); } else { Serial.print(F("SD Card: Issue encountered while attempting to open the file esp32.txt")); } } void loop() { }

The Serial Monitor shown the content of the file

COM6

Send

Created by esp32io.com Learn ESP32 and SD Card

Autoscroll Show timestamp

Clear output

9600 baud

Newline

※ NOTE THAT:

The data will be appended to the end of file by default. If you reboot ESP32 with above code, the text will be appended to the file again ⇒ the Serial Monitor will shows more lines as below:

COM6

Send

Created by esp32io.com Learn ESP32 and SD Card Created by esp32io.com Learn ESP32 and SD Card

Autoscroll Show timestamp

Clear output

9600 baud

Newline

You can also detach the Micro SD Card from the module, and open it on your PC to check the content (USB SD Card reader is needed)

ESP32 - How to read a file on Micro SD Card line-by-line

/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-sd-card */ #include <SD.h> #define PIN_SPI_CS 5 // The ESP32 pin GPIO5 File myFile; void setup() { Serial.begin(9600); if (!SD.begin(PIN_SPI_CS)) { while (1) { Serial.println(F("SD CARD FAILED, OR NOT PRESENT!")); delay(1000); } } Serial.println(F("SD CARD INITIALIZED.")); // open file for writing myFile = SD.open("/esp32.txt", FILE_WRITE); if (myFile) { myFile.println("Created by esp32io.com"); // write a line to esp32.txt myFile.println("Learn ESP32 and SD Card"); // write another line to esp32.txt myFile.close(); } else { Serial.print(F("SD Card: Issue encountered while attempting to open the file esp32.txt")); } // open file for reading myFile = SD.open("/esp32.txt", FILE_READ); if (myFile) { int line_count = 0; while (myFile.available()) { char line[100]; // maximum is 100 characters, change it if needed int line_length = myFile.readBytesUntil('\n', line, 100); // read line-by-line from Micro SD Card line_count++; Serial.print(F("Line ")); Serial.print(line_count); Serial.print(F(": ")); Serial.write(line, line_length); // print the character to Serial Monitor // \n character is escaped by readBytesUntil function Serial.write('\n'); // print a new line charactor } myFile.close(); } else { Serial.print(F("SD Card: Issue encountered while attempting to open the file esp32.txt")); } } void loop() { }

The result on Serial Monitor

COM6

Send

SD CARD INITIALIZED. Line 1: Created by esp32io.com Line 2: Learn ESP32 and SD Card

Autoscroll Show timestamp

Clear output

9600 baud

Newline

※ NOTE THAT:

You may see more lines on Serial Monitor if the content of the file is not deleted before.

ESP32 - How to overwrite a file on Micro SD Card

By default, the content will append to the end of the file. The simplest way to overwrite a file is: delete the exsiting file and create new one with the same name

/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-sd-card */ #include <SD.h> #define PIN_SPI_CS 5 // The ESP32 pin GPIO5 File myFile; void setup() { Serial.begin(9600); if (!SD.begin(PIN_SPI_CS)) { while (1) { Serial.println(F("SD CARD FAILED, OR NOT PRESENT!")); delay(1000); } } Serial.println(F("SD CARD INITIALIZED.")); SD.remove("/esp32.txt"); // delete the file if existed // create new file by opening file for writing myFile = SD.open("/esp32.txt", FILE_WRITE); if (myFile) { myFile.println("Created by esp32io.com"); // write a line to esp32.txt myFile.println("Learn ESP32 and SD Card"); // write another line to esp32.txt myFile.close(); } else { Serial.print(F("SD Card: Issue encountered while attempting to open the file esp32.txt")); } // open file for reading myFile = SD.open("/esp32.txt", FILE_READ); if (myFile) { while (myFile.available()) { char ch = myFile.read(); // read characters one by one from Micro SD Card Serial.print(ch); // print the character to Serial Monitor } myFile.close(); } else { Serial.print(F("SD Card: Issue encountered while attempting to open the file esp32.txt")); } } void loop() { }

The result on Serial Monitor

COM6

Send

SD CARD INITIALIZED. Created by esp32io.com Learn ESP32 and SD Card

Autoscroll Show timestamp

Clear output

9600 baud

Newline

Reboot ESP32
Check if the content of the file on Serial Monitor is appended or not.

You can also detach the Micro SD Card from the module, and open it on your PC to check the content (USB SD Card reader is needed)

Video Tutorial

Making video is a time-consuming work. If the video tutorial is necessary for your learning, please let us know by subscribing to our YouTube channel , If the demand for video is high, we will make the video tutorial.

Function References

Learn More

※ OUR MESSAGES

As freelancers, We are AVAILABLE for HIRE. See how to outsource your project to us
If this tutorial is useful for you, please support us to make more tutorials.
Please feel free to share the link of this tutorial. However, Please do not use our content on any other websites. We invested a lot of effort and time to create the content, please respect our work!