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ESP32 - Write Variable to SD Card
In this tutorial, we'll explore the process of writing various types of variables to a Micro SD Card using ESP32. Specifically, we'll cover the following topics:
- Writing a string variable to a Micro SD Card with ESP32.
- Writing an integer variable to a Micro SD Card with ESP32.
- Writing a float variable to a Micro SD Card with ESP32.
- Writing a character array variable to a Micro SD Card with ESP32.
- Writing a byte array variable to a Micro SD Card with ESP32.
- Writing a variable as a key-value pair to a Micro SD Card with ESP32.
This tutorial provides a comprehensive guide for storing different types of variables on a Micro SD Card, allowing for versatile data storage and retrieval. To learn how to read key-value pairs from the Micro SD Card and convert them to integer, float, and string formats, refer to the tutorial on ESP32 - Read Config from SD Card.
Hardware Used In This Tutorial
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
Unfamiliar with Micro SD Card Module, including their pinouts, functionality, and programming? learn about them in the ESP32 - Micro SD Card tutorial.
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 write a variable to a file on Micro SD Card
The below code does:
- Write a int variable to Micro SD Card
- Write a float variable to Micro SD Card
- Write a string variable to Micro SD Card
- Write a char array to Micro SD Card
- Write a byte array to Micro SD Card
/*
* 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-write-variable-to-sd-card
*/
#include <SD.h>
#define PIN_SPI_CS 5 // The ESP32 pin GPIO5
File myFile;
int myInt = -52;
float myFloat = -12.7;
String myString = "HELLO";
char myCharArray[] = "esp32io.com";
byte myByteArray[] = {'1', '2', '3', '4', '5'};
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."));
Serial.println(F("--------------------"));
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(myInt); // write int variable to SD card in line
myFile.println(myFloat); // write float variable to SD card in line
myFile.println(myString); // write String variable to SD card in line
myFile.println(myCharArray); // write char array to SD card in line
myFile.write(myByteArray, 5);
myFile.write("\n"); // new line
for (int i = 0; i < 5; i++) {
myFile.write(myByteArray[i]); // new line
if (i < 4)
myFile.write(","); // comma
}
myFile.write("\n"); // new line
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() {
}
Quick Instructions
- If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE.
- Do the wiring as above image.
- Connect the ESP32 board to your PC via a micro USB cable
- Open Arduino IDE on your PC.
- Select the right ESP32 board (e.g. ESP32 Dev Module) and COM port.
- Make sure that the Micro SD Card is formatted FAT16 or FAT32 (Google for it)
- Copy the above code and open with Arduino IDE
- Click Upload button on Arduino IDE to upload code to ESP32
- See the result on Serial Monitor.
COM6
SD CARD INITIALIZED.
--------------------
-52
-12.70
HELLO
esp32io.com
12345
1,2,3,4,5
Autoscroll
Clear output
9600 baud
Newline
- Detach the Micro SD Card from the Micro SD Card module
- Insert the Micro SD Card to an USB SD Card reader
- Connect the USB SD Card reader to the PC
- Open the esp32.txt file on your PC, it looks like below
ESP32 - How to write a key-value to a file on Micro SD Card
/*
* 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-write-variable-to-sd-card
*/
#include <SD.h>
#define PIN_SPI_CS 5 // The ESP32 pin GPIO5
File myFile;
int myInt = -52;
float myFloat = -12.7;
String myString = "HELLO";
char myCharArray[] = "esp32io.com";
byte myByteArray[] = {'1', '2', '3', '4', '5'};
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."));
Serial.println(F("--------------------"));
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.print("myInt="); // write key to SD card
myFile.println(myInt); // write int variable to SD card in line
myFile.print("myFloat="); // write key to SD card
myFile.println(myFloat); // write float variable to SD card in line
myFile.print("myString="); // write key to SD card
myFile.println(myString); // write String variable to SD card in line
myFile.print("myCharArray="); // write key to SD card
myFile.println(myCharArray); // write char array to SD card in line
myFile.print("myByteArray="); // write key to SD card
myFile.write(myByteArray, 5);
myFile.write("\n"); // new line
myFile.print("myByteArray2="); // write key to SD card
for (int i = 0; i < 5; i++) {
myFile.write(myByteArray[i]); // new line
if (i < 4)
myFile.write(","); // comma
}
myFile.write("\n"); // new line
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() {
}
Quick Instructions
- If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE.
- Do the wiring as above image.
- Connect the ESP32 board to your PC via a micro USB cable
- Open Arduino IDE on your PC.
- Select the right ESP32 board (e.g. ESP32 Dev Module) and COM port.
- Copy the above code and open with Arduino IDE
- Click Upload button on Arduino IDE to upload code to ESP32
- See the result on Serial Monitor.
COM6
SD CARD INITIALIZED.
--------------------
myInt=-52
myFloat=-12.70
myString=HELLO
myCharArray=esp32io.com
myByteArray=12345
myByteArray2=1,2,3,4,5
Autoscroll
Clear output
9600 baud
Newline
- Detach the Micro SD Card from the Micro SD Card module
- Insert the Micro SD Card to an USB SD Card reader
- Connect the USB SD Card reader to the PC
- Open the esp32.txt file on your PC, it looks like below
Video Tutorial
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