This is a sample of reading and writing a text file saved in an SD card with ESP32.
I couldn't find much simple sample code on the net to read and write, so I drew it.
I used this site as a reference for wiring between the SD card and ESP.
And I used this code as a reference.
Save data to SD card with Arduino
Reference: mgo-tec電子工作
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| #include <SD.h> | |
| #define LOG_FILE_NAME "/log.txt" | |
| const uint8_t SD_CS = 5; // GPIO5=CS | |
| static File s_myFile; | |
| void SD_init() | |
| { | |
| Serial.print("Initializing SD card..."); | |
| if (!SD.begin(SD_CS)) { | |
| Serial.println("initialization failed!"); | |
| return; | |
| } | |
| Serial.println("initialization done."); | |
| } | |
| String SD_read() { | |
| String str; | |
| File file = SD.open(LOG_FILE_NAME, FILE_READ); | |
| if(file){ | |
| //---1byteずつ読み込んだ文字を結合 | |
| while (file.available()) { | |
| str += char(file.read()); | |
| } | |
| } else{ | |
| Serial.println(" error..."); | |
| } | |
| //---ファイルを閉じる | |
| file.close(); | |
| return str; | |
| } | |
| void SD_write() | |
| { | |
| String backLog = SD_read(); | |
| s_myFile = SD.open(LOG_FILE_NAME, FILE_WRITE); | |
| if (s_myFile) { | |
| Serial.print("Writing to test.txt..."); | |
| s_myFile.print(backLog); | |
| s_myFile.println("Hello, World"); | |
| s_myFile.close(); | |
| Serial.println("done."); | |
| } else { | |
| Serial.println("error opening test.txt"); | |
| } | |
| } | |
| void setup() { | |
| Serial.begin(115200); | |
| while(!Serial); | |
| Serial.println(); | |
| SD_init(); | |
| SD_write(); | |
| Serial.println(SD_read()); | |
| } | |
| void loop() { | |
| // put your main code here, to run repeatedly: | |
| } |