ESP8266 - Read Config from SD Card

This tutorial guides you through the utilization of a config file on a Micro SD Card with ESP8266, encompassing the following aspects:

ESP8266 NodeMCU Micro SD Card Config File

Hardware Preparation

1×ESP8266 NodeMCU
1×Micro USB Cable
1×Micro SD Card
1×Micro SD Card Module
1×Jumper Wires
1×USB 3.0 SD Card Reader
1×(Optional) 5V Power Adapter for ESP8266
1×(Optional) ESP8266 Screw Terminal Adapter

Or you can buy the following sensor kit:

1×DIYables Sensor Kit 30 types, 69 units
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Overview of Micro SD Card Module

If you are unfamiliar with the Micro SD Card Module, including its pinout, how it works, and how to program it, then check out the ESP8266 - Micro SD Card tutorial.

How It Works

Each key-value pair is held on a single line of the Micro SD Card, with the key and value divided by an = character. Additionally, each pair is separated from the others by a newline character.

The ESP8266 code will look for the key and locate the associated value, storing it in a variable. This variable can be an int, float, or String.

Wiring Diagram

The wiring diagram between ESP8266 NodeMCU and Micro SD Card Module

This image is created using Fritzing. Click to enlarge image

See more in ESP8266's pinout and how to supply power to the ESP8266 and other components.

※ NOTE THAT:

If you have an Ethernet shield or any other shield that includes a Micro SD Card Holder, you don't need to use the Micro SD Card Module. Simply insert the Micro SD Card into the Holder on the shield.

How To read config to variables

  • Generate a config.txt file on your PC using Notepad or Notepad++.
  • Copy and paste the following key-value pairs into the config.txt:
myString_1=Hello myString_2=newbiely.com myInt_1=2 myInt_2=-105 myFloat_1=0.74 myFloat_2=-46.08
  • Attach the Micro SD Card to the PC through a USB 3.0 SD Card Reader.
  • Ensure that the Micro SD Card is formatted FAT16 or FAT32 (look up instructions online).
  • Place the config.txt file in the main directory of the Micro SD Card.
  • Once finished, unplug the Micro SD Card from the PC.
  • Connect the Micro SD Card to the ESP8266 using the Micro SD Card Module as per the wiring diagram.
  • Copy the code given below and open it with the Arduino IDE.
/* * This ESP8266 NodeMCU code was developed by newbiely.com * * This ESP8266 NodeMCU code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/esp8266/esp8266-read-config-from-sd-card */ #include <SD.h> #define PIN_SPI_CS D8 #define FILE_NAME "config.txt" #define KEY_MAX_LENGTH 30 // change it if key is longer #define VALUE_MAX_LENGTH 30 // change it if value is longer // variables int myInt_1; int myInt_2; float myFloat_1; float myFloat_2; String myString_1; String myString_2; void setup() { Serial.begin(9600); if (!SD.begin(PIN_SPI_CS)) { Serial.println(F("SD Card failed, or not present")); while (1); // don't do anything more: } Serial.println(F("SD Card initialized.")); myInt_1 = SD_findInt(F("myInt_1")); myInt_2 = SD_findInt(F("myInt_2")); myFloat_1 = SD_findFloat(F("myFloat_1")); myFloat_2 = SD_findFloat(F("myFloat_2")); myString_1 = SD_findString(F("myString_1")); myString_2 = SD_findString(F("myString_2")); Serial.print(F("myInt_1 = ")); Serial.println(myInt_1); Serial.print(F("myInt_2 = ")); Serial.println(myInt_2); Serial.print(F("myFloat_1 = ")); Serial.println(myFloat_1); Serial.print(F("myFloat_2 = ")); Serial.println(myFloat_2); Serial.print(F("myString_1 = ")); Serial.println(myString_1); Serial.print(F("myString_2 = ")); Serial.println(myString_2); } void loop() { } bool SD_available(const __FlashStringHelper * key) { char value_string[VALUE_MAX_LENGTH]; int value_length = SD_findKey(key, value_string); return value_length > 0; } int SD_findInt(const __FlashStringHelper * key) { char value_string[VALUE_MAX_LENGTH]; int value_length = SD_findKey(key, value_string); return HELPER_ascii2Int(value_string, value_length); } float SD_findFloat(const __FlashStringHelper * key) { char value_string[VALUE_MAX_LENGTH]; int value_length = SD_findKey(key, value_string); return HELPER_ascii2Float(value_string, value_length); } String SD_findString(const __FlashStringHelper * key) { char value_string[VALUE_MAX_LENGTH]; int value_length = SD_findKey(key, value_string); return HELPER_ascii2String(value_string, value_length); } int SD_findKey(const __FlashStringHelper * key, char * value) { File configFile = SD.open(FILE_NAME); if (!configFile) { Serial.print(F("SD Card: error on opening file ")); Serial.println(FILE_NAME); return; } char key_string[KEY_MAX_LENGTH]; char SD_buffer[KEY_MAX_LENGTH + VALUE_MAX_LENGTH + 1]; // 1 is = character int key_length = 0; int value_length = 0; // Flash string to string PGM_P keyPoiter; keyPoiter = reinterpret_cast<PGM_P>(key); byte ch; do { ch = pgm_read_byte(keyPoiter++); if (ch != 0) key_string[key_length++] = ch; } while (ch != 0); // check line by line while (configFile.available()) { int buffer_length = configFile.readBytesUntil('\n', SD_buffer, 100); if (SD_buffer[buffer_length - 1] == '\r') buffer_length--; // trim the \r if (buffer_length > (key_length + 1)) { // 1 is = character if (memcmp(SD_buffer, key_string, key_length) == 0) { // equal if (SD_buffer[key_length] == '=') { value_length = buffer_length - key_length - 1; memcpy(value, SD_buffer + key_length + 1, value_length); break; } } } } configFile.close(); // close the file return value_length; } int HELPER_ascii2Int(char *ascii, int length) { int sign = 1; int number = 0; for (int i = 0; i < length; i++) { char c = *(ascii + i); if (i == 0 && c == '-') sign = -1; else { if (c >= '0' && c <= '9') number = number * 10 + (c - '0'); } } return number * sign; } float HELPER_ascii2Float(char *ascii, int length) { int sign = 1; int decimalPlace = 0; float number = 0; float decimal = 0; for (int i = 0; i < length; i++) { char c = *(ascii + i); if (i == 0 && c == '-') sign = -1; else { if (c == '.') decimalPlace = 1; else if (c >= '0' && c <= '9') { if (!decimalPlace) number = number * 10 + (c - '0'); else { decimal += ((float)(c - '0') / pow(10.0, decimalPlace)); decimalPlace++; } } } } return (number + decimal) * sign; } String HELPER_ascii2String(char *ascii, int length) { String str; str.reserve(length); str = ""; for (int i = 0; i < length; i++) { char c = *(ascii + i); str += String(c); } return str; }
  • Click the Upload button on the Arduino IDE to send the code to the ESP8266.
  • Check the Serial Monitor for the outcome.
COM6
Send
SD Card initialized. myInt_1 = 2 myInt_2 = -105 myFloat_1 = 0.74 myFloat_2 = -46.08 myString_1 = Hello myString_2 = newbiely.com
Autoscroll Show timestamp
Clear output
9600 baud  
Newline  
  • The Serial Monitor displays the values of variables that are the same as those stored on the micro SD Card.

You can now alter the code in order to include additional variables.

※ NOTE THAT:

The code does not take into account the arrangement of key-value pairs. It will search from the start to the end of the file until the key is found.

Video Tutorial