Arduino. Send text file from SD card to web server

Question

I have a, Arduino sketch that every 10 minutes, writes temprature data to SD text file and post that data to web server.

In case of internet connection loss, the sketch continues to save data to SD text file (but not post it to web). When the internet connection is back again, then I need to read entire text file from SD card and post it to the web server (a php script receive the posted content)

Using the following code I can post to php scripts. But now I need the postdata variable contains the text file.

          if (client.connect("192.168.1.100", 80))
          {
            client.println("POST /readfile.php HTTP/1.1");
            client.println("Host: 192.168.1.100");
            client.println("User-Agent: Arduino/1.0");
            client.println("Connection: close");            
            client.println("Content-Type: application/x-www-form-urlencoded");
            client.print("Content-Length: ");
            client.println(postdata.length());
            client.println("");
            client.println(postdata);
            delay(1);
            client.stop();

So I need a way to read the text file in a String (or whatever) variable.

I can use Arduino UNO, MEGA or ESP32 Thanks in advance!

score 3 · Accepted Answer · answered Apr 14 '20 at 08:19

Here is a complete code that works on ArduineIDE 1.8.12 with ESP8266 (core 1.6.3) or ESP32 (core 1.0.4) and uses the built in SD card.
As you gave no details to the structure of your data file the assumptions are

each data entry is in a line
the data structure within the line is processed on server
server expects and processes one data entry (= line) per transmisson

The code is commented so read those for details:

#include "FS.h"
#include "SD.h"
#include "SPI.h"
#ifdef ESP32
#include <WiFi.h>
#elif defined(ESP8266)
#include <ESP8266WiFi.h>
#endif

// function declaration
void postFileContent(const char * path );

#define FILE_LINE_LENGTH        81  // a line has 80 chars 
char txtLine[FILE_LINE_LENGTH];
char postdata [FILE_LINE_LENGTH];
bool readCondition = true;  // Has to be defined somewhere to trigger SD read

#ifdef ESP8266
const uint8_t chipSelect = 4;  //CS pin of the sd card reader
#endif
WiFiClient client;

void setup() {
  Serial.begin(115200);
#ifdef ESP32
  if (!SD.begin()) {
#elif defined(ESP8266)
  if (!SD.begin(chipSelect)) {
#endif
    Serial.println("Card reader mount failed");
    return;
  }
#ifdef ESP32
  uint8_t cardType = SD.cardType();
  if (cardType == CARD_NONE) {
    Serial.println("No SD card attached");
    return;
  }
#endif
}

void loop() {
  //...... Your program structure
  if (client.connect("192.168.1.100", 80)) {
    if (readCondition == true) {
      postFileContent("/data_log.txt"); // Read file data_log.txt in Root directory
      readCondition = false; // reset condition
    }
    else {
      client.println("POST /readfile.php HTTP/1.1");
      client.println("Host: 192.168.1.100");
      client.println("User-Agent: Arduino/1.0");
      client.println("Connection: close");
      client.println("Content-Type: application/x-www-form-urlencoded");
      client.print("Content-Length: ");
      client.println(strlen(postdata));
      client.println("");
      client.println(postdata);
    }
    delay(1);
    client.stop();
  }
  //...... Your program structure

}

void postFileContent(const char* path) {
  Serial.print(F(" -- Reading entries from file = "));
  Serial.print(path);
  if (!SD.exists(path)) {
    Serial.println("ERROR: The required file does not exist.");
    return;
  }
#ifdef ESP32
  File file = SD.open(path);
#elif defined(ESP8266)
  File file = SD.open(path, FILE_READ); // FILE_READ is default so not realy needed but if you like to use this technique for e.g. write you need FILE_WRITE
#endif
  if (!file) {
    Serial.println("Failed to open file for reading");
    return;
  }
  char c;
  uint8_t i = 0;

  while (file.available()) {
    c = file.read();
    if (c == '\n') { //Checks forline break
      txtLine[i] = '\0';
      Serial.print(F(" * "));
      Serial.println(txtLine); //This is where you get one line of file at a time.
      client.println("POST /readfile.php HTTP/1.1");
      client.println("Host: 192.168.1.100");
      client.println("User-Agent: Arduino/1.0");
      client.println("Connection: close");
      client.println("Content-Type: application/x-www-form-urlencoded");
      client.print("Content-Length: ");
      client.println(strlen(txtLine));
      client.println("");
      client.println(txtLine);
    }
    else if (c >= 32) {
      txtLine[i] = c;
      i++;
    }
  }
  file.close();
  Serial.println(F("DONE Reading"));
}

Hope this get you started

How to incorporate ota bin files (multupart) from network using your solution? — Shariq Azim, Apr 12 '21 at 12:41

Arduino. Send text file from SD card to web server

1 Answers1