Arduino。将文本文件从SD卡发送到Web服务器

Question

我有一个Arduino草图，每10分钟将温度数据写入SD文本文件，并将该数据发布到Web服务器。

如果失去互联网连接，草图将继续将数据保存到SD文本文件（但不会将其发布到Web）。当互联网重新恢复连接时，我需要从SD卡读取整个文本文件并将其发布到Web服务器（PHP脚本接收发布的内容）

使用以下代码，我可以发布到php脚本。但是现在我需要postdata变量包含文本文件。

          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();

所以我需要一种方法来读取String（或其他）变量中的文本文件。

我可以使用Arduino UNO，MEGA或ESP32预先感谢！

Answer 1

这里是完整的代码，可在带有ESP8266（核心1.6.3）或ESP32（核心1.0.4）的ArduineIDE 1.8.12上使用并使用内置的SD卡。由于您未提供数据文件结构的详细信息，因此假设是

• 每个数据条目都在一行中
• 该行中的数据结构在服务器上处理
• 服务器每次传输期望并处理一个数据条目（=行）

该代码已注释，请阅读详细内容：

#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"));
}

希望这可以帮助您入门