Sending HTTP POST Request with Arduino and ENC28J60 Ethernet LAN Network Module

First of all you need to install following library: https://github.com/jcw/ethercard

connect your module to arduino with 6 pins:

• ENC SO -> Arduino pin 12
• ENC SI -> Arduino pin 11
• ENC SCK -> Arduino pin 13
• ENC CS -> Arduino pin 8
• ENC VCC -> Arduino 3V3 pin
• ENC GND -> Arduino Gnd pin

then use following code:

#include <EtherCard.h>

// your variable

#define PATH    "example.php"
#define VARIABLE    "test"

// ethernet interface mac address, must be unique on the LAN
byte mymac[] = { 0x74,0x69,0x69,0x2D,0x30,0x31 };

char website[] PROGMEM = "www.mydomain.com";

byte Ethernet::buffer[700];
uint32_t timer;
Stash stash;

void setup () {
  Serial.begin(57600);
  Serial.println("\n[webClient]");

  if (ether.begin(sizeof Ethernet::buffer, mymac) == 0) 
    Serial.println( "Failed to access Ethernet controller");
  if (!ether.dhcpSetup())
    Serial.println("DHCP failed");

  ether.printIp("IP:  ", ether.myip);
  ether.printIp("GW:  ", ether.gwip);  
  ether.printIp("DNS: ", ether.dnsip);  

  if (!ether.dnsLookup(website))
    Serial.println("DNS failed");

  ether.printIp("SRV: ", ether.hisip);
}

void loop () {
  ether.packetLoop(ether.packetReceive());

  if (millis() > timer) {
    timer = millis() + 10000;

    byte sd = stash.create();
    stash.print("variable=");
    stash.print(VARIABLE);
    stash.print("&action=Submit");
    stash.save();

    // generate the header with payload - note that the stash size is used,
    // and that a "stash descriptor" is passed in as argument using "$H"
    Stash::prepare(PSTR("POST http://$F/$F.csv HTTP/1.0" "\r\n"
                "Host: $F" "\r\n"
                "Content-Length: $D" "\r\n"
                "Content-Type: application/x-www-form-urlencoded" "\r\n"
                "\r\n"
                "$H"),
    website, PSTR(PATH), website, stash.size(), sd);

    // send the packet - this also releases all stash buffers once done
    ether.tcpSend();
  }
}

Arduino v1.6.12

 #include <EtherCard.h>

// your variable

#define PATH    "example.php"
#define VARIABLE    "test"

// ethernet interface mac address, must be unique on the LAN
byte mymac[] = { 0x74,0x69,0x69,0x2D,0x30,0x31 };

const char website[] PROGMEM = "www.google.com";

byte Ethernet::buffer[700];
uint32_t timer;
Stash stash;

void setup () {
  Serial.begin(57600);
  Serial.println("\n[webClient]");

  if (ether.begin(sizeof Ethernet::buffer, mymac) == 0) 
    Serial.println( "Failed to access Ethernet controller");
  if (!ether.dhcpSetup())
    Serial.println("DHCP failed");

  ether.printIp("IP:  ", ether.myip);
  ether.printIp("GW:  ", ether.gwip);  
  ether.printIp("DNS: ", ether.dnsip);  

  if (!ether.dnsLookup(website))
    Serial.println("DNS failed");

  ether.printIp("SRV: ", ether.hisip);
}

void loop () {
  ether.packetLoop(ether.packetReceive());

  if (millis() > timer) {
    timer = millis() + 10000;

    byte sd = stash.create();
    stash.print("variable=");
    stash.print(VARIABLE);
    stash.print("&action=Submit");
    stash.save();

    // generate the header with payload - note that the stash size is used,
    // and that a "stash descriptor" is passed in as argument using "$H"
    Stash::prepare(PSTR("POST http://$F/$F.csv HTTP/1.0" "\r\n"
                        "Host: $F" "\r\n"
                        "Content-Length: $D" "\r\n"
                        "\r\n"
                        "$H"),
            website, PSTR(PATH), website, stash.size(), sd);

    // send the packet - this also releases all stash buffers once done
    ether.tcpSend();
  }
}

If anyone is looking to call an API, you need to remove .csv in the request, Like this:

 byte sd = stash.create();
    stash.print("variable="); //change this to your post variable
    stash.print(VARIABLE);
    stash.print("&action=Submit");
    stash.save();
// generate the header with payload - note that the stash size is used,
// and that a "stash descriptor" is passed in as argument using "$H"
//remove the .csv
Stash::prepare(PSTR("POST http://$F/$F HTTP/1.0" "\r\n"
            "Host: $F" "\r\n"
            "Content-Length: $D" "\r\n"
            "Content-Type: application/x-www-form-urlencoded" "\r\n"
            "\r\n"
            "$H"),
website, PSTR(PATH), website, stash.size(), sd);

Additional information, if you are using local server to test, you can view the Access Log of Wampp or Xampp Server to know weather your request has reached the server or not.

And use const in this line:

char const website[] PROGMEM = "www.mydomain.com";