I'm trying to push some data to ThingSpeak using the EtherCard library with the ENC28J60 ethernet module.

At the moment I'm using the exemple code that comes with the library just for tests. But no matter what I do, always receive the same reply:

REPLY recieved....
HTTP/1.1 400 Bad Request
Date: Sat, 09 Mar 2019 17:26:52 GMT
Content-Type: text/html; charset=utf-8
Transfer-Encoding: chunked
Connection: close
Status: 400 Bad Request
X-Frame-Options: SAMEORIGIN
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: GET, POST, PUT, OPTIONS, DELETE, PATCH
Access-Control-Allow-Headers: origin, content-type, X-Requested-With
Access-Control-Max-Age: 1800
Cache-Control: no-cache
Set-Cookie: request_method=POST; path=/
X-Request-Id: 9184d325-402d-4512-a942-e7


#include <EtherCard.h>

// Simple demo for feeding some random data to Pachube.
// 2011-07-08 <jc@wippler.nl>
// License: GPLv2

// Handle returning code and reset ethernet module if needed
// 2013-10-22 hneiraf@gmail.com

// Modifing so that it works on my setup for www.thingspeak.com.
// Arduino pro-mini 5V/16MHz, ETH modul on SPI with CS on pin 10.
// Also added a few changes found on various forums. Do not know what the
// res variable is for, tweaked it so it works faster for my application
// 2015-11-09 dani.lomajhenic@gmail.com

// change these settings to match your own setup
//#define FEED "000"
#define APIKEY "XXXXXXXXXXXX" // put your key here

// ethernet interface mac address, must be unique on the LAN
static byte mymac[] = { 0x74,0x69,0x69,0x2D,0x30,0x32 };
const char website[] PROGMEM = "api.thingspeak.com";
byte Ethernet::buffer[700];
uint32_t timer;
Stash stash;
byte session;

//timing variable
int res = 100; // was 0

void setup () {
  Serial.println("\n[ThingSpeak example]");

  //Initialize Ethernet

void loop () {
  //if correct answer is not received then re-initialize ethernet module
  if (res > 220){

  res = res + 1;


  //200 res = 10 seconds (50ms each res)
  if (res == 200) {

    //Generate random info
    float demo = random(0,500);
    //word one = random(0,500);
    //String msje;

//    if (demo < 250){
//      msje = "low";
//    }
//    else{
//      msje = "high";
//    }

    // generate two fake values as payload - by using a separate stash,
    // we can determine the size of the generated message ahead of time
    // field1=(Field 1 Data)&field2=(Field 2 Data)&field3=(Field 3 Data)&field4=(Field 4 Data)&field5=(Field 5 Data)&field6=(Field 6 Data)&field7=(Field 7 Data)&field8=(Field 8 Data)&lat=(Latitude in Decimal Degrees)&long=(Longitude in Decimal Degrees)&elevation=(Elevation in meters)&status=(140 Character Message)
    byte sd = stash.create();

    //Display data to be sent

    // 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 /update HTTP/1.1" "\r\n"
      "Host: $F" "\r\n"
      "Connection: close" "\r\n"
      "X-THINGSPEAKAPIKEY: $F" "\r\n"
      "Content-Type: application/x-www-form-urlencoded" "\r\n"
      "Content-Length: $D" "\r\n"
    website, PSTR(APIKEY), stash.size(), sd);

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

 // added from: http://jeelabs.net/boards/7/topics/2241
 int freeCount = stash.freeCount();
    if (freeCount <= 3) {   Stash::initMap(56); }

   const char* reply = ether.tcpReply(session);

   if (reply != 0) {
     res = 0;
     Serial.println(F(" >>>REPLY recieved...."));

void initialize_ethernet(void){
  for(;;){ // keep trying until you succeed
    //Reinitialize ethernet module
    //pinMode(5, OUTPUT);  // do notknow what this is for, i ve got something elso on pin5
    //Serial.println("Reseting Ethernet...");
    //digitalWrite(5, LOW);
    //digitalWrite(5, HIGH);

    // Change 'SS' to your Slave Select pin, if you arn't using the default pin
    if (ether.begin(sizeof Ethernet::buffer, mymac, SS) == 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);

    //reset init value
    res = 180;

I searched the site and saw that the Bad Request is related to syntax error.

Any attempt I made was in this part of the code, almost every change I tried was on the first line:

Stash::prepare(PSTR("POST /update HTTP/1.1" "\r\n"
      "Host: $F" "\r\n"
      "Connection: close" "\r\n"
      "X-THINGSPEAKAPIKEY: $F" "\r\n"
      "Content-Type: application/x-www-form-urlencoded" "\r\n"
      "Content-Length: $D" "\r\n"
    website, PSTR(APIKEY), stash.size(), sd);

I think that is the part responsible for the URL syntax.

I tried to change the POST for GET, to put all the URL on the first line, something like: "POST https://$F/update?api_key=$F HTTP/1.1"(that one I saw on StackOverflow).

But I don't have any more idea where is the problem.

To confirm that the channel is OK I tried to send data directly via URL, and everything is OK.

URL Exemple:


I don't know what to do to get it work. Thanks for your help!

  • Please add info/link to the library and the example. Also high-light any changes you might have done. – Mikael Patel Mar 10 at 13:20
  • If your GET request https://api.thingspeak.com/update?api_key=XXXXXXXXXXXXX&field1=0 works, but the POST request is not, the only thing that could be incorrect is your payload sent by POST request. that is, the value of sd. If you print it out, what do you see? – hcheung Mar 11 at 9:49
  • Generates a float like 307.0. I tested the URL with this value and worked. I tested the URL manually, just put the URL on the browser. When i changed on the code to GET doesn't worked too – Shinforinpola Mar 12 at 2:52

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