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Topic: JSON WEB SERVER html (Read 7 times) previous topic - next topic


Hi everyone,

First of all, I want to apologize if this is not the correct place to post, and secondly as you notice my english it is not so good.

I hope you could help me. I want to show in a web page the values of my sensors. By now I am playing with a little example.

The system is composed by an arduino UNO and an Ethernet shield. Both work as a server. I made a "web page" in html:

<!DOCTYPE html>
  function loadJson(fioNumber)  {
    var oJSON = new XMLHttpRequest();
    oJSON.open("GET","&fio" + fioNumber,true);
    oJSON.onreadystatechange = function()  {
      if (oJSON.readyState == 4)  {
        var json = eval("(" + oJSON.responseText + ")");
        document.getElementById("temperature").innerHTML = json.variables.temperature;
        document.getElementById("humidity").innerHTML    = json.variables.humidity;
        document.getElementById("address").innerHTML     = json.variables.address;
        document.getElementById("sleepCycle").innerHTML  = json.variables.sleepCycle;
        document.getElementById("asynchronus").innerHTML = json.variables.asynchronus;
        document.getElementById("name").innerHTML        = json.name;
<title>Servidor Web Arduino</title>


<p><INPUT TYPE=BUTTON OnClick="loadJson(1);" VALUE=FIO1></p>
<p>   name:        <div id="name"></div></p>
<p>   temperature: <div id="temperature"></div></p>
<p>   humidity:    <div id="humidity"></div></p>
<p>   address:     <div id="address"></div></p>
<p>   sleepCycle:  <div id="sleepCycle"></div></p>
<p>   asynchronus: <div id="asynchronus"></div></p>


I want to explain this, I create as files as sensors. If I have 4 sensors there are 4 files F1.txt,F2.txt,F3.txt,F4.txt. Itl would be sense with the sketch.

It is supposed that if a push the button, a http get request is sent to my board. And then it replies with a json object:
(this structure is saved as a file )
  "name": "fio1"
     "address": "0x01",
          "temperature": "24",
          "humidity": "85",
          "asynchronus": "0",
          "sleepCycle": "20"

And I think when it is send to the browser it will work... I show you my super-sketch:


#include <SPI.h>
#include <Ethernet.h>

#include <SD.h>  // ocupa 5KB 

char fio[3];
byte mac[] = { 0x90, 0xA2, 0xDA, 0x00, 0x49, 0xFD };
byte ip[]  = { 192, 168, 1, 2 }; //aula de informática {172,31,55,44} // laboratorio { 192, 168, 112, 31 }
byte gateway[] = { 192, 168, 1, 1};
Server server(80); // Puerto 80, HTTP


//Ethernet Shield uses pins 10,11,12,13.
#define bufferMax 128
int bufferSize;
char buffer[bufferMax];

// SD
File myFile;

#define ssPin       10
#define chipSelect   4

void setup() {

  Ethernet.begin(mac, ip, gateway);
  Serial.begin(9600);    // inicia comunicación serie

  if (!SD.begin(chipSelect)) {  // inicia la tarjeta SD
    Serial.println("initialization failed!");

void loop() {


void listenForClient() {

  Client client = server.available(); // espera a que haya datos disponilbles
  if ( client ) {
    int fioNumber = parseReceivedRequest(client);
    if (fioNumber != 0)
      sendGetResponse(fioNumber, client); 

void waitForRequest(Client client) {
  bufferSize = 0;
  while (client.connected()) {
    if (client.available()) {
      char c = client.read();
      if (c == '\n')
        if (bufferSize < bufferMax)
          buffer[bufferSize++] = c;

int parseReceivedRequest(Client client) { // Petición recibida del tipo: "GET &fio1 HTTP/1.1"
  char* qm, * space;
   // strncpy does not automatically add terminating zero, but strncat does! So start with blank string and concatenate.
  if ( qm = strstr(buffer, "&fio") ) {  //apuntará a &
    qm     += 4; // sumando 5 apunta al valor deseado ( 4 letras --> "&", "f", "i", "o")
    space  = strstr(qm, " ") + 1;
    strncat(fio, qm, space-qm-5);
    return atoi(fio);
  } else if ( qm = strstr(buffer, " ") ) {
           return 0;
         }  else
              return 0;

void sendGetResponse(int fioNumber, Client client) {
  client.println("HTTP/1.1 200 OK");
  client.println("Content-Type: text/plain");
  char filename[8];
  sprintf (filename, "F%d.jsn", fioNumber);
  filePrint(filename, client);
  client.println(" ");
void webPrint (Client client) { 
  filePrint("SERVER.TXT", client);
  char filename[6];
  int fiolength =  1, i = 1;
  for ( i = 1; i <= fiolength; i++ ) {
    sprintf (filename, "F%d.txt", i);
    filePrint (filename, client);
// fuente: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1295739118
void filePrint (char filename[10], Client client){
  char a;
  if (myFile = SD.open(filename, FILE_READ)) { 
    while ( myFile.available() ) {
      a = (char)myFile.read();
    myFile.close();                 // CERRAR FICHERO

basically I wait for http request, I write http:\\ in the browser... so I received "GET /HTTP1.1" as there is not information I print the web page. Then I wait  for clicking the button, so it will appear an GET fio1 /HTTP1.1. I parse this last one, and response to it. I search on the micro SD card for a file called fio1 and then print this information that is the json structure  and nothing happens. The goal was  when the structure arrives to the client the script execute itself and fill the gap I wrote as <div ahref ... .... but... Maybe I make a  mistake writing the html or the script or the http json response is not the correct one...

I am sorry it is sort of big... xD. Well, my questions are:

I do not have idea of html or http, just the few things I´ve read. And it is a mess. So I am not know if the html is well proposed. Or if I can response the http get request as I did just printing on the client, ...

I hope you could help me! Just read this is remarkable.

thank you !


I'm no pro but, here's an idea that may simplify the matter. You want the arduino to become the server? I think that's kinda much for the little guy. Why not send the sensor readings to the PC and "processing" can send them to the webpage that is hosted by that PC. By send I mean write into a file and the Website will refresh the read on the file at a few secs interval. Hope this helps a little, if not sorry for me posting.



thanks for your answer. The next step it will be to use a server, as you said. But I was asked to do this more or less... Just show the information. There is other examples, like ajaxwebserver I found it here ->http://djgj.sub.jp/TETRASTYLE/arduino/Ajax_WebServer.txt

As you can see, the html it is not complicated. And json is supposed to do easier. But anyway thank you for your answer.



As I understand it, you have a local web page that provides all the decorative stuff and just executes an HTTP request to the Arduino to retrieve some data. The page then processes the results and uses that to populate the page.

The basic approach seems OK. I haven't look at the detail of your JSON handling, but your JSON fragment is incorrect: the field names should not be quoted.

I suggest you get that sorted out by hard-coding your JSON string in the page and then use your existing logic to exec it into a variable; then you can print out whatever fields of that variable interest you.
I only provide help via the forum - please do not contact me for private consultancy.


I want to show in a web page the values of my sensors.

The below is a more conventional and possibly easier method to display values in a web page.

Code: [Select]

// arduino IDE 1.0
// for W5100 ethernet shield
// the IP address will be dependent on your local network/router
// port 80 is default for HTTP, but can be changed as needed
// use IP address like in your brouser
// or http://zoomkat.no-ip.com:84 with dynamic IP service
// use the \ slash to escape the " in the html
// meta refresh set for 2 seconds

#include <SPI.h>
#include <Ethernet.h>

int x=0; //set refresh counter to 0
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
IPAddress ip(192,168,1,102); // ip in lan
EthernetServer server(84); //server is using port 84

void setup()
  // start the server
  Ethernet.begin(mac, ip);

void loop()
  // listen for incoming clients
  EthernetClient client = server.available();
  if (client) {
     while (client.connected()) {
      if (client.available()) {
        char c = client.read();
        // see if HTTP request has ended with blank line
        if (c == '\n') {
          // send a standard http response header
          client.println("HTTP/1.1 200 OK");
          client.println("Content-Type: text/html");
          //meta-refresh page every 2 seconds
          client.print("<meta http-equiv=\"refresh\" content=\"2\">");
          client.print("<TITLE />Zoomkat's meta-refresh test</title>");
          client.print("Zoomkat's meta-refresh test IDE 1.0");
          client.println("<br />");
          client.print("page refresh number ");
          client.println(x); //current refresh count
          client.println("<br />");
          client.println("<br />");
          client.print("Zoomkat's arduino analog input values:");
          client.println("<br />");
          client.println("<br />");
          // output the value of each analog input pin
          for (int analogChannel = 0; analogChannel < 6; analogChannel++) {
            client.print("analog input ");
            client.print(" is ");
            client.println("<br />");
    // give the web browser time to receive the data
    // close the connection:

Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   8)

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