I'm trying to send data from my ESP8266 to a NodeJS TCP server, the connection and basic charakters (48-90) are working fine, but if I use others like ASCII-Code (0,1,2,3...) I don't get any usefull data out of it. So what I was thinking about that there are some character which aren't allowed to send over TCP/IP.

By the way, I'm using this to write to the server, and I work with the standard WiFi Client library

char arr[255]
for(int i = 0; i < 255; i++){
   arr[i] = (char)i;

Nodejs File:

// Load the TCP Library
net = require('net');

var mysql = require('mysql');

// Keep track of the chat clients
var clients = [];
var uploadCounter = 0;


// Start a TCP Server
net.createServer(function (socket) {

    // Identify this client
    socket.name = socket.remoteAddress + ":" + socket.remotePort

    // Put this new client in the list

    // Send a nice welcome message and announce
    socket.write("Welcome " + socket.name + "\n");
    broadcast(socket.name + " connected\n", socket);

    // Handle incoming messages from clients.
    socket.on('data', function (data) {
        broadcast(">> " + data, socket);


    // Remove the client from the list when it leaves
    socket.on('end', function () {
        clients.splice(clients.indexOf(socket), 1);
        broadcast(socket.name + " disconnected.\n\n");

    // Send a message to all clients
    function broadcast(message, sender) {
        clients.forEach(function (client) {
            // Don't want to send it to sender
            if (client === sender) return;
        // Log it to the server output too


// Put a friendly message on the terminal of the server.
console.log("Chat server running at port 10101\n");

var connection;
function initMySQLConnection() {
    connection = mysql.createConnection({
        host: "host",
        user: "user",
        password: "pass",
        database: "database"

    connection.connect(function (err) {              
        if (err) {                                     
            console.log('error when connecting to db:', err);

    connection.on('error', function (err) {
        console.log('db error', err);
        if (err.code === 'PROTOCOL_CONNECTION_LOST') { // Connection to the MySQL server is usually
                                    // lost due to either server restart, or a
        } else {                                      // connnection idle timeout (the wait_timeout
            throw err;                                  // server variable configures this)

    setInterval(function () {
        connection.query('SELECT 1');
    }, 60000);

function uploadData(data) {
    data = String(data);

    console.log("Package Length: " + data.length);
    console.log("GOT ASCII CODE: ");
    for (var i = 0; i < 255; i++) {

    //upload Code
  • what does this mean? ... I don't get any usefull data out of it ................ what are you expecting for ASCII-Code (0,1,2,3...)? – jsotola Jan 24 at 7:22

The print function takes an array of characters as zero terminated c-string. It prints until a byte with value 0. You have zero at arr[0] so it is an empty string.

To send bytes, write function is used. The print functions convert parameters to text or expect text as zero terminated char array.

In your case it should be client.write(arr, length); where length is the number of bytes you want to send from the buffer arr.

  • now I get values from 0-127 but all above is 65533. so the error seems to be in my nodejs file, i will add it above – Ribisl Jan 24 at 9:33
  • ASCII code are only until 127. why do you read it as String and chars? – Juraj Jan 24 at 10:07
  • Doesnt the extended ascii code go until 255? – Ribisl Jan 24 at 10:14
  • tell it to data.charCodeAt(i) :-) – Juraj Jan 24 at 10:21
  • So you mean without the data = String(data)? – Ribisl Jan 24 at 10:23

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.