Example07

Reading digital PIN2 when hardware button is pressed

In this example we will use digital PIN2 as an input. The electronic schematic is shown in the following figure. We have added 10k Ohm resistor as the pull-down resistor, which is connected between GND and PIN2:

Breadboard view is shown in the following figure. The push button is added which puts +5V to the digital PIN2:

We attach additional input PIN2:

console.log("Enabling Push Button on pin 2");

board.pinMode(2, board.MODES.INPUT);

The code that reads the pin value and send it to client:

board.digitalRead(2, function(value) {

        if (value == 0) {

            console.log("LED off");

            board.digitalWrite(13, board.LOW);

            sendValueViaWebSocket("0");

        if (value == 1) {

            console.log("LED on");

            board.digitalWrite(13, board.HIGH);

            sendValueViaWebSocket("1");

On client side we first add the div to display messages in the html:

<div id="print1"></div>

State that we will declare strict mode in order to use classes:

<script type="text/javascript">

"use strict"; // in order to use clasess

Define the variable for divElement:

var divElement = document.getElementById("print1"); // variable for div object where the values will be printed (logged)

and then add function to write to div:

function log(msg) {

    divElement.innerHTML += "<div>" + msg + "</div>"; // we print it to div

On message we print the value to div:

ws.onmessage = function (event) {

    log(event.data);

We also add the message on disconnect:

ws.onclose = function (value) {

    log("Connection closed.");

The results of the messages in the GUI are shown in the next figure:

example07.js

var http = require("http").createServer(handler);

var fs = require("fs"); // variable for file system

var firmata = require("firmata");

const WebSocket = require('ws');

const wss = new WebSocket.Server({port: 8888});

var board = new firmata.Board("/dev/ttyACM0", function(){ // ACM Abstract Control Model for serial communication with Arduino (could be USB)

    console.log("Connecting to Arduino");

    console.log("Activation of Pin 13");

    board.pinMode(13, board.MODES.OUTPUT); // Configures the specified pin to behave either as an input or an output.

    console.log("Enabling pin 2 for button");

    board.pinMode(2, board.MODES.INPUT);

});

function handler(req, res) {

    fs.readFile(__dirname + "/example07.html",

    function (err, data) {

        if (err) {

            res.writeHead(500, {"Content-Type": "text/plain"});

            return res.end("Error loading html page.");

    res.writeHead(200);

    res.end(data);

});

http.listen(8080); // server will listen on port 8080 to serve html page

var sendValueViaWebSocket = function(){};

board.on("ready", function() {

wss.on('connection', function (ws) {

    ws.send("Server connected.");

  sendValueViaWebSocket = function(value) {

        ws.send(value);

}); // end of wss code

    board.digitalRead(2, function(value) {

        if (value == 0) {

            console.log("LED off");

            board.digitalWrite(13, board.LOW);

            sendValueViaWebSocket("0");

        if (value == 1) {

            console.log("LED on");

            board.digitalWrite(13, board.HIGH);

            sendValueViaWebSocket("1");

    }); // end of board digital read

});  // end of board.on "ready"

example07.html

<!DOCTYPE html>

<meta charset = utf8>

<html>

<head>

    <title>Example with HW button</title>

</head>

<body>

<div id="print1"></div>

<script type="text/javascript">

"use strict"; // in order to use clasess

var divElement = document.getElementById("print1"); // var for div el.

function log(msg) {

    divElement.innerHTML += "<div>" + msg + "</div>"; // print to div

var ws = new WebSocket('ws://192.168.254.149:8888/');

ws.onmessage = function (event) {

    log(event.data);

ws.onclose = function (value) {

    log("Connection closed.");

</script>

</body>

</html>

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