ECE497 Project: Node.js Weather Station

Revision as of 23:32, 18 February 2012 by Ziyi Zhang (talk | contribs)
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Team members: Yuming Cao, Ziyi Zhang

Executive Summary

Our project aims to implement the emerging nodejs technique (the server side javascript) as a lightweight web server on the beagleboard and accomplish a series of remote monitoring and control of hardware pins like gpio/led/i2c on the beagleboard. We also tried to make our web server send automatic email when temperature goes too high. There are a lot of things we can do on the nodejs web server, but we try to make it related to our beagleboard hardware interface.

The automatic email sender is not working correctly. More work needs to be done to set a proper configuration to the SMTP server 'postfix'.

End with a two sentence conclusion.

The sentence count is approximate and only to give an idea of the expected length.

Installation Instructions

1. Here's our github path that includes everything useful to our project:

2. Additional packages installed via opkg:

  • install nodejs
opkg update
opkg install nodejs
opkg install nodejs-dev
  • install node package manager
curl | sh
  • install module
npm install
  • install binary module
npm install binary
  • install mailer module
npm install mailer
  • install SMTP server postfix

Go to [1] download the source of postfix, then unzip the .gz file, then run 'make', then run

sh postfix-install
  • Here's the guideline to install Cloud9 easily: [2]

User Instructions

Once everything is installed, how do you use the program? Give details here, so if you have a long user manual, link to it here.


Here is where you brag about what your project can do.

Consider including a YouTube demo.

Theory of Operation

Give a high level overview of the structure of your software. Are you using GStreamer? Show a diagram of the pipeline. Are you running multiple tasks? Show what they do and how they interact.

To build a web server, we need, in essence, both client side and server side scripts. Client side scripts mainly just involve ordinary javascripts that can be embedded in HTML file; while at the server-side, we adopt the emerging node.js, which is a really simple server side script that accomplishes equivalent tasks like ASP, PHP will do, but with even simpler implementation details.

Work Breakdown

1. We've already successfully using JavaScript read and write data to the linux gpio file.

fs.writeFileSync("/sys/class/leds/beagleboard::usr0/trigger", "heartbeat");
fs.writeFileSync("/sys/class/gpio/export", ""+5);

2. Even though we can access to the gpio in the above way, we still need to find someway to access the I2C information. In the I2C exercises, from the C code provided in exercise 5, we can think of the following two options:

a) To translate tons of the C codes into JavaScript...including rewriting the union structures like i2c_smbus_write_byte() and i2c_smbus_read_byte(), which requires far more knowledge in understanding how to translate the underlying hardware detail into upper-level script languages...

b) Try to run the ./myi2c excutable file directly inside nodjs script...

  • It seems that the second way is easier... We've already found a method... We're working on this... turns out this does not work for some reason.
  • At last we successfully excute the ./myi2c file inside our javascript using the following code, the big idea is create another child process to handle it:
var exec  = require('child_process').exec,
child = exec('./myi2c',
  function (error, stdout, stderr) {
    console.log('stdout:', stdout);
    console.log('stderr:', stderr);
    if (error !== null) {
      console.log('exec error:', error);

And the terminal will show the temperature.

3. Now we are going to working on how to show this temperature information on the website so that we can visit it from any place!!!

  • I've successfully done it!!! The pics are already uploaded to the github. Check the following code:
var fs = require("fs");
var http = require("http");

try {
	http.createServer(function(request, response) {

		response.writeHead(200, {"Content-Type": "text/plain"});
		var exec = require('child_process').exec, child;
		child = exec('./myi2c',
	    		function (error, stdout, stderr) {
				console.log('stdout:', stdout);
				console.log('stderr:', stderr);
				if(error != null) {
					console.log('exec error:', error);
} catch(ex3) {

4. The next thing we will do is to refresh the website every other time...

  • We are now able to load html file inside nodejs scripts so that we can put normal HTML stuff inside the web page and load it from server scripts. The following code snippet can accomplish this (borrowed and modified based on Jadon's code):
function loadHTMLFile(uri, res, temp) {
 var filename = path.join(process.cwd(), uri);
  function(exists) {
   if(!exists) {
    res.writeHead(404, {"Content-Type": "text/plain"});
    res.write("404 Not Found\n");

    function(err, file) {
     if(err) {
      res.writeHead(500, {"Content-Type": "text/plain"});
      res.write(err + "\n");
     res.writeHead(200, {"Content-Type": "text/html"});
     var str = ("" + file).replace("<!--%OUTPUT%-->", temp);

And outside the above function, the main routine, we have similar code as listed in 3, but insert the function call:

child = exec('./myi2c',
	    		function (error, stdout, stderr) {
				console.log('stdout:', stdout);
				console.log('stderr:', stderr);
				loadHTMLFile('/index.html', response, stdout);
				if(error != null) {
					console.log('exec error:', error);
  • Now we can update the temperature information on the website, both triggered by a button on the page, and by just automatically refreshing the temperature value whenever the temperature changes. Here is the simple client script for accomplishing this:
<script language="javascript">
<h1>Welcome to the world of Node.js</h1>

<p>Here is the demo of the weather station.</p>
<h2>Current temperature:</h2>
<span id="temperature output"><!--%OUTPUT%--></span>
<form action = "/test.js" method="post">
<input type="submit" value="get temperature">

5. Now we are trying to do something fancy! We want to send the user an automatic warning email when the temperature is too high. Here's the Javascript code using node.js mailer module. This code use SMTP server to send email to the destination.

var email = require('mailer');

email.SMTP = {
    host: '',
    port: 587,
    ssl: false,
    use_authentication: false,

    to : "",
    from : "",
    subject : "I love beagleboard!",
    body: "Hello beagle world.",

function(err, result) {
    if(err) {
  • However, the configuration on our beagle has some problem. The server has no response to mailer's request. We've tried telnet localhost 587, and connection can be connected. This means the 587 port is already opened. Then I tried the same code under my ubuntu system, it turns out everything works fine, the can receive the e-mail, except some client-side warning error when running the mail.js file. I think the reason it works on ubuntu is because when installing postfix, there's an automatic configuration step, which doesn't exist on our beagle installation. So there must be some problem with the postfix configuration of beagleboard. I've tried to copy all the configuration files under /etc/postfix to our beagleboard, but there's just the same problem. If I have more time, or someone else who's interested in continuing this project, I suggest you have some research on the configuration thing. Everytime you make some config changes, just run
postfix reload

to apply the change.

5. Our next goal is to toggle LED via web page, whose control flow structure is essentially similar to the i2c communications, plus, we have already learned the way to write to the led pin via nodejs script(see note1 above).

  • Before actually doing that, let's first organize our code in a more hierarchical and reasonable way.Thanks to Mr. Manuel Kiessling's excellent introductory tutorial "The Node Beginner Book", which gives a pretty decent explanation on how a formal web server architecture should be constructed using nodejs. Basically, we should maintain an index.js that starts all of our code, have a server.js to actually create the server and listen on the port for any posts from the client side, and pass the request and response to the router.js to handle different requests. In requestHandlers.js, each function then does the real work based on the request information and execute corresponding server responses.
  • The following is what's in index.js:
var server = require("./server");
var router = require("./router");
var requestHandlers = require("./requestHandlers");

var handle = {}
handle["/"] = requestHandlers.i2c;
handle["/led"] = requestHandlers.led;
handle["/i2c"] = requestHandlers.i2c;

server.start(router.route, handle);
  • And we abstract the server.js to be a general form so it is independent of what will actually be done at the server, such details is left for requestHandlers.js to accomplish:
var http = require("http");
var url = require("url");
var sys = require('sys'); 
var fs = require('fs');
var path = require('path');
var events = require('events');

function start(route, handle) {
	function onRequest(request, response){
      var pathname = url.parse(request.url).pathname;
      route(handle, pathname, response, request);

  console.log("Server has started.");

exports.start = start;
  • router.js gets the request's pathname and call different functions according to different request url:
function route(handle, pathname, response, request) {
  console.log("About to route a request for " + pathname);
  if (typeof handle[pathname] === 'function') {
    handle[pathname](response, request);
  } else {
    console.log("No request handler found for " + pathname);
    response.writeHead(404, {"Content-Type": "text/plain"});
    response.write("404 Not found");

exports.route = route;
  • In requestHandlers.js, we need two functions, one for handle i2c request, another for led toggling request:
function i2c(response, request) {
  var uri = url.parse(request.url).pathname;
  ...//same as described above, including calling loadHTMLFile function that's also in requestHandlers.js

function led(response, request) {
  ...//details in below

6. Now it's time for us to think about how to toggle LED via web page. Turns out it's very similar to how i2c works. However, this time we need to not only parse the uri of the request, but also get the posted data from the request, parse them and write them into the appropriate file system. The event-driven nodejs utilizes "addListener" function to achieve the task, with parameter "data" to receive the data and "end" to handle and process them. The data received(in type of string) should be converted to object class by the "querystring" module. On the client side, we use exclusive radio button to allow user to choose the toggle mode of LED:

<form action = "/led" method="post" size="30">
            <input type="radio" name="mode" value="nand-disk" >nand-disk
            <input type="radio" name="mode" value="mmc0" />mmc0
            <input type="radio" name="mode" value="heartbeat" >heartbeat
            <input type="radio" name="mode" value="none" >none
            <input type="submit" value="Select"  onclick="xmlhttpPost()">

The corresponding javascript just submits this form to /led, which then be handled by router to execute led() function:

function xmlhttpPost() {

The following is the server side function code in requestHandlers.js:

var qs = require('querystring');
var url = require('url');
var sys = require('sys');
var fs = require('fs');
var path = require('path');
function led(response, request) {
  var postData = "";
   var pathname = url.parse(request.url).pathname;
   console.log("Request for " + pathname + " received.");


    request.addListener("data", function(postDataChunk) {
      postData += postDataChunk;
      console.log("Received POST data chunk '"+
      postDataChunk + "'.");

    request.addListener("end", function() {
      var ledtype = qs.parse(postData);
          fs.writeFileSync("/sys/class/leds/beagleboard::usr0/trigger", ledtype.mode);

Another thing to notice is, in order for this requestHandler for led.js not to jump to a brand new web page but stay on the current one, the normal "request.end()" code, which indicates the completion of an intact .js page, should be left out.


Give some concluding thoughts about the project. Suggest some future additions that could make it even more interesting.