{"id":2888,"date":"2014-10-03T17:59:33","date_gmt":"2014-10-03T21:59:33","guid":{"rendered":"https:\/\/itp.nyu.edu\/physcomp\/?page_id=2888"},"modified":"2021-07-26T15:44:46","modified_gmt":"2021-07-26T19:44:46","slug":"lab-serial-communication-with-node-js","status":"publish","type":"page","link":"https:\/\/itp.nyu.edu\/physcomp\/labs\/labs-serial-communication\/lab-serial-communication-with-node-js\/","title":{"rendered":"Lab: Serial Communication with Node.js"},"content":{"rendered":"\n

<\/span>Introduction<\/span><\/h2>\n\n\n\n

You can write programs that handle serial communication in many different languages. This page introduces how to do it using node.js. Node is a JavaScript environment that allows user to write web server programs. Below, you’ll use it to connect a microcontroller to a web browser using the node.js programming environment, HTML, and JavaScript.<\/p>\n\n\n\n

To get the most out of this tutorial, you should know what a microcontroller is <\/a>and how to program a microcontroller<\/a>. You should also understand asynchronous serial communication<\/a> between microcontrollers and personal computers. You should also understand the basics of command line interfaces<\/a>.<\/p>\n\n\n\n

You will struggle with this tutorial if you aren’t familiar with JavaScript.  For more on JavaScript, see Douglas Crockford’s JavaScript: The Good Parts,<\/a> Manuel Kiessling’s  the Node Beginner Book<\/a>, or Shelley Powers’ Learning Node<\/a>.<\/p>\n\n\n\n

The current version of this tutorial works with version 6.x.x of the node-serialport library.<\/p>\n\n\n\n

This node.js introductory video<\/a> will help in understanding this lab. The code in the video is different than this lab, but the basic concepts are similar. This lab simplifies the process a bit.<\/p>\n\n\n\n

<\/span>Node.js<\/span><\/h2>\n\n\n\n

The JavaScript programming language is mainly used to add interactivity to web pages. All modern browsers include a JavaScript interpreter, which allows the browser to run JavaScript code that’s embedded in a web page. Google’s JavaScript engine is called v8<\/a>, and it’s available under an open source license. Node.js<\/a> wraps the v8 engine up in an application programming interface that can run on personal computers and servers. On your personal computer, you run it through the command line interface.<\/p>\n\n\n\n

Node was originally designed as a tool for writing server programs, but it can do much more. It has a library management system called node package manager<\/strong> or npm<\/strong><\/a> that allows you to extend its functionality in many directions. There is also an online registry of node libraries, npmjs.org<\/a>. You can download libraries from this registry directly using npm. Below you’ll see npm used to add both serial communication functionality and a simple server programming library to node.<\/p>\n\n\n\n

To get started, download the node.js installer<\/a> and install it on your computer. Then open your command line terminal. On OSX, open the Terminal app, which can be found in the Applications\/Utilities directory. On Windows, go to the start menu and type cmd then press enter to open a window to the command line.<\/p>\n\n\n\n

If you’ve never used a command line interface, check out this tutorial on the Unix\/Linux command line interface<\/a>.  From here on out, you’ll see the command prompt indicated like this:<\/p>\n\n\n\n

yourname@yourcomputer ~ $<\/pre>\n\n\n\n
 Any commands you need to type will follow the $ symbol. The actual command prompt will vary depending on your operating system. On Windows, it’s typically this: ><\/code>. On most Unix and Linux systems, including OSX, it’s $<\/code> or %<\/code>.<\/p>\n\n\n\n
When you’ve installed node.js, type this command at the command prompt to get the version of node that you’re running:<\/p>\n\n\n\n
$ node -v<\/pre>\n\n\n\n
 If you installed it correctly, you’ll get a version number like 12.18.0. The node installer should also install the node package manager (npm). You can check that in the same way:<\/p>\n\n\n\n
$ npm -v<\/pre>\n\n\n\n
Once node and npm are in place, you’re ready to create a new project. \n\n<\/a><\/p>\n\n\n\n
Related video: Install the serialport Node module<\/a><\/p>\n\n\n\n
<\/span>Hello from Node.js<\/span><\/h2>\n\n\n\n
There’s a library for node.js that allows you to communicate over your computer’s serial ports called serialport. If your computer’s connected to the internet, you can download install it automatically using npm. Create a new directory for your project:<\/p>\n\n\n\n
$ mkdir nodeSerialExample<\/pre>\n\n\n\n
Then change directories to that directory:<\/p>\n\n\n\n
$ cd nodeSerialExample<\/pre>\n\n\n\n

Now make a new text file in that directory with the name index.js<\/code>.<\/p>\n\n\n\n
This will be your main program file.  Add the following text to the file:<\/p>\n\n\n
\nconsole.log(\"Hello, and welcome to node.\");\n<\/pre><\/div>\n\n\n
Save the file, then run it by typing the following on the command line:<\/p>\n\n\n\n
$ node index.js<\/pre>\n\n\n\n
Your program should print out:<\/p>\n\n\n\n
Hello, and welcome to node.<\/pre>\n\n\n\n
The program will finish and return to the command line when it’s done. Seeing that script running is indication that node.js is fully working on your machine.<\/p>\n\n\n\n
You can also pass information into your node program using the process arguments on the command line.  Change your program like so:<\/p>\n\n\n
\nvar name = process.argv[2];\nconsole.log(\"Hello, and welcome to node,\" + name);\n<\/pre><\/div>\n\n\n
Run this as you did before, but add your name after the name of your program when you invoke it, like so:<\/p>\n\n\n\n
$ node index.js Tom<\/pre>\n\n\n\n
You’ll get the following:<\/p>\n\n\n\n
Hello, and welcome to node, Tom<\/pre>\n\n\n\n
The command line arguments are passed to your program as an array. The name was the third word you typed, or array element 2 (counting “node” as element 0 and “index.js” as element 1).  This is a useful technique, and you’ll see it later to pass the program your serial port’s name.<\/p>\n\n\n\n
<\/span>The Node Serialport Library<\/span><\/h2>\n\n\n\n
You’ll also need the node serialport <\/a>library, which you can install from the npm registry like so:<\/p>\n\n\n\n
$ npm install serialport<\/pre>\n\n\n\n
This command will make a new subdirectory called node_modules, and in that directory it will install all the necessary assets for the serialport library.  You’ll see a lot of text go by, and hopefully no errors. If you get errors, consult npmjs.org and the github wiki for serialport<\/a>. Now you’re ready to use the serialport library.<\/p>\n\n\n\n
The first thing you’ll want is a list of the serial ports. Replace the text of your program file with the following:<\/p>\n\n\n
\nlet serialport = require('serialport');\n\n\/\/ list serial ports:\nserialport.list().then (\n  ports => ports.forEach(port =>console.log(port.path)),\n  err => console.log(err)\n)\n<\/pre><\/div>\n\n\n
<\/span>Note: What’s With This Crazy Syntax?<\/span><\/h3>\n\n\n\n
If you’re new to JavaScript, this syntax may be confusing. Node.js examples tend to use anonymous functions<\/strong> frequently. JavaScript can pass functions as variables (and vice versa). \u00a0This is also using the JavaScript ES6 arrow function notation<\/a>. That’s what’s going on here.<\/p>\n\n\n\n
Stoyan Stefanov’s JavaScript Patterns<\/a> is useful for understanding the various patterns of JavaScript coding.<\/p>\n\n\n\n
When you run this script, you’ll get a list of your serial ports like so:<\/p>\n\n\n\n
$ node ListPorts.js\n\/dev\/cu.Bluetooth-Incoming-Port\n\/dev\/cu.Bluetooth-Modem\n\/dev\/cu.usbmodem1411<\/pre>\n\n\n\n
If you’ve got an Arduino plugged in via USB, you should see the name of your board’s port there as well. In the example above, which was run on OSX, the Arduino’s port is \/dev\/cu.usbmodem1411<\/code>.<\/p>\n\n\n\n
The process of using the serialport library will be the same every time:<\/p>\n\n\n\n