Controlling an Arduino from Node.js

Posted Friday, March 02, 2012

After expressing an interested in learning microcontroller programming, a friend of mine purchased for me an Arduino Duemilanove, which arrived yesterday. Being someone who enjoys web programming, I of course wasted no time in figuring out how I could get it connected to a web page. I opted to use Node.js for my integration.

To communicate with the microcontroller, I used node-serialport, which allows you to make a connection to a serial port for reading and writing. For this test, I wrote a sketch to turn the onboard LED on pin 13 off when a 0 is read from the serial connection, and to turn the LED on when a 1 is read. The contents of this sketch follows; just upload it to your Arduino.

const int outputPin = 13; void setup() { pinMode(outputPin, OUTPUT); Serial.begin(9600); } void loop() { if (Serial.available() > 0) { int incomingByte = Serial.read(); if (incomingByte == 0x01) { digitalWrite(outputPin, HIGH); } else if (incomingByte == 0x00) { digitalWrite(outputPin, LOW); } } }View Gist for 00-sketch.c on GitHub

Next up, we need to send a 0 or 1 byte to the Arduino from Node; here’s a short CoffeeScript program that will blink the LED every second (I’ve hardcoded the device where my Arduino lives; substitute your own).

{SerialPort} = require('serialport') fs = require 'fs' port = '/dev/tty.usbserial-A600enDA' serial = null value = 0x00 toggle = => value = if value == 0x00 then 0x01 else 0x00 serial.write new Buffer([value]) console.log "Starting..." fs.stat port, (err, stats) -> if err? console.log "Couldn't stat #{port}" process.exit() console.log "Started." serial = new SerialPort port, baudrate: 9600 setInterval toggle, 1000View Gist for 01-blink.coffee on GitHub

From here, it’s not difficult to adapt this example into a more complete sample including a web server. Here’s a complete listing of my program, including a web page to access at the root URL to control the LED using jQuery Ajax requests.

{SerialPort} = require('serialport') fs = require 'fs' port = '/dev/tty.usbserial-A600enDA' express = require 'express' serial = null interval = null lightOn = false turnOn = => lightOn = true serial.write new Buffer([0x01]) turnOff = => lightOn = false serial.write new Buffer([0x00]) toggle = => if lightOn turnOff() else turnOn() app = express.createServer() app.get '/', (req, res) -> res.sendfile 'index.htm' app.get '/on', (req, res) -> clearInterval interval turnOn() res.end() app.get '/off', (req, res) -> clearInterval interval turnOff() res.end() app.get '/blink', (req, res) -> clearInterval interval interval = setInterval toggle, 500 res.end() console.log "Starting..." fs.stat port, (err, stats) -> if err? console.log "Couldn't stat #{port}" process.exit() console.log "Started." serial = new SerialPort port, baudrate: 9600 app.listen(8080)View Gist for 02-server.coffee on GitHub

<html> <head> <title>Online Lightswitch</title> <script src="http://cdnjs.cloudflare.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script> <script> $(function() { $("#on").click(function() { $.ajax('/on'); }); $("#off").click(function() { $.ajax('/off'); }); $("#blink").click(function() { $.ajax('/blink'); }); }); </script> <style> button { font-size: 20pt; } </style> </head> <body> <button id="on">On!</button> <button id="off">Off!</button> <button id="blink">Blink!</button> </body> </html>View Gist for 03-index.htm on GitHub

Start the server and visit http://localhost:8080 and click the buttons to control the lights!

Michelle Tilley

From the mind of a geek

Controlling an Arduino from Node.js

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