Arduino meets JavaScript (Part one)

Understand a bit about firmata and Johnny-Five library

Weeks ago I got a nice insight:

A Javascript library that would connect Arduino boards by serial port and send specific hardware commands. Leaving all the heavy processing to the computer itself, using the board just as an I/0 device for physical interactions.

Well, happens to be a nice insight, I actually did get enthusiastic about it, and I started to code right away! But, also happens that someone already got the idea before me, and coded on an hackathon, published at GitHub/npm as johnny-five, and it’s actually very very nice.

You still can check my project at GitHub, I’m going to code the idea, now based on firmdata, just for fun. :)

About Johnny-Five

Johnny-Five is an Open Source, Firmata Protocol-based, IoT and Robotics programming framework developed at Bocoup. Johnny-Five programs can be written for Arduino (all models), Electric Imp, Beagle Bone, Intel Galileo & Edison, Linino One, Pinoccio, Raspberry Pi, Spark Core, TI Launchpad and more!

The name is a reference to the Short Circuit 80’s movie.

How does it work?

First of all let us understand some concepts:

Classic Process

Usually to make an Arduino do something, you:

  • code
  • compile
  • burn into the board
  • test

Once the code is done, you compile it to a hex file, which contains the specific bytes that need to be written to the program the memory of the chip on the Arduino board. This file is then uploaded to the board: transmitted over the USB or serial connection via the bootloader already on the chip or with external programming hardware.

After the code is “uploaded” into the chip, you have, most of the times, a stand-alone system, which means that it doesn’t require the computer to work so you can unplug the USB port, connect it to a power source, and it will run forever.

If by any chance you need to make changes to your code, you MUST make the whole process all over again.


Every Arduino Board has a specific Flash storage size, that limits your code size to be around 30k, or 200k depending on the board type.

It also has a very interesting memory limitation, specified on the datasheet, the program memory supports at least 100,000 cycles, so it means that, you do have a limit of times that you can repeat the code uploading process, it’s a very huge amount, but not endless.

Anyway, check this and this.

New Process

The “new process” is based on the firmdata protocol, let us see how does it work.


Firmata is a generic protocol for communicating with microcontrollers from software on a host computer. It is intended to work with any host computer software package.

Let us get a better picture of this through an example:


Imagine yourself coding a system that allows the user to hook up to 30 lamps into arduino ports and turn then on and off by the computer, on a cloud server, from anywhere in the world.

Let say your firmware, on the arduino consists on an API client that requires every X seconds a URL of your cloud server, and retrieve a JSON file with all the pins and if they should be on or off.

That’s nice, pretty neat, but now imagine that you want to make improvements, so now, people could hook up PWM devices, to read data from all sort of sensors, like temperature, and then they can create rules like, if the room temperature is >= 30 degrees celsius, turn the air-conditioner on, and this kind automated tasks.

  • What would do to mantain legacy hardware/software?
  • Would you ask to your 10.000 customers to upload new code on their boards? Will you do that?
  • If in the future you need to create plans, where the user needs to pay $10,00 for 10 rules, $20,00 for 30 rules, $30,00 for 50 rules, how would you implement that without compromise the current hardware/software? (imagine that your current hardware already supports those specifications).

It’s getting hard now, isn’t ?


What if, you could, instead of sending JSON file with just “pins” and leaving the process to arduino, make the heavy process on the server and just send to arduino “low-level” I/O commands ? Would that solve your problems ?

Yeap! With firmata, you actually CAN do that, so your board would request the API url and wait for commands, like digitalWrite, analogWrite. This way you would not need to worry about anything related to the firmware on your board, legacy code, …

Johnny-Five library uses the firmata to provide a very nice way to code with arduino + nodejs.


This way, your arduino will become a “zombie”, it will depend on the computer to work, because all the logic depends on the computer. As the example says, you can also transmit the commands by network packages.


After this theoretical first part, let’s get more practical.

I assume that you already installed, Arduino IDE and NodeJS, and that you know a little bit about those two.

Arduino Setup

Start the Arduino IDE, Go to the “File” menu, and under “Examples” you should see a “Firmata” menu. Choose “StandardFirmata” from this menu. This will open the Arduino sketch for the StandardFirmata protocol.

Upload the code, and close the Arduino IDE.

Let’s code

Now jumping to the code, let’s create a new folder, anywhere on your computer, init a node-package, and run:

$ npm install johnny-five --save

Let’s create a small example, based on the arduno blinking led hello world, with this new process, it will be something like:

var Arduino = require('johnny-five');
var board = new Arduino.Board();
var LEDPIN = 13;
var OUTPUT = 1;
board.on("ready", function(){
var val = 0;
this.pinMode(LEDPIN, OUTPUT);
this.loop(100, function() {
this.digitalWrite(LEDPIN, (val = val ? 0 : 1));

To run it, just:

node index.js

The code, basically defines the board, get the ready event, sets the pinMode of the led, as an output, creates a loop that runs every 100 ms and toggles the led state.

J5 will search automatically for boards connected by USB/Serial.

Now, checkout the same example, taking vantage of the internal libraries codes:

var Arduino = require('johnny-five');
var board = new Arduino.Board();
var led = new Arduini.Led(13);
board.on("ready", function(){

On the second code-snippet, we don’t set the pinMode, noticed? Well, that’s because when we create the instance of the Led, the constructor inside the led class does that for us.

Checkout the here code inside the Led class that sets the pinMode, lines 94 to 105.

We also use the strobe method, that toggles the led on a pre-determined interval, you can also check the code here


I hope you enjoyed the reading, please comment below if you did. Suggestions for the part two are also welcome.


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