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Learning Javascript Robotics
Learning Javascript Robotics

Learning Javascript Robotics: Design, build, and program your own remarkable robots with JavaScript and open source hardware

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Profile Icon Kassandra Perch
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$32.99
Paperback Nov 2015 160 pages 1st Edition
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Arrow left icon
Profile Icon Kassandra Perch
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$32.99
Paperback Nov 2015 160 pages 1st Edition
eBook
$17.99 $25.99
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Renews at $19.99p/m
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Learning Javascript Robotics

Chapter 2. Working with Johnny-Five

In this chapter, we'll begin working with Johnny-Five to build our own robotics projects. We'll cover what makes Johnny-Five a great library for starting with robotics, and we will build our first robot. We'll learn how we can manipulate this robot in real time from the command line—a feat not easily replicated on other platforms! By the end of this chapter, you'll have an open understanding of the software involved, which will serve as a great foundation for more complicated hardware builds.

This chapter will cover the following topics:

  • How a Johnny-Five program works
  • Understanding events in Johnny-Five
  • Wiring an LED and making it blink
  • Using Read-Eval-Print-Loop (REPL)

What you'll need for this chapter

All you'll need for this chapter is your microcontroller (the examples here still use an Arduino Uno) and a small handful of LEDs—we'll be wiring only one LED, but you may want a couple of spares, in case one burns out.

How a Johnny-Five program works

In this section, we'll take a look at the internals of a Johnny-Five program in more detail, so we can start building more complex applications.

Objects, functions, and events

Johnny-Five programs work using an event-based structure, and there are three concepts to keep in mind: objects, functions, and events.

Objects tend to programmatically represent our physical electronic components and are usually constructed using the new keyword. A few examples of objects in Johnny-Five include the five object, which represents the Johnny-Five library, the Board object, which represents our microcontroller; and the LED object, which will programmatically represent our LED:

var led = new five.Led(11);

Functions are available for the objects we create and usually represent the actions that our robots can do. For instance, the LED object has an on() and off() function that turns the LED on and off:

led.on();
led.off();
led.blink();
led.stop();

Events are fired on objects...

Understanding events in Johnny-Five

The events in Johnny-Five are a very important concept—this is also a new concept, especially if you are used to low-level language programming. It's very similar to the idea of interrupts, but definitely strays away from the traditional robotics programming paradigm of an event loop. While you can create timers and loops in Johnny-Five, it highly encourages an event-based programming approach, which can need some practice.

Why events?

A question that gets asked a lot is, "Why event-based? Why not loop-based and interrupt-based as in previous methods?".

A lot of this has to do with the way robots work and the way we think about how we program robots. When you think about what you want a robot to do, you're less likely to think "Every X seconds, I want to check for A and start task B..." and you are more likely to think "When Y happens, I want to start event C...".

The event-based system in Johnny-Five works really...

Wiring up an external LED

For our first hardware project, we're going to wire an LED to the Arduino. An LED, or a Light Emitting Diode, is a component that lights up when electric current is passed through it. They come in many colors and sizes and are one of the most easy-to-use and versatile components in hobbyist robotics.

Setting up the hardware

First, take an LED. We'll determine the positive and negative leads of the LED—for this component, it's straightforward: the positive lead is longer than the negative lead.

Setting up the hardware

Determining the positive and negative ends of an LED

To wire the LED to an Arduino, place the positive lead on pin 11 and the negative lead on the pin marked GND, just like in the following diagram:

Setting up the hardware

Wiring up our LED

You can also use a breadboard if you wish to—it will look like the following:

Setting up the hardware

Wiring an LED with a breadboard

Now that we've wired up the LED, we're going to make it blink as we did in the last chapter. The script looks very familiar...

Using the Read-Eval-Print-Loop (REPL)

The Read, Eval, Print Loop, or REPL, is a concept relative to many scripting languages, but it is new to libraries, and definitely new to robotics. Think about how you alter the state in a typical Arduino program: you modify the source code, re-load it onto the board, and wait for it to run.

However, due to the way Johnny-Five works, we can modify the state of our robot code while the code is running. This is because we use Firmata—the board is just a thin client that reacts to instructions from our node program, so if we let our Node programs send different instructions, we can change how our robot works in real time.

The way to do this in a Johnny-Five program is by injecting components into the REPL, which allows us to use them.

Making components available to the REPL

We're going to modify our script from the previous section in order to manipulate our LED. To do this, we're going to use the this.repl.inject() function. The this keyword...

What you'll need for this chapter


All you'll need for this chapter is your microcontroller (the examples here still use an Arduino Uno) and a small handful of LEDs—we'll be wiring only one LED, but you may want a couple of spares, in case one burns out.

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Description

There has been a rapid rise in the use of JavaScript in recent times in a variety of applications, and JavaScript robotics has seen a rise in popularity too. Johnny-Five is a framework that gives NodeBots a consistent API and platform across several hardware systems. This book walks you through basic robotics projects including the physical hardware builds and the JavaScript code for them. You'll delve into the concepts of Johnny-Five and JS robotics. You'll learn about various components such as Digital GPIO pins, PWM output pins, Sensors, servos, and motors to be used with Johnny-Five along with some advanced components such as I2C, and SPI. You will learn to connect your Johnny-Five robots to internet services and other NodeBots to form networks. By the end of this book, you will have explored the benefits of the Johnny-Five framework and the many devices it unlocks.

What you will learn

  • Familiarise yourself with JohnnyFive Read, Eval, and Print Loop (REPL) to modify and debug robotics code in real time
  • Build robots with basic output devices to create projects that light up, make noise, and more
  • Create projects with complex output devices, and employ the JohnnyFive API to simplify the use of components that require complex interfaces, such as I2C
  • Make use of sensors and input devices to allow your robotics projects to survey the world around them and accept input from users
  • Use the Sensor and Motor objects to make it much easier to move your robotics projects
  • Learn about the Animation API that will allow you to program complex movements using timing and key frames
  • Bring in other devices to your JohnnyFive projects, such as USB devices and remotes
  • Connect your JohnnyFive projects to external APIs and create your own Internet of Things!
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Table of Contents

10 Chapters
1. Getting Started with JS Robotics Chevron down icon Chevron up icon
2. Working with Johnny-Five Chevron down icon Chevron up icon
3. Using Digital and PWM Output Pins Chevron down icon Chevron up icon
4. Using Specialized Output Devices Chevron down icon Chevron up icon
5. Using Input Devices and Sensors Chevron down icon Chevron up icon
6. Moving Your Bot Chevron down icon Chevron up icon
7. Advanced Movement with the Animation Library Chevron down icon Chevron up icon
8. Advanced Components – SPI, I2C, and Other Devices Chevron down icon Chevron up icon
9. Connecting NodeBots to the World, and Where to Go Next Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon
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