Hands-On Robotics with JavaScript

Microcontroller is a term that encapsulates a bunch of devices. It's a term used to describe a device that contains a processor, memory, and input/output peripherals (or ways to interact with those peripherals) that is meant for a particular type of task. One extremely common microcontroller is the Arduino Uno, and the Raspberry Pi technically falls into this category as well.

Microcontrollers interface with devices such as sensors, LEDs, and buttons using electrical signals that are sent and received through pins designed for input and/or output signals. These pins can be broken into multiple subcategories, as we'll find out in subsequent chapters, but you can address them as GPIO pins as a whole. We'll use that abbreviation throughout the book.

Debian is a distribution of Linux that is considered extremely user friendly for those new to using Linux. It contains many utilities that are commonly used while working with Linux preinstalled, and is compatible with a lot of the peripherals that you would use with a computer, such as Wi-Fi cards and USB devices.

Raspbian is a modified version of Debian specifically designed to run on Raspberry Pi devices. There are drivers for the GPIO pins, USB Wi-Fi devices, and expansion slots on the Pi that allow you to attach a specific display and camera. 

There are two flavors of Raspbian—Raspbian Full and Raspbian Lite. Full has a graphical desktop with programs aimed at educational programming and development. Lite (which we will be using for the projects in this book) only has a command-line interface, but still has full functionality when it comes to Raspberry Pi peripherals. As of the time of writing, the current version of Raspbian is 4.14, nicknamed Stretch.

Back in 2012, Rick Waldron wrote a node-serialport program to operate an Arduino Uno with Node.js, and formed a library around it called Johnny-Five. Since then, the Johnny-Five library has grown to over 100 contributors, and can control over 40 platforms, including the Raspberry Pi! It can also control many kinds of sensors and peripherals that you can use to create the robotics project you've been dreaming of in Node.js!

One of the ways the Johnny-Five library has grown to support so many platforms is by creating what are called IO plugins. You create an IO plugin for each type of board you wish to control. For example, we will be installing and using the Raspi-IO plugin to use Johnny-Five with the Raspberry Pi.

What is great about this system is that the code you write in this book can be used on any other platform that Johnny-Five supports (you just need to change PIN numbers)! Writing code for Node.js botnets is much easier when you're using the same APIs for any devices you might use.

Let's get back to the question of what the Raspberry Pi is. In short, it is a microcontroller. It has dozens of GPIO pins and can be used to interface with many physical peripherals in order to achieve specialized tasks. The low cost and small size allows the Raspberry Pi to be a versatile device, but the power involved allows you to use it for tasks that other microcontrollers may not pack the punch for.

An interesting fact about the Raspberry Pi is that, while it is a microcontroller, it can also be used as a fully fledged computer! While it certainly isn't the most powerful hardware, with full Raspbian installed, a Raspberry Pi attached to a monitor, keyboard, and mouse creates a great machine for kids and adults to learn programming on! The original intent of the Raspberry Pi was to create a low-cost educational machine to teach programming, and it exceeded every expectation in that regard. The fact that it's also a great microcontroller for the world of makers is a great bonus!

The projects we will build will take advantage of the fact that the Raspberry Pi is both a microcontroller and a computer. We'll use the Linux operating system, via the Raspbian distribution, and leverage it to run our projects in Node.js. We'll also use Johnny-Five and Raspi-IO to leverage the GPIO of the Raspberry Pi in order to create robotics projects in a way that makes the code easy to understand and portable to many different hardware platforms.

In the past, when you thought of robotics projects, it meant writing in C or C++, usually through the Arduino IDE and APIs. However, as microcontrollers have gotten more powerful, they are capable of running other programming languages, even scripting languages, such as subsets of Python and JavaScript.

And, of course, with computer/microcontroller hybrids, such as the Raspberry Pi, you're able to run stock Node.js, allowing you to create even advanced robotics projects without having to deal with any low-level languages. There are quite a few benefits to being able to code robotics projects in Node.js:

The following steps will show you how to download Raspbian Lite:

A screenshot of the Raspbian download page, with both Full and Lite download links

Luckily, the tools for burning OS images to SD cards have evolved arcane command-line tools that can overwrite your computer's hard drive as easily as it can the SD card. My current favorite is called Etcher, and it can be downloaded for any platform at https://etcher.io/, as shown in the following steps:

A screenshot of the Etcher program running on a Mac

A few minutes will pass as Etcher burns the image to your micro SD card, then verifies that it is present on the card. Once this is done, remove and reinsert the micro SD card so that your computer recognizes it as a drive again; the drive should be namedboot. We're not quite done editing the image files yet, so Etcher's polite attempt to eject the micro SD card drive needs to be ignored.

We need to edit and create some files on our Raspberry Pi's image in order to be able to access it with SSH when we turn on the Raspberry Pi. First, we'll set up the Wi-Fi using the following steps:

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
network={
    ssid="yourNetworkSSID"
    psk="yourNetworkPasswd"
}

A list of files on the micro SD drive, once I've made my edits

Once this is all done, fully eject the microSD drive, take the microSD card and insert it into the Raspberry Pi. We're now ready to boot up the Raspberry Pi and start installing software.

Once the micro SD card is inserted, plug your power source into your Raspberry Pi. A red and green LED should light up. The red LED should be solid—this is the power indicator. The green light will flicker on and off—this is the LED that indicates activity. The Raspberry Pi should take a maximum of a minute or so to boot up once you've plugged it in. Next, we'll SSH in. 

SSHing from a Linux or Mac

If you're on a Mac or Linux machine, you'll open up a Terminal and type the following:

ssh pi@raspberrypi.local

If you're successful, you'll see a question appear, asking about the authenticity of the host. Respond by typing yes and hitting Enter. You'll then be asked for a password, which is raspberry, as shown in the following screenshot: 

Successful SSH into a Raspberry Pi from a Mac Terminal

Once you've entered the password, you should see the following:

Successful login to a Raspberry Pi via SSH from a Mac

SSHing from Windows

In order to SSH from a Windows machine, you'll need to use a program called PuTTY. You can get it on https://putty.org/. But first, you'll want your Raspberry Pi's IP address. You'll need a monitor, an HDMI cable, and a USB keyboard. Once you have these, go through the following steps:

1. Plug the monitor, HDMI cable, and USB keyboard into the Raspberry Pi before booting it up. Then plug in the power supply.
2. When it prompts you for a username, type pi. When it asks for a password, enter raspberry. Once you are logged in, type ifconfig. You should see a lot of information appear.
3. Look for the wlan0 section and the inet address under that heading. For the following output, the IP is 192.168.1.106, as shown in the following screenshot. Write this IP down. Then, you can unplug the display and the keyboard—you won't need them again:

Getting the IP address from the Terminal

4. Once you have the IP address for your Raspberry Pi, you can boot up PuTTY. The window that opens is the configuration window, as shown in the following screenshot: 

The PuTTY configuration window

5. Type the IP address that you obtained into the field labeled Host Name (or IP address) and click the Open button. You'll be asked about the authenticity of the host (only the first time you connect). Select Yes. Then enter Pi as the username and raspberry as the password when prompted. Once that's done, you should see the following:

Successful login to the Raspberry Pi with PuTTY

Now that everyone's logged in, let's set up our Raspberry Pi for our projects!

When you log in, your Raspberry Pi will warn you that having SSH enabled with the default username and password isn't very secure, and it's absolutely right! The first step is to change our password.

In order to do so, in your SSH window, type in passwd and hit Enter. You'll be prompted for your current password (raspberry) and a new password. Type in whatever you like (just don't forget it)! You'll be asked to confirm it, and voila! The new password is set, as shown in the following screenshot. Your Raspberry Pi will be much more secure:

Changing your Pi password

Next, you'll make sure that the Raspberry Pi is updated and ready to go by running the following command:

sudo apt-get update && sudo apt-get upgrade

This will take a while, but it's worth it to make sure everything is properly updated.

Next, we'll set up the Raspberry Pi so that our hardware code can run. Run the following command:

sudo raspi-config

You'll be greeted with a graphical menu with lots of different options, as shown in the following screenshot:

The raspi-config menu

You'll want to use the arrow keys to select Interfacing Options, and then select I2C and Yes to turn it on. Repeat for SPI, then use Tab to close the menu. When it prompts you to reboot, say Yes, then SSH back in, because you're ready to install Node.js, Johnny-Five, and Raspi-IO!

In days past, you would have to compile the Node.js source on your Pi, to varying degrees of success because of the nonexistence of binaries for the ARM processor that Raspberry Pi uses. Luckily now, because of a rousing amount of third-party support in the past few years, you can easily download the binary from the https://nodejs.org/en/ website! But how are we going to do this from the command line of our Raspberry Pi? 

Detecting your version of ARM processor

If you're using the Raspberry Pi 3 Model B recommended by this book, you're most likely on ARM v8 (the Raspberry Pi 3 original is ARMv7, which is fine too!). But you should always double-check (doubly so if you're using a different Raspberry Pi, such as the Pi Zero or Pi 2/1 series). To check the ARM version on your Raspberry Pi, run the following in your SSH Terminal:

uname -m

You'll see a return message that looks like armv#, where # is a number (possibly followed by a letter). That number is what is important, because that number tells us which Node.js binary we will need. Once you have your ARM version, go through the following steps:

1. Head to the Node.js download page at https://nodejs.org/en/download/, as shown in the following screenshot:

A snapshot of the Node.js binary download page

2. Right-click on the ARM version link you need and copy the URL. Then, run the following in your Raspberry Pi's SSH Terminal:

wget <binary-download-url>

 

 

 

 

Replace <binary-download-url> (carats, too!) with the URL you copied from the Node.js download website. Once it's downloaded, we need to extract the archive using the following code:

tar -xvf node-v****-linux-armv**.tar.xz

3. The asterisks will differ depending on the current LTS version of Node.js and your ARM version. The Raspberry Pi will spit out a lot of filenames to the console, then give you back your shell prompt. This means that the binaries have been extracted into your home folder. We need to place them into the /usr/local folder. To do that, run the following:

cd node-v****-linux-armv** 
sudo mv ./lib/* /usr/local/lib
sudo mv ./share/* /usr/local/share

4. This will move all of the precompiled binaries to their new homes on your Raspberry Pi. Once this is done, run the following:

node -v
npm -v

You should see something like the following:

Successful Node.js installation results

5. If that's all well and good, you now have Node.js and npm installed! Let's wrap this up with Johnny-Five and Raspi-IO! Note that you can absolutely clean up the binary downloads by running the following:

cd ~
rm -rf node-v**-linux-armv**
rm -rf node-v****-linux-armv**.tar.xz

 

 

 

 

 

 

Note

Some of you with more Debian experience may be asking, well, why can't we just useapt-get? The short answer is that the package with the name node was taken a very long time ago, and because that is the case, and because sudo apt-get install nodejs is outdated (at the time of writing, using this command will install v4 when we needv8+, if it installs Node.js at all), we need to download the binaries and move them ourselves.

To install Johnny-Five, once you've made sure Node.js and npm are installed, run the following command:

npm i -g johnny-five raspi-io

This installs the libraries globally; you won't have to reinstall it every new project. And that's it! You're ready to start developing Node.js robotics projects on the Raspberry Pi with Johnny-Five!