This is a brief introductory tutorial on how to work with the Raspberry Pi. If not mentioned otherwise, the material here is valid for all models of the Raspberry Pi. Some Raspberry Pi 3 specific topics will be marked as such.
Table of Contents
- Overview
- Setup the Operating System Image
- The RPi as a Regular Computer
- Remote Control -- The RPi as an Embedded Device
- Installing NodeJS
- A First JavaScript Program
- Some JavaScript Examples
- Making Use of the GPIO Pins
- Virtual Network Computing
- References
In contrast to a regular computer the Raspberry Pi (RPi) does not have a built-in hard drive or SSD. Therefore we need to provide the operating system (OS) and all persistent data as an image on an SD card. In the first four sections of this tutorial we will see how to build such an image, get the RPi running and connect it to a computer so we can control it.
Once we can access the RPi remotely, we will install NodeJS and write some JavaScript to verify that NodeJS is working correctly. This enables us to install raspio and johnny-five via npm to take control over the RPi's GPIO pins. Besides a classic LED-blinking tutorial, the hello world of embedded devices and some audio streaming, we will also turn towards some more specialized capabilities of the RPi 3 and send out HTTP(S) requests via WiFi.
ℹ️ For the study group we will provide SD cards with pre-built images that already contain the software stack for various tasks. If you are not planning to setup a RPi yourself, you can thus skip sections Setup the Operating System Image and The RPi as a Regular Computer and go straight to Connecting via SSH.
First, we will install the Raspbian operating system for the Raspberry Pi. You can download the zip file from here. The official Raspberry Pi homepage also provides an excellent installation guide for Linux, MacOS and Windows.
ℹ️ We will stick to the plain Raspbian OS officially supported by the foundation as opposed to others. While installing Raspbian as described above should not pose any problems, it might be even easier for beginners to start out with NOOBS (which contains Raspbian).
Now we should have a (micro) SD card with the Raspbian image that we can insert into the RPi's card slot and are ready to go. For the Raspberry Pi 3 you will need a micro SD card, all lower versions use a regular SD card. Of course, the RPi is worthless without some input and output capabilities. In the next two sections we will describe two ways to control the RPi. The first possibility is to operate the RPi more or less like a regular computer.
The RPi comes equipped with plentiful interfaces precisely for this mode of operation. For example, all models have an HDMI and at least one USB 2 port. Besides Model A(+) they actually have at least two of them. Simply connect a keyboard and a mouse via USB as well as a montior via HDMI before you connect the RPi to the power supply. As soon as you provide power via the micro USB port, the RPi will boot up. It can now be used just like a regular computer. The RPi will recognize most of the common keyboards and mice during the boot process. If you have worked on a Linux machine before, you can get to work right away, as Raspbian is based on Debian.
While this is a very convenient and intuitive way to interact with the RPi, it is not the approach we want to take here. Thus we are not going into more detail at this point. Typical use cases for the RPi do not involve it being hooked up to a monitor, keyboard and mouse all the time. We want it to operate as a standalone device, but still be able to control it remotely. Let us discuss this mode of operation in the next section.
❗ Make sure that the power supply delivers sufficient current for your model. Of course, the power requirements depend heavily on the model, the connected peripherals and the task. The official homepage recommends the following specifications
| Product | Recommended | Max. USB Draw | Bare-Board |
|---|---|---|---|
| Model A | 700mA | 500mA | 200mA |
| Model B | 1.2A | 500mA | 500mA |
| Model A+ | 700mA | 500mA | 180mA |
| Model B+ | 1.8A | 600mA/1.2A | 330mA |
| 2 Model B | 1.8A | 600mA/1.2A | |
| 3 Model B | 2.5A | 1.2A | ~400mA |
To communicate with the RPi remotely we first need a connection between our laptop and the Raspberry Pi. Throughout this tutorial we will refer to any normal computer one might use to control the RPi remotely as a laptop in order to make a clear distinction between the RPi (which is also kind of a computer) and the regular machine. This connection will be established via a Ethernet cable. In terms of network protocols perhaps the standard way to login on a machine remotely is ssh (Secure Shell).
ℹ️ During the study group the setup might slightly deviate from the one presented here. Most likely all RPis will be connected to a switch and you will access them via WiFi instead of a physical Ethernet connection. However, the procedure outlined below will be almost identical.
Many online tutorials on remote access of the RPi assume that the the RPi is already connected to the internet or that we know it's IP address in the local network, which apparently requires some configuration. If we start from scratch with an RPi that was never hooked up to a monitor and keyboard for prior configuration, we have to initialize all necessary settings right in the image on the SD card.
To this end put the SD card back into your laptop and navigate to the root directory. There is a file named cmdline.txt. Open this file in your favorite editor, it should read something like
dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait
Do not worry if it is not exactly the same. This file contains some commands that will be called during the root process of Raspbian. It thus allows us to perform configurations. Specifically we will assign a unique IP address to the RPi. Therefore, at the end of the last line in cmdline.txt add ip=169.254.0.XXX, where XXX is some positive integer number that should be unique in the network, in particular it should differ from the IP address of your laptop. The whole cmdline.txt should then read for example
dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait ip=169.254.0.2
❗ Be careful not the add or remove any empty lines in
cmdline.txt.
You can now eject the SD card and put it back into the RPi.
ℹ️ If you encounter any problems in this step, check out this tutorial for a more detailed description.
Before connecting the RPi to the laptop, make sure that you are using the Dynamic Host Configuration Protocol (DHCP), i.e., the laptop is automatically assigned an IP address for connections via the Ethernet port.
TODO
TODO
Open System Preferences and click on Network.
Then make sure Using DHCP is selected from the drop down menu.
Once this is set up and the SD card is back in the RPi's card slot, connect an Ethernet cable to both your laptop and the RPi's Ethernet port.
ℹ️ Many modern laptops do not have an Gigabit Ethernet port anymore. In this case you need to get an Ethernet to USB or Thunderbolt connector. Note again that we will setup remote access via WiFi during the study group so you are not required to bring such an adapter to the summer school.
Then connect the RPi to a power supply via the micro USB port. Now we have to wait a little bit for the RPi to boot. (The Ethernet port is hot-plugging capable, i.e., you can connect and disconnect it at any time and it should still work.)
The only platform independent indicator whether everything works correctly, is to try it out. Hence, our next step is to open up a terminal aka. console aka. shell and type
ping 169.254.0.XXXwhere XXX is to be replaced with the number you chose above. Ideally the output will look like the following screenshot.
You can abort the ping command just like any other command typically with CTRL + c. If the ping test does not work you should wait a couple seconds and try it again. Chances are the RPi has not yet booted and configured the network settings.
If even after multiple tries you see output like in the screenshot below, something went wrong. In that case we recommend checking your laptop's network settings (make sure DHCP is enabled) and carefully go through the instructions again.
Now that the RPi responded to our ping, we are confident that the connection can be established and we type
Remember to replace XXX with the chosen number. Upon request type in the password
raspberryand confirm with the Enter key.
❗ The default username of a fresh Raspbian installation is
piand the default password israspberry.
You should see a short legal disclaimer and the command line prompt should turn into pi@raspberrypi like in the screenshot below.
Now we have full control over the Raspberry Pi.
❗ In this section we assume that the Raspberry Pi has a working connection to the internet. Hence it applies to the Raspberry Pi 3 and/or previous models equipped with a functioning WiFi shield. During the study group you will receive images with NodeJS pre-installed so you can skip this section and continue with A First JavaScript Program.
NodeJS® is a JavaScript runtime built on Chrome's V8 JavaScript engine. JavaScript is one of the three core technologies for most of the content production on the internet and as such typically executed by browsers. NodeJS allows us to execute JavaScript code outside of a browser, for example from the command line.
On Raspbian we have access to the Linux' Advanced Package Manager (APT). Raspbian actually already comes with NodeJS installed, but it is quite an old version. You can check this by typing the following in the terminal while you are connected to the RPi
nodejs -vTo install a newer version, we first remove the old version and certain tools that depend or build on it, e.g., Node-Red and NPM. For the whole workflow enter all these commands one after the other. To avoid typos it is often easiest to just copy-paste the commands.
sudo apt-get remove nodered -y
sudo apt-get remove nodejs nodejs-legacy -y
sudo apt-get remove npm -y # in case npm has been installed previously
sudo curl -sL https://deb.nodesource.com/setup_5.x | sudo bash -
sudo apt-get install nodejs -yThis might tike a while. We can check whether the installation was successful with
nodejs -v
npm -vThe first command should output something like v5.11.1 (we only care about the 5 in the beginning) and the second should give something close to 3.8.6. You can also choose even newer versions of NodeJS by adjusting the link in the curl command above. For example, you could replace setup_5.x by setup_6.x. At the time of this writing the most current version of NodeJS is v6.3.1.
After all the preparation we can finally write our own JavaScript code and run it on the RPi. The classic hello world turns into a one-liner in JavaScript. Simply create a file, for example hello.js, containing only
console.log('Hello World');Let us run this program from the command line with
node hello.jsAs simple as that! We can now leverage the full power of JavaScript (EcmaScript 6) and NodeJS. If you are already familiar with JavaScript but have not used NodeJS, the documentation will certainly be a useful resource.
❗ For the first two examples in this section the Raspberry Pi needs to be connected to the internet. For the third example one only needs internet connection to install the necessary packages. (We will provide SD cards with images that already have the necessary packages installed.)
Let's do another more interesting example. In the CC3200 tutorial we have shown how to send a HTTP(S) request as well as receive the answer and analyze the results. What took quite some time and many lines of C(++) code can now be done effortlessly in fewer than ten self-explanatory lines:
var http = require('http');
http.get('http://httpbin.org/bytes/4', (req) => {
var str = '';
req.on('data', (chunk) => {str += chunk;});
req.on('end', () => {console.log(str);});
}).on('error', (e) => {console.log(`error: ${e.message}`);});Here we query httpbin.org for four random bytes. Therefore the output of this program should be 4 random symbols. Note that some bytes represent non-printable symbols.
While a HTTPS request required much more effort compared to HTTP on the CC3200 Launchpad, NodeJS now does all the heavy lifting for us. We can basically replace each occurrance of http with https in the code sample above. In the following example we query random.org for a uniformly distributed random integer from 1 to 100. We also output meta data about the request which gives us some insight into what is actually going on behind the scenes.
var https = require('https');
https.get('https://www.random.org/integers/?num=1&min=1&max=100&col=1&base=10&format=plain&rnd=new',
(req) => {
console.log('headers: ', req.headers);
var str = '';
req.on('data', (chunk) => {str += chunk;});
req.on('end', () => {console.log(str);});
}).on('error', (e) => {console.error(`error: ${e.message}`);});Finally, let's try to make use of the RPi's 3.5mm headphone jack. Before we can stream music to the headphone jack via JavaScript we need to install some packages.
❗ This step requires a working internet connection. (We will provide SD cards with images that already have the necessary packages installed.)
sudo apt-get install libasound2-dev
npm install --save speaker lameNext we need an audio file that we want to play. To this end open a fresh terminal on your laptop (no ssh connection to the RPi). Navigate to the directory with the desired audio file, e.g., megahit.mp3. We will use the save copy tool to copy the audio file to the Raspberry Pi:
scp megahit.mp3 [email protected]:/Music/Again, recall that XXX has to be replaced by the correct number you assigned to the RPi. For more information about the save copy command you can read its manpages man scp.
The JavaScript code itself is again pretty short and self-explanatory:
var fs = require('fs'); // we need access to the file system
var lame = require('lame'); // lame is an open source mp3 encoder
var Speaker = require('speaker'); // access to sound drivers/headphone jack
fs.createReadStream('/home/pi/Music/megahit.mp3')
.pipe(new lame.Decoder())
.on('format', function (format) {this.pipe(new Speaker(format));})
.on('error', (e) => {console.error(`error: ${e.message}`);});Everything we did so far, we could have run on any machine with NodeJS and the necessary packages installed. Now we want to actually use the RPi as an embedded device by accessing its GPIO pins.
First we need to install the necessary libraries. The raspi-io library handles the low level control of the GPIO pins while johnny-five allows for a simple high level workflow.
❗ This step requires a working internet connection. (We will provide SD cards with images that already have the necessary packages installed.)
npm install johnny-five raspi-ioWe have finally come to the point where we can write our first hello world of embedded devices, the blinking LED. We simply follow the official example at johnny-five.
var five = require("johnny-five");
var raspi = require("raspi-io");
var board = new five.Board({
io: new raspi()
});
board.on("ready", function() {
var led = new five.Led("P1-13");
led.blink();
});You can learn more about the pin naming and functions in the documentation of raspi-io (in particular also here) and in the examples section of the johnny-five homepage. A very basic description of GPIO pins in general can be found on the official Rapsberry Pi Homepage. From here on it is mostly a matter of reading documentations and tutorials as well as trial and error to create truly awesome embedded applications.
If at some point you feel that you really want to work with the graphical user interface of the Raspbian OS, but do not have a monitor, you can share the RPi's Desktop with your laptop via virtual network computing (VNC). This allows us to remotely control the desktop interface of the RPi. You'll see in a window on your laptop exactly what a monitor connected to the RPi would show. You can interact with the virtual desktop in the exact same way as if your laptop mouse/touchpad and keyboard where hooked up to the RPi.
We will use TightVNC.
❗ This step requires a working internet connection. (We will provide SD cards with images that already have the necessary packages installed.)
sudo apt-get install tightvncserverOnce the installation finished successfully, we can launch a virtual server
tightvncserverYou will be asked to enter a password and an optional view-only password. While anyone with the first password you enter can view and control the RPi remotely once the VNC server runs on the RPi, the second password only provides view rights. That is like looking over someone's shoulder while they are using a laptop. You can see everything that's going on, but you can't intervene. For this tutorial we will choose raspberry as a password both times.
Next we can start the VNC server. The vncserver command takes several options which are explained in detail in the manpages man vncserver. A typical launch command looks like
vncserver :1 -geometry 1920x1080 -depth 24The :1 specifies the so called display number. Note that the number :0 is reserved by default, thus we should use a number greater than 0 for our display. The -geometry options determines the resolution, here we are displaying the desktop in full HD. The -depth option specifies the color depth (must be between 8 and 32).
As already mentioned there is always an X session running on display :0 thus we have now two X sessions running. To save resources it is a good idea to shut down the display manager
service lightdm stopThe RPi is now ready. The VNC server is running and we can connect to it from our laptop. The connection process itself depends on the operating system on your laptop. Before we go into that, to quit the VNC server on the RPi simply type
vncserver -kill :1❗ When using the RPi via a VNC connection on your laptop, do not use the logout button in the menu bar of the desktop. Simply quit the screen sharing/remote desktop viewer application running on your laptop and subsequently kill the VNC server on the RPi as described above.
It is likely that your Linux distribution already ships with a remote desktop viewer. Just search for a Remote Desktop Viewer application in the menu bar. When asked for the address or hostname of the VNC server, enter 169.254.0.XXX:5901, where XXX needs to be replaced by the number you used for the IP address of the RPi. Depending on the application you might be required to use vnc://169.254.0.XXX:5901 instead. The weird number 5901 is explained at the end of this section. You will be asked for a password, which is the first one you entered when setting up the VNC server on the RPi. Then the desktop of the Raspberry should pop up in a new window.
If your distribution does not contain a remote desktop viewer, you can install TightVNC almost like we did on the RPi. Note that while we installed tightvncserver on the RPi we now just want a viewer. So on your laptop (not the RPi) type
sudo apt-get install xtightvncviewerTo connect to the running session on the RPi simply enter
vncviewer 169.254.0.XXX:5901Again, you might have to replace :5901 by :1 or :5501 as explained at the end of the section.
On Windows you can download a VNC viewer software (32 or 64 bit) from tightvnc.com. After installation, launch the TightVNC viewer from the start menu. You will be asked for an IP address or hostname of the VNC server you want to connect to. Enter 169.254.0.XXX::5901, where you need to replace XXX with the number you chose for the IP address of the RPi. If that is not working, instead of ::5901 also try :5901 or simply :1. The weird number 5901 is explained at the end of this section. Next, click Connect and you will be asked for a password, which is the first one you entered when setting up the VNC server on the RPi. Then the desktop of the Raspberry should pop up in a new window.
On MacOS you do not need any extra software. There is an inbuilt Screen Sharing app, which is located at System/Library/CoreServices/Application/Screen Sharing.app. You can also just search for Screen Sharing with Spotlight. When you launch the screen sharing app you will be asked to enter the hostname of the VNC server. Here we enter the IP address of the RPi followed by the number :5901, see image below. The weird number 5901 is explained at the end of this section. When you click on Connect you will be asked for a password, which is the first one you entered when setting up the VNC server on the RPi. Then the desktop of the Raspberry should pop up in a new window.
Alternatively to the Screen Sharing app, you can also just open Finder, click on Go in the menu bar at the very top of you desktop and then Connect to Server... (or simply press ⌘K). Then enter vnc://169.254.0.XXX:5901 (replace XXX by the number you chose in the RPi's IP address), like in this screenshot
Either way the desktop of the Raspberry should pop up in a window like the one below
ℹ️ The last digit
1in5901corresponds to the display number:1we specified on the RPi. The number5900is often used as the standard default port for VNC starting at 0. Hence to get to display:1, we add 1 to arrive at5901. If that does not work, you might also try just:1(the port is found automatically) or:5501(a different port that is sometimes used) instead of:5901.
ℹ️ If you want the RPi to launch a VNC server automatically on startup so that you can always connect with a VNC viewer right after it booted and for further information on setting up a VNC server on the RPi follow the instructions here.
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