Introduction to Pi’s (Raspberry Pi)

The family of Raspberry Pi’s are just really small computers. You can plug a monitor, keyboard, and mouse into one and it will not look too different from your desktop. They are small and cheap, but what makes them really useful is that they have little slots (called GPIO’s) that you can stick wires into that allow you to build circuits that can get information from sensors and control devices like LED lights or motors.

This is a quick introduction about how to set one up. You’ll find lots of great tutorials on the internet. This one is specific to my needs: it’s an introduction to the Pi’s for students who are new to them; I’m setting it up with a web server so we can control the devices through a webpage; and I’m setting it up so you can control the Pi “headlessly”, which means you don’t need the keyboard, mouse, etc..

Installing the Operating System

Downloading the OS

Download: The operating system files can be downloaded from the Raspberry Pi website. We’re going to use the Raspbian Desktop version with the recommended software.

Your typical computer has a built in hard drive that stores the data you save, the programs/apps you install, and the operating system (OS) that runs it all. When you start the computer the first thing it does is read the files that make up the operating system from the hard drive and set them up in the active, processing memory (RAM). Then when you interact with the computer (type on the keyboard, click the mouse etc.) you’re interacting with the operating system: you tell the operating system what to do, like start up a web browser (Firefox, Chrome, Safari, Explorer, Opera etc.), and it does it. And when your apps want to do something, like save a file, they have to ask the operating system to do it.

On the Raspberry Pi the data for the operating system is not stored on a built in hard drive, but on an SD card (or microSD), which means that you’re going to have to install the operating system yourself to get your Pi running. You can find the operating system at the Raspberry Pi website’s download page.

Installing

As of this writing, I’ve been using balenaEtcher to install the operating system on the SD Card.

balenaEtcher is free and pretty easy to use. Hopefully, your computer has an SD card port, if not you’re going to have to find an adapter. Just plug your SD card into your computer and run Etcher, it will ask you to:

  • Select Image: Which is the Raspbian file you downloaded
  • Select Drive: Which should default to the SD card you plugged in (check the size of the drive to make sure)
  • Flash: Which writes the Operating System files to the SD card, making sure everything is in the right place.

You may see some warnings pop up about Unrecognized Files Systems or similar. You can just close those windows.

When the flashing is done, don’t take the SD card out of your computer (or put it back in if you have) just quite yet. We’re going to set it up so the Pi can automatically connect to the WiFi, which will make it easier to talk to.

Setting Up WiFi

You’re going to have to edit some files on the SD card to give the Pi the information about the WiFi situation so that it can automatically connect. This is most useful if you’re not going to plug in a keyboard and monitor and just want to control the Pi from your computer (more on how to do this later). If you do want to go the keyboard and mouse route, you can just plug the SD card into the Pi, power it up, and set up the WiFi like you would normally do on your laptop.

To edit the files I use Atom on Windows or TextEdit which is built in on Mac. These programs should allow you to easily save files as plain text, without any of the fancy styling that will create errors when the Pi operating system tries to get the information from the files.

WiFi

Create a new file called: “wpa_supplicant.conf” (based on these notes) containing:

ctrl_interface=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
 ssid="networkID"
 psk="password"
}

But you have to change:

  • networkID to the name of the WiFi network you’re trying to connect to
  • password to the password for the network

If you need to connect to multiple networks (home and school for example) you can add another network command on a new line after the first one:


network={
 ssid="otherNetwork"
 psk="otherPassword"
}

Save this file to the boot directory of the SD card.

ssh

ssh allows you to remotely connect to your Pi’s operating system. This means that you can use your laptop to control the Pi (however you’ll be using command line commands).

Create an empty file named “ssh” and save it to the boot directory of your SD card.

USB connection

You should be able to find your Pi on the network (I use an app on my phone called Fing) and ssh in. However, to do most of the setup, especially if the Pi has trouble connecting to the WiFi (or you can’t find it on the network), you’ll probably want to set up your pi so you can plug it into your computer’s USB port and control it from the computer. Based on the notes from Adafruit, do this:

Open the file “config.txt” which is in the SD card’s boot directory, and add this as the last line in the file:

dtoverlay=dwc2

Save the file then:

Open the file “cmdline.txt”, find the word “rootwait” and, after it, insert the phrase:

 modules-load=dwc2,g_ether

You should end up with something that looks like “…=yes rootwait modules-load=dwc2,g_ether quiet…”:

Connecting to your Pi

To talk to your Pi’s Operating System you should be able to connect your Pi’s USB port to your computer’s or connect over WiFi. Either way you’ll need to use an ‘ssh’ program.

  • Windows: I use putty. Install the program and run it. Then you’ll need to enter:
    • Host Name: raspberrypi.local
    • Password: raspberry
  • Mac: I use the built-in Terminal (In your Applications->Utilities folder). Type in the command (don’t type in the “>”):
    • > ssh raspberrypi.local
    • Use the password: raspberry

If you go the WiFi route, you’ll need to find your Pi’s IP address and use that as the Host Name.

Update and Upgrade

Once you’re ssh’d in, and are connected the internet, you can update and upgrade the operating system. Type in the commands (without the “>”).

> sudo apt-get update
> sudo apt-get upgrade

The “sudo” means you’re giving yourself permission to run commands that could potentially mess up your system. The program you’re running is called “apt-get” which connects to the internet repositories with the latest updates and upgrades to your operating system and programs, and then downloads and installs them. The options “update” and “upgrade” specifically tells the “apt-get” program what you want it to do. Downloading and upgrading may take a while.

Enable Interfaces

You’ll also want to check that the interfaces to the GPIO pins are enabled, so you can build circuits and control them. Notes on this are here.

First check that your tools are installed and updated with the commands:

> sudo pip3 install --upgrade setuptools
> sudo apt-get install -y python-smbus
> sudo apt-get install -y i2c-tools

Then Activate the Interfaces. You’ll run the command “raspi-config” and then use your keyboard to tab through the windows to activate the I2C and SPI interfaces. These are just two different ways for the Pi to talk to the devices you plug into it.

> sudo raspi-config
---- Interfacing Options
-------- I2C
------------ Yes
---- Interfacing Options
-------- SPI
------------ Yes

To get this all up an running you need to reboot the Pi:

> sudo reboot now

For the OLED displays

To control the little OLED displays we have, install the adafruit-blinka, and OLED libraries:

> sudo pip3 install adafruit-blinka
> sudo pip3 install adafruit-circuitpython-ssd1306

Tornado Server

The tornado server allows us to create webpages on the Pi that we can connect to over WiFi that can be used to control devices connected to the Pi. Install tornado using:

> sudo pip3 install tornado

Now restart everything and we can get to work.

> sudo reboot now

Talk Timer

Arduino timer.
Arduino timer.

Given the idea that “learning situated in meaningful contexts is often deeper and richer than learning in abstract contexts,” (Lillard, 2007), I’ve been trying to orient our robotics program toward developing devices that we can use at school. Not only can these devices serve a useful purpose, but their presence around the school can, perhaps, inspire other students to want to make their own.

To this end, one of our first practical projects is a timer (by Joe A.) for when students give their presentations in Chemistry class. For the last round of presentations they had 20 minutes, so I had Joe build the circuits and program the Arduino to make the green light to be on for 15 min, the yellow on for 4 min, the red for 1 min, and then the piezoelectric buzzer would go off for 5 seconds and the red light would start blinking.

Joe did an awesome job, and the timer worked remarkably well. I did what we wanted it to do, and it actually worked to help them keep their presentations under time.

Human Jobs in the Robotic Future

After all the time I spent working with Raspberry Pi microcomputers and Arduino microcontrollers this summer, it was interesting to see Claire Cain Miller summary of a PEW report on “AI, Robotics, and the Future of Jobs“.

Miller provides some interesting quotes from the experts surveyed for the report. One quote stood out in terms of its perspective on education and pedagogy:

“Only the best-educated humans will compete with machines. And education systems in the U.S. and much of the rest of the world are still sitting students in rows and columns, teaching them to keep quiet and memorize what is told to them, preparing them for life in a 20th century factory.”

— Howard Rheingold, tech writer and analyst .

The Key Findings from the PEW report provides a good summary of their results:

Half of these experts (48%) envision a future in which robots and digital agents have displaced significant numbers of both blue- and white-collar workers—with many expressing concern that this will lead to vast increases in income inequality, masses of people who are effectively unemployable, and breakdowns in the social order.

The other half of the experts who responded to this survey (52%) expect that technology will not displace more jobs than it creates by 2025. To be sure, this group anticipates that many jobs currently performed by humans will be substantially taken over by robots or digital agents by 2025. But they have faith that human ingenuity will create new jobs, industries, and ways to make a living, just as it has been doing since the dawn of the Industrial Revolution.

These two groups also share certain hopes and concerns about the impact of technology on employment. For instance, many are concerned that our existing social structures—and especially our educational institutions—are not adequately preparing people for the skills that will be needed in the job market of the future. Conversely, others have hope that the coming changes will be an opportunity to reassess our society’s relationship to employment itself—by returning to a focus on small-scale or artisanal modes of production, or by giving people more time to spend on leisure, self-improvement, or time with loved ones.

— Smith and Anderson, 2014. AI, Robotics, and the Future of Jobs.

The full report is worth a read.

3d Printing at School

The  RepRap 3D printer.
The RepRap 3D printer.

One of the key ideas behind the design of the RepRap 3D printer we just built is that you should be able to print as many of the components as possible. So you can use your 3D printer to build other 3D printers. As a consequence, the printer does not come as a nice little box. It looks a bit jury-rigged. Multicolored coils of wire snake everywhere; circuit boards and integrated chips are exposed; nuts, bolts and stainless steel rods are accessible for easy adjustment; and the plastic–printed–components are still rough from the printer. It is all function, no aesthetics. All of which make it a wonderful teaching tool.

The three students who built it got a crash course in robotic assembly. They learnt how to wire a power source, strip and solder wires, and construct the motor-controlled bed and extruder. They also learned how to use constructive solid geometry (using OpenSCAD) to create 3d shapes–I required them to design and print their own models before I would let them download object files from the internet.

On the down side, though they did have to plug a RAMPS motor shield, stepper-driver chips, and connecting wires into the Arduino microcontroller, we did not have much time to go into the detail of what it all was about. Also, we only edited an existing configuration file when we tried to calibrate the machine, so they did not learn how the programming works. Having to use the Arduino did inspire me to get one, and I was quite impressed with their starter kit, so I’m working on a “Microcontrollers for Beginners” type class or elective that I can offer over the next school year.

Building a 3d Printer

Building the printer.
Building the printer.

I took three students to a workshop were we’re building a 3d printer. It’s run out of the Whitfield School. We spend today putting together the electronics to run the five motors we need to get the thing to work, and starting to put the frame together.

The frame is based on the RepRap Prusa i3 (via DIY Tech Shop), and the plastic parts that hold the rods, electronics and other metal bits together are 3d printed themselves.

Students learn to solder.
Students learn to solder.

The motors is run by an Arduino, which is great because I’ve been thinking about using one to operate the doors to the chicken coops.

Notes on hardware

Microcontroller

  • Arduino Mega 2560 R3
  • RAMPS Shield 1.4
  • RepRap StepStick Pololu A4988 (I think) stepper driver (plus heat sinks)

Filament: 1.75 mm PLA

Light and Sound with a Raspberry Pi

LED light circuits on a breadboard controlled to Raspberry Pi.
LED light circuits on a breadboard controlled to Raspberry Pi via a cobbler (connected to a ribbon of wires).

Although it took us a day to figure out how to get the Raspberry Pi to work–a faulty SD card turned out to be a major delay–we still had most of a week of the Creativity Interim for students to get some projects done.

That is, until it started to snow. We lost more two days.

Still, we had a small cadre of determined students, one of whom (N.D.) decided that she wanted to make the Pi play sounds to go with the blinking LED lights.

To do this she needed to:

  • Learn how to use the LINIX command line to connect to the Pi and execute programs.
  • Learn how to write programs in Python to operate the Pi’s GPIO (input/output) pins.
  • Learn how to make circuits on a breadboard connected to the Pi.

A Quick and Incomplete Introduction to the Command Line: Basic Navigation

We started by using the Terminal program on my Mac to learn basic navigation.

To see a list of what’s in a folder use ls:

> ls

For more details on the items in the folder, use the -l option:

> ls -l

To see all the options available for the ls command you can lookup the manual using man:

> man ls 

To create a new directory (e.g. Pi) use mkdir:

> mkdir Pi 

To change directories (say to go into the Pi directory) use cd:

> cd Pi 

Connecting to the Pi

I detail how to connect to a Pi that’s plugged into the wall via the local network here, but to summarize:

Use ifconfig to find the local IP address (under eth1).

> ifconfig 

Use nmap to identify where the Pi is on the network. E.g.:

> sudo nmap -sP 191.163.3.0/24

Finally, connect to the Pi using the secure shell program ssh:

> ssh pi@191.163.3.214

(the default password is “raspberry”)

Wiring an LED Light Circuit

A circuit that connects the #17 GPIO pin to a red LED light then to a resistor before going back into the ground (GND).
A circuit that connects the #17 GPIO pin to a red LED light then to a resistor before going back into the ground (GND).

We created an initial circuit going from the #17 General Purpose Input/Output (GPIO) pin to a red LED then through a resistor then back into one of the ground pins of the Pi. We’ll turn the current going through GPIO #17 on and off via our program on the Pi. The resistor is needed to reduce the amount of current flowing through the LED, otherwise it would likely get blown out. The circuit is shown in the picture where I’ve taken the wire ribbon out for the sake of visibility.

Wiring on a breadboard is quite simple if you remember a few rules.

First, the columns of holes on the sides are connected vertically, so the right end of the yellow wire (in the + column) is connected to the resistor.

Secondly, the holes in the middle are connected horizontally, but not across the gap in the middle. That’s why the GPIO pin #17 is connected to the lower end of the black wire, and the left end of the resistor is connected to the ground (GND) pin. The LED light reaches across the two gap to connect the two rows with the upper end of the black wire and the left end of the yellow wire. Without something to bridge the gap, the circuit would not be complete.

The resistor has a resistance of 420 Ohms. You can tell by the color bands. In the sequence–yellow, red, brown–the first two bars represent numbers (yellow=4; red=2) and the third number represents a multiplier (in this case brown represents 10x).

Light: Programming the Pi in Python

Once you ssh to the Pi you can start programming. We used the command line text editor Nano. A simple text editor is all you need to write simple Python programs. We’ll create a program called flash.py (Note: it’s important to include the .py at the end of the file’s name, otherwise it becomes hard to figure out what type of file something is, and the extension also clues Nano in to allow it to color-code the keywords used in Python, making it a lot easier to write code.

 pi> nano flash.py

You can then type in your program. The basic code for making a single light flash on and off ten times (see here) is:

flash.py

#!/usr/bin/env python
 
from time import sleep
import RPi.GPIO as GPIO

cpr = 17  ## The GPIO Pin output number

GPIO.setmode(GPIO.BCM) ## Use board pin numbering

GPIO.setup(cpr, GPIO.OUT) ## Setup GPIO Pin 7 to OUT

for i in range(10):
	GPIO.output(cpr, True)
	sleep(0.5)
	GPIO.output(cpr, False)
	sleep(0.5)
GPIO.cleanup()

This requires wiring a circuit to the GPIO pin #17. The circuit has a LED and a resistor in series, and circles back to the Pi via a grounding pin.

Run the program flash.py using:

pi> sudo python flash.py

Finally, let’s tell the program how many times to flash the light. We could create a variable in the Python code with a number, but it’s more flexible to set Python to take the number from the command line as a command line argument. Any words you put after the python in the command to run your program are automatically stored in an array called sys.argv if you import the sys module into your program. So we rewrite our flash.py program as:

flash2.py

#!/usr/bin/env python
 
from time import sleep
import RPi.GPIO as GPIO
import sys

cpr = 17  ## The GPIO Pin output number

GPIO.setmode(GPIO.BCM) ## Use board pin numbering

GPIO.setup(cpr, GPIO.OUT) ## Setup GPIO Pin 7 to OUT

for i in range(int(sys.argv[1])):
	GPIO.output(cpr, True)
	sleep(0.5)
	GPIO.output(cpr, False)
	sleep(0.5)
GPIO.cleanup()

So to flash the light 8 times use:

pi> sudo python flash2.py 8

Note that in your Python code you use int(sys.argv[1]) to get the number of times to flash:

  • sys.argv[1] refers to the first word on the command line after the name of the python file. sys.argv[0] would give you the name of the python file itself (flash.py in this case).
  • the int function converts strings (letters and words) into numbers that Python can understand. When Python reads in the “8” from the command line it treats it like the character “8” rather than the number 8. You need to tell Python that “8” is a number.

Sound: Using SOX

You can do a lot with sound–record, play files, synthesize notes–on the Pi using the command line program SOX. Install SOS (and mplayer and ffmpeg which are necessary as well) using:

pi> sudo apt-get install sox mplayer ffmpeg

Installation may take a while, but when it’s done, if you plug in speakers or headphones–the Pi has no onboard speakers–you can test by synthesizing an E4 note, which has a frequency of 329.63 Hz (via Physics of Music Notes), that lasts for half a second using:

pi> play -n synth .5 sin 329.63

Now play is a command line program that’s part of sox, so to use it in your Python program you have to tell Python to import the module that lets Python talk to the command line: it’s called os. Then you make a Python program to play the note using os.system like so:

test_sound.py

import os
os.system('play -n synth .5 sin 329.63')

And run the program with:

pi> sudo python test_sound.py

Combining light and sound

Now we bring the light and sound together a the Python program:

flash-note.py

#!/usr/bin/env python
 
from time import sleep
import RPi.GPIO as GPIO
import sys
import os

cpr = 17  ## The GPIO Pin output number

GPIO.setmode(GPIO.BCM) ## Use board pin numbering

GPIO.setup(cpr, GPIO.OUT) ## Setup GPIO Pin 7 to OUT

for i in range(int(sys.argv[1])):
	GPIO.output(cpr, True)
	os.system('play -n synth .5 sin 329.63')
	GPIO.output(cpr, False)
	sleep(0.5)
GPIO.cleanup()

which you run (repeating the note and light 5 times) with:

pi> sudo python flash-note.py 5

Notice that we’ve replaced the middle sleep(0.5) line with the call to play the note because we don’t need the delay since the note plays for 0.5 seconds.

Playing a Tune

N.D. wires LED's and resistors on a breadboard connected to a Raspberry Pi.
N.D. wires LED’s and resistors on a breadboard connected to a Raspberry Pi.

The student, N.D., spent some time working through this programming and adding wiring to the Pi breadboard in order to play the first few notes of Mary Had A Little Lamb. By the time we ran out of time, and she had to do her presentation to the rest of the upper-school, she’d come up with this:

red-light-flash.py

#!/usr/bin/env python
 
from time import sleep
import os
import sys
import RPi.GPIO as GPIO
os.system('play -n synth 2 sin 543.21')

cpy = 22
cpr = 17
cpw = 23

GPIO.setmode(GPIO.BCM) ## Use board pin numbering

GPIO.setup(cpy, GPIO.OUT) ## Setup GPIO Pin 0 to OUT
GPIO.setup(cpr, GPIO.OUT)
GPIO.setup(cpw, GPIO.OUT)

for i in range(int(sys.argv[1])):
	GPIO.output(cpy, True)
	GPIO.output(cpr, False)
	GPIO.output(cpw, False)
	os.system('play -n synth 1 sin 578.00')
	GPIO.output(cpy, False)
	GPIO.output(cpr, True)
	GPIO.output(cpw, False)
	os.system('play -n synth 2 sin 440.00')
	GPIO.output(cpy, False)
	GPIO.output(cpr, False)
	GPIO.output(cpw, True)
	os.system('play -n synth 1 sin 400.00')
GPIO.cleanup()

which is run (5 times) using:

pi> sudo python red-light-flash.py 5

Creating User-Defined Functions

(As a note to N.D., because we ran out of time before we could get to it.)

You’ll notice it takes four lines to turn a light on, turn the other lights off, and play the note. You’ll also note that you have to repeat the exact same code every time you want to play a specific note and it becomes a pain having to repeat all this every time, especially if you want to play something with more notes. This is the ideal time to define a function to do all the repetitive stuff.

So we’ll create a separate function for each note. Mary has a little lamb uses the notes E4, D4, and C4. So we get their frequencies from Physics of Music Notes and create the functions:

def e4():
	GPIO.output(cpy, True)
	GPIO.output(cpr, False)
	GPIO.output(cpw, False)
	os.system('play -n synth .5 sin 329.63')

def d4():
        GPIO.output(cpy, False)
        GPIO.output(cpr, True)
        GPIO.output(cpw, False)
        os.system('play -n synth .5 sin 293.66')

def c4():
        GPIO.output(cpy, False)
        GPIO.output(cpr, False)
        GPIO.output(cpw, True)
        os.system('play -n synth .5 sin 261.63')

now we can plug these functions into our code and call the notes pretty easily just by using the names of the functions:

flash-mary.py

#!/usr/bin/env python 

from time import sleep
import os
import sys 
import RPi.GPIO as GPIO

def e4():
	GPIO.output(cpy, True)
	GPIO.output(cpr, False)
	GPIO.output(cpw, False)
	os.system('play -n synth .5 sin 329.63')

def d4():
        GPIO.output(cpy, False)
        GPIO.output(cpr, True)
        GPIO.output(cpw, False)
        os.system('play -n synth .5 sin 293.66')

def c4():
        GPIO.output(cpy, False)
        GPIO.output(cpr, False)
        GPIO.output(cpw, True)
        os.system('play -n synth .5 sin 261.63')

cpy = 22
cpr = 17 
cpw = 23

GPIO.setmode(GPIO.BCM)


GPIO.setup(cpy, GPIO.OUT)
GPIO.setup(cpr, GPIO.OUT)
GPIO.setup(cpw, GPIO.OUT)

GPIO.setup(sp, GPIO.IN)

for i in range(int(sys.argv[1])):
	print "switch on"
	e4()
	d4()
	c4()
	d4()
	e4()
	e4()
	e4()

GPIO.cleanup()

which can be run (playing twice) with:

pi> sudo python flash-mary.py 2

Getting Started with a Raspberry Pi

Student wires the breadboard attached to a Raspberry Pi.
Student wires LED’s to a circuit on a breadboard attached to a Raspberry Pi.

Raspberry Pi‘s are small computers that are remarkably easy to use if you know what you’re doing. Unfortunately, I did not quite know what I was doing. On the other hand, fortunately, I had Mr. Schmidt available to give me the kick start I needed to get going. In this post, I’ll outline, in as much detail as possible, how we got started; how we helped a student put together a synchronized LED light and digital sound project.

You should just be able to plug your Pi into a monitor using the HDMI cable that comes with the starter kit (like this kit by Adafruit) and power it up. However, we did not have a monitor that could take an HDMI cable, so we had to connect the hard way: by plugging the Pi into an ethernet cable and finding it on the local network. This is what’s called a headless setup — with no monitor and no keyboard — and I followed a lot of Robert A. Wood’s instructions on headless setups.

Install the Raspbian Operating System for remote access

First you have to make sure you have a bootable operating system on the Pi’s SD card that will allow you to connect remotely through the internet. The card that came with the starter kit had the basic NOOBS operating system installed, but NOOBS does not allow remote access by default.

I downloaded the Raspbian raw image to my computer then copied the image to the SD card using the terminal program dd. Follow this procedure with caution because you can do a lot of damage if you copy the image over your computer’s hard drive (which is remarkably easy to do with dd). The procedure follows:

1) Once you plug the SD card into your computer it should mount automatically. You need to detect where it is mounted using (on a Mac running OSX) the diskutil program:

> diskutil list

This should give you a list of all of your mounted disks. Identify the one that is the SD card. It should look something like this:

Output from 'disktuil list'.
Output from ‘disktuil list’.

It shows my 4 gigabyte disk located at ‘/dev/disk1’.

2) If you’re absolutely sure you’ve identified the SD card you need to unmount it:

> diskutil unmountDisk /dev/disk1

3) Now if you’re still absolutely sure you have the right location of the SD card copy the image. Note that in the example below the option ‘if‘ means input file, while ‘of‘ means output file:

> dd if=~/raspberry/raspi/2014-01-07-wheezy-raspbian.img of=/dev/disk1

I had the devil of a time trying to install the raw image of the Raspbian operating system. After a few hours of frustration I finally pulled an SD card from my small camera and lo-and-behold the copy went through easily. So make sure you have a good quality card.

Talking to the Pi

Plug the SD card with Raspbian installed into the Pi, plug the Pi into a power outlet, then and plug an ethernet cable into the Pi. The Pi should boot up and connect to the internet automatically. Now you just have to find it from your computer. Mr. Schmidt helped a lot with this step, but I also used Pete Taylor’s instructions as well.

The ifconfig command will tell you your computer’s IP address. Look under the section en1.

> ifconfig

My IP address turned out to be 191.163.3.218.

To find the Pi I had to download and install nmap to locate all things on the local network. Once installed I used:

> sudo nmap -sP 191.163.3.0/24

You should find something labeled ‘Raspberry Pi’ with an IP address that’s almost identical to yours except for the last of the four numbers. I found mine at 191.163.3.214.

Now, you can log in to the Raspberry Pi using the username ‘pi’ and the password ‘raspberry’:

> ssh pi@191.163.3.214

And, ‘Bam’, you’re in.

Configure and Update

I used the configuration utility ‘raspi-config’ to expand the root file system to take up the entire SD Card: expand_rootfs:

pi> raspi-config

Update the software using the two commands:

pi> sudo apt-get update
pi> sudo apt-get upgrade

You can also set up the Pi for remote window access by running a Virtual Network Computing (VNC) server and using a vnc client (like Chicken on the Mac). I installed ‘tightvnc’ and started the vnc server on the Pi with:

pi> sudo apt-get install tightvncserver
pi> vncserver :1

We never did end up using the vnc window, however.

The light circuit

We hooked up the LED circuit to the output pin GPIO 17 in series with a resistor and then back into a ground pin of the Pi, pretty much as the Gordon’s Projects page describes.

Talking to the Circuits/Pins

In order to get the Pi to operate the LED lights you have to control the pins that communicate in and out. Our starter kit came with a ribbon cable and breakout board that connects the pins from the Pi to a breadboard, which makes it easier to build circuits.

But first we have to be able to control to the Pi’s pins. I tried two different methods. The first was to use wiringPi, which is a set of command line tools, while the second was to use the Rpi.GPIO library for the Python programming language. We found it was much easier to use Python for its ease of programming.

Command line: wiringPi:

To get wiringPi, download it with ‘git‘, go to its directory, then build it (Gordon’s Projects has the instructions):

pi> git clone git://git.drogon.net/wiringPi
pi> cd wiringPi
pi> ./build

Now you can manipulate pin 0 (GPIO 17, which is labeled #17 on the breakout board) by: 1) setting to output mode; 2) turning it on, and; 3) turning it off:

pi> gpio mode 0 out
pi> gpio write 0 1
pi> gpio write 0 0

The following short script (red-light-flash.s) turns the light on and off ten times:

red-light-flash.s

#!/bin/bash
# a single blinking led light attached to gpio0
# based on 
# https://projects.drogon.net/raspberry-pi/gpio-examples/tux-crossing/gpio-examples-1-a-single-led/

for i in `seq 1 10`
do
gpio write 0 1
sleep 0.5
gpio write 0 0
sleep 0.5
done

The script needs to be given execute permissions:

pi> chmod 777 red-light-flash.s

then run:

pi> ./red-light-flash.s

Python: Rpi.GPIO

As I mentioned above, it’s much easier to write programs in Python than to use shell scripts. So we’ll install the Python library, RPi.GPIO, to that allows us to communicate with the Pi. To get RPi.GPIO we first need the Python Development toolkit:

pi> sudo apt-get install python-dev

Then install Rpi.GPIO:

pi> sudo apt-get install python-rpi.gpio

To operate the GPIO-17 (turn it on and off every half second) we use the following program:

flash.py

#!/usr/bin/env python
 
from time import sleep
import RPi.GPIO as GPIO

cpr = 17  ## The GPIO Pin output number

GPIO.setmode(GPIO.BCM) ## Use board pin numbering

GPIO.setup(cpr, GPIO.OUT) ## Setup GPIO Pin 7 to OUT

for i in range(10):
	GPIO.output(cpr, True)
	sleep(0.5)
	GPIO.output(cpr, False)
	sleep(0.5)
GPIO.cleanup()

We run the program using the command:

pi> sudo python flash.py

Addendum: A Student’s Light and Sound Project

During our Creativity interim, one student chose to use the python program flash.py as a starting point to make a program to combine light and musical notes.

Youth Rover Robotics Competition

The Mars Society is sponsoring a Youth Rover Challenge using Lego Robotics kits similar to the ones we’re using for our robotics program. It’s relatively cheap to participate, so it might make for a good initial foray for my students.

Mr. Deitrich.