Home

Learn Programming with

1. 61 General safely RUES osi i oct roe E GS vict cvs areata teatro 62 Working With Heat 62 Working With Sharp Objects ccccccccccceccccsessccicsrctcastesesensvoesecratetcbeceseatearstsratetetesrsustduentateteseerstbueaveratatvievesratversterse 63 Wear Safety Glasses ics oe ooh loe oe ee one bone E E A teer slo E E occa 63 Fire Extinguishers at the REAY csceccscssssesscssesersscseseersnsacseesensaeseesesseeaeeenrancaeseeransacseesansaeseeseesanacsentansanses 63 Keepa First Aid Kit Handy ee 63 Work in a Ventilated Area rnnt tn RR Rn e RR RR RR RR Rn Ra ad 64 Organizing Your Workplace 1 eneseeeeee ener eene rn eren nnne nna nns nn strana 64 Bonus Soldering TECNIQUES icisiisri QE 65 SUMMA eee E 66 Chapter 5 The Web BOE edu icauacuiut kara uda cuu in sun auris wan UsE naga d cca n aUas aRa kd aun rau ndn EC 67 BoUEUGUBLID S oet ce edo bs i bos 68 The Connections OF the Web reete nemen acte cure est TaK ANENE 69 Web Communication Protocols eren tenete tete tete tenete tenens 69 LUBCONRURHIEIEEEE ELE 69 A Request Exarmple i utin idend nina anb ener eia eii d ea Pa i e i a s s s 70 CONTENTS Dur Web B l CONCE Dliia eee 70 Parsind WW ODP REIS ascii cece acess ene te a oat hb te ae bad en a a daau au Aak iant 71 Coding with Python MOCUICS x
2. THE RASPBERRY PI AND THE ARDUINO eoo head turn Arduino 1 0 5 head turn gt z include lt h 055 myservo 9 firstStopInterval 500 4000 secondStopInterval S00 4000 rightInterval 500 4000 leftInterval 500 4000 myservo 95 CfirstStopInterval myservo 94 rightInterval myservo 95 secondStopInterval myservo 96 leftInterval Arduino Duemilanove w ATmega328 on dev tty usbserial A400f01M Figure 14 2 A typical Arduino sketch In the figure you can see the code used to interface with a servo you include the Servo h library create a servo object called myservo and then write values to that object in order to move it Similarly to light an LED for example you simply set a particular pin to be an output and then send values of 1 or 0 to it to turn a connected LED on or off respectively As I mentioned before you can see that it s not Python code Lines are terminated with semicolons and blocks of codes are delineated with brackets not indentations Another nice feature of the Arduino s setup is that you can pull the Atmega chip off of the board and use it in a standalone breadboarded project In other words let s say you want to design a circuit on the Arduino that will use servos and motors to open and close a pet door in your house You can write and test the program on your Arduino board but then you can pull the chip and place i
3. lt w free bird m group 0 and you ll be rewarded with bird While regular expressions are very helpful in terms of finding sequences of characters in text and strings they re also not very intuitive and are far beyond the scope of this book We won t be spending much time on them here It s enough that you know they exist and you can spend some time learning about them if they interest you Coding with Python Modules When it comes to using different Python modules when coding your web spider you have quite a few options Many open source spiders already exist and you could borrow from those but it s a good learning experience to code the spider from the ground up Our spider will need to do several things in order to do what we need it to It will need to initiate TCP connections and request pages parse the received pages download important files that it finds and follow links that it comes across Luckily most of these are pretty simple tasks so programming our spider should be relatively straightforward Using the Mechanize Module Probably the most used module when it comes to automated web browsing mechanize is both incredibly simple and incredibly complex It is simple to use and can be set up with a few paltry lines of code yet it is also packed with features that many users don t fully utilize It s a great tool for automating tasks such as web site testing if you need to log into a site 50 times
4. playground 15 Linux file permissions 106 228 Media server clients 101 Linux OS X connection menu 109 Connect to Server dialog window Mac 109 NTFS drive 101 103 Samba apostrophe bug 107 configuration 104 105 Linux file permissions 106 restarting 107 108 Motion Sensor Cat Toy burned out LED 139 floating input 138 IR sensor and LED test setup 139 Parallax IR sensor 138 pullup pulldown resistor 138 Python script 138 Motor controllers 206 207 212 N National Marine Electronics Association NMEA 146 New Out Of Box Software NOOBS 10 12 New technology file system NTFS blkid results 103 description 101 file sizes 102 fstab file 103 My Book 102 103 NTFS 3g 102 NMEA See National Marine Electronics Association NMEA NOOBS See New Out Of Box Software NOOBS NTFS See New technology file system NTFS O Object oriented programming OOP 49 151 OOP See Object oriented programming OOP Open collector 207 208 Operating system OS Pi format card 10 NOOBS 10 PQ Parsing Web bot beautiful soup 4 BS4 71 print soup prettify 71 Python 71 regular expressions 72 INDEX PiFM 164 165 Python BDFL 33 data types dictionaries 42 43 lists 41 42 numbers 39 strings 40 41 tuples and files 43 44 IDLE see Integrated DeveLopment Environment IDLE OOP 49 PEP 20 The Zen Of Python document 33 programming definition 44 functions 48 49 IF tests
5. CHAPTER 4 ELECTRONICS AT 100 MPH Figure 4 8 Magnifying light Hot Glue Gun At some point you ll need to stick things to other things like one servo to another or a printed circuit board PCB to a robot s platform body and it may not be feasible to use screws or bolts One of the best ways to do this is with a hot glue gun Ignore the stigma of scrapbooking and paper plate macaroni designs and get a good glue gun Hot glue works surprisingly well in all sorts of applications wood to plastic plastic to plastic wood to metal and so on Assorted Glues Speaking of glue you ll probably want to pick up an assortment of other non hot glue gun glues Superglue is a must have get a brand name version though not a store brand as is modeling cement I also have a stockpile of 5 minute epoxy and rubber cement and recently discovered Gorilla Glue to be one of the most awesome glues yet You may also find a use for those cold welding sticks the ones where you mix two putty like substances together to form a clay that hardens to a steel like consistency Add tape to this list as well get some regular transparent tape some double sided tape masking tape electrical tape and of course duct tape Multimeter A multimeter measures different aspects of an electrical circuit voltage across certain points current and resistance See Figure 4 9 Whether you get an analog or a digital version is up to you but be prepared
6. From the main portion of the program we can start the thread by declaring a new myObject object a new thread newObject myObject and then starting it with newObject start The thread is now running with its own instance of the myObject called newObject Our thread as shown in the final code at the end of the chapter will be initiated with threading Thread init__ self Once it has been started it will continue to execute its function in our case collecting GPS data and taking pictures until we quit the program Setting Up Automatic Startup Because it s likely that we won t have a monitor or keyboard plugged in when we power up the Pi before we strap it to the plane we ll need to make sure that our GPS logging script starts automatically The easiest way to do that is to add an entry to the etc rc 1ocal file as explained in the sidebar What Is the rc local File In our case if our GPS logging code is called getGPS py and it s stored in our Documents plane folder we can add the line home pi Documents plane getGPS py to the rc local file Open it with sudo sudo nano etc rc local and add the line python home pi Documents plane getGPS py to the file before the last exit Oline in the file 152 CHAPTER 10 THE RADIO CONTROLLED AIRPLANE WHAT IS THE RC LOCAL FILE The rc 1ocal file is a standard part of the Linux kernel It is one of the system startup rc files and resides in the etc directory Aft
7. Once you set the mode you can then set each pin to be either an input or an output Users of the Arduino will probably recognize the concept here but this is what you type for the Pi GPIO setup 11 GPIO OUT GPIO setup 13 GPIO IN and so forth Once you set a pin as an output you can then send voltage to it turn it on by entering GPIO output 11 1 or GPIO output 11 True Subsequently you can turn it off by entering GPIO output 11 0 or GPIO output 11 False We ll use two pins to be servo controls one pin to power the laser pointer and another to read input from the IR sensor Controlling the Servo Servos are an important part of many many different applications from radio controlled vehicles to high end robotics A servo is at its heart nothing more than a DC motor However with the help of software you can have extremely fine control over the motor s rotation For example if you need it to rotate 27 5 degrees and then stop and assuming the servo is capable you can send it that command programmatically So how do you do that using the GPIO pins on the Pi Unfortunately you can t just plug the servo s signal wire the white one usually into a GPIO out pin give it a positive and negative voltage and expect it to work It may but then again it may not The answer lies in how to control servos As analog pieces of hardware they predate most of today s digital hardware including the Pi They operate using p
8. Z TECHNOLOGY IN ACTION Learn Raspberry PI Programming with Python LEARN TO PROGRAM ON THE WORLD S MOST POPULAR TINY COMPUTER Wolfram Donat www allitebooks com For your convenience Apress has placed some of the front matter material after the index Please use the Bookmarks and Contents at a Glance links to access them ty Apress www allitebooks com Contents at a Glance About the Author e XV About the Technical Reviewer eere nnne xvii Acknowledgments mee xix Introduction cscs ea ea ceases arse concen ais ae ean ude nel p c ER xxi Chapter 1 Introducing the Raspberry Pi 1eeeeeeeeeeeerennn nennen 1 Chapter 2 Linux by the Seat of Your Pants eeeereeneernennn nnn 15 Chapter 3 Introducing Python 1 eeeeeenee eee eenne nennen nnne nnn nnn nnn nnn 31 Chapter 4 Electronics at 100 MPH 1 eeeeeeeee eere nennen nnn 51 Chapter 5 The Web Bot E 67 Chapter 6 The Weather Station sssssscsssssssssssssesscssssessessessensesssssssseesssseseessssasansessas 81 Chapter 7 The Media Server sssunnusnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn nnmnnn 101 Chapter 8 The Home Security System sssunsussnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn
9. 214 1 2 reap trae ak ie pn c d ak d n da ak acpa s 72 Using the Mechanize Module niei rnnt tnr npn tad nnne nde aca anna ion 72 Parsing with Beautiful SOUP enean tn thiet tata ta than ta tht sa tasas satanas ana as 73 Downloading with the urllib Library eseesesseeeseeseeeeenennnn eene tntn tnn tntn tnn tn tntn trate tntn tnn 73 Deciding What to Dowrll dd a tte deut Uie la ooo io aiia oie 73 Choosing a Starting Poiht ertet neci tnnt eden a p cn dni mp Langue Lini igna dau 74 Storing Your FilgS 74 Writing th Python BOE Lees eatin tics ate Liisi 74 Reading a String and Extracting All the Links eese entente netten tnt tn nnns 75 Looking For and Downloading Files esses nennen ennt tntntn ena tntntn enitn ntn enata testen anas 75 RUMP 76 Creating Directories and Instantiating a List esssssesseeseeeeeeene tenente tnnt nnne tn nnns 77 The Final CoU isian iride poseen eet sie hoa cie can aeo t seated en Sion i Aie SEA bs Ea eene 79 SHUTTTGT V aar dara ETTA 80 Chapter 6 The Weather Station 11eeeeeeeee ee eeeeenne eere 81 A Shopping Hist er PaNis ese ore oe one a oi 82 Using the 12C Protocol Sinon scene EP RErnE ST nPE RPE rs ernire i rierie stare re crsrrer rberie st ererrt sfrerrerer orr
10. ATmega168 O LilyP ad Arduino w ATmega328 void flash int n LilyP ad Arduino w ATmegal68 Arduino Pro or Pro Mini SV 16 MHz w ATmega328 for int i 0 i lt n i O Arduino Pro or Pro Mini SV 16 MHz w ATmegal68 gt Arduino Pro or Pro Mini 3 3V 8 MHz w ATmega328 digitalwrite ledPin HIGH Arduino Pro or Pro Mini 3 3V 8 MHz w ATmegal68 4 Arduino NG or older w ATmegal68 Arduino NG or older w ATmega8 Arduino Duemilanove wi ATmega328 on devittyU SBO Figure 14 4 Selecting your Arduino board Before you upload the pi test script you just wrote it s a good idea to make sure that your board is connected properly and that you can upload a sketch to it To do that let s run the Blink sketch that comes with the Arduino IDE From the File menu select Examples 01 Basics Blink See Figure 14 5 The Blink sketch will open in a new window so that you don t lose your work for the pi test sketch The Blink sketch simply blinks the Arduino s embedded LED on and off and it s often used to make sure everything in your setup is correctly configured 220 CHAPTER 14 THE RASPBERRY PI AND THE ARDUINO sketch_mar22a Arduino 1 0 1 ER Edt Sketch Tools Help New Ctrl N Open Ctrl o Sketchbook AnalogReadS erial Close Ctrl w 02 Digital BareMinimum DigrtalReadsS erial m gt Save CtrtS o2 Analog gt gt Upload Ctrl U 95 Control Fade gt b gt gt SaveAs Ctrl Shift S
11. Ground GPIO17 GPIO27 GPIO22 GPIO10 GPIO11 Ground Figure 12 1 The GPIO pinout diagram 175 CHAPTER 12 THE SUBMERSIBLE Note Keep in mind that with GPIO setmode GPIO BOARD when you refer to pin 11 you re actually referring to the physical pin 11 which translates to GPIO17 in the diagram in Figure 12 1 not GPIO11 which translates to the physical pin 23 Once you ve set the mode you can then set each pin to be either an input or an output Users of the Arduino will probably recognize the concept here Type the following GPIO setup 11 GPIO OUT GPIO setup 13 GPIO IN and so forth Once you ve set a pin as an output you can then send voltage to it turn it on by typing GPIO output 11 1 or GPIO output 11 True and subsequently turn it off by typing GPIO output 11 0 or GPIO output 11 False If the pin has been configured as an input you can query the pin to see if a button or switch connected to it has been pressed However an important caveat here is that if the pin is merely declared an INPUT it is defined as floating and has no defined voltage level In this case we need to connect the pin to a ground so that it is always LOW 0 until we press a button This is done by putting a resistor between the pin and a common ground Luckily the RPi GPIO module allows us to do this in software by typing the following GPIO setup 11 GPIO IN pull up downzGPIO PUD DOWN At this po
12. IP address to be banned from the site in question Another piece of etiquette is controlling the speed of your bot s information requests Because bots are computers they can visit and download pages and files hundreds and thousands of times faster than humans can For this reason itis entirely possible for a bot to make so many requests to a site in such a short time that it can incapacitate a poorly configured web server Therefore it is polite to keep your bot s page requests to a manageable level most site owners are fine with around 10 page requests per second far more than can be done by hand but not enough to bring down a server Again in Python this can be done with a simple sleep function Finally it can often be problematic to fake your user agent identity A user agent identity identifies visitors to a site Firefox browsers have a certain user agent Internet Explorer has another and bots have yet another Because there are many sites that do not want bots to visit or crawl their pages at all some bot writers give their bots a fraudulent user agent to make it look like a normal web browser This is not cool You may never be discovered but it s a matter of common decency if you had pages you wanted kept private you d want others to respect those wishes as well Do the same for other site owners It s just part of being a good bot writer and netizen You may simulate a browser s user agent if you are emulating a browser for oth
13. and so on So we can write our script to add those lines to our final plane kml file We ll write our on the plane code to both take a picture and log the current GPS position every 30 seconds or so Because we re taking data points at specified times along a certain route we can use KML path function to create a visual record of exactly what our plane did The path will end up looking something like what you see in Figure 10 3 Figure 10 3 KML file in Google Earth 150 CHAPTER 10 THE RADIO CONTROLLED AIRPLANE Remember that because we re only polling the GPS unit every 30 seconds we won t have a nice curved line Instead the path will connect the places where the plane was at those intervals and the connections will be straight lines As you can see in Figure 10 3 I used a parking lot for my test flights my advice to a beginning flyer is to use a grassy field if you can as crash landings in grass are likely to be easier on your plane Everything in Alaska was covered by snow during my test flights so it didn t really matter where I tested things Using Threading and Objects An important programming feature we ll be using in this program is threads You may have seen them before I even use them in one or two of the other projects in this book Threads are important because they allow your program and processor to do several tasks at once and they don t tie up all the memory and processing power doing one simple task A simple
14. e Miscellaneous wires red black and so forth e Flat headed screw e Electrical tape e Popsicle stick e 9V battery e Acontainer on which to mount everything I used a short length of PVC pipe The Concept Behind the Toy The key to making this toy work is random motion If you program the toy to make a series of concentric circles one after another and then repeat the pattern it won t take long for your cat to recognize the pattern and get bored However by using Python s random or randint functions you can randomize the patterns and keep your cat and possibly your toddler entertained Another thing to keep in mind is that you will be randomizing the motion on two axes the x axis and the y axis while keeping the motion within certain bounds which is where the parameters of the randomizing functions and the movement extremes of the servos come in You will be using two servos but they ll be joined together so as to control the motion of one laser pointer To control the servos like several other projects in this book we ll use the Pi s GPIO pins and Python s GPIO library Another nice thing about this project is that the servos end up drawing so little power that they can be sourced with a simple 9V battery You still need to power them separately from the Pi always a good idea regardless of the project but you don t need a fancy battery setup as you do with many other projects 128 CHAPTER 9 THE CAT TOY C
15. eessssssseeeseseseeenenetn tnn tn ntn ena tn tn tn enata tein enata tein tnn 121 Connecting the Magnetic Sensor esses seen eene tntn tna tn ntn nate tnn inane tnit enata tn tn enata 122 oetting Up Pi S Gambera eie eite tote eere onte eee hte nada A TAA da na nd ca eee nane 123 Sending a Text Message from the Pi eessssssssssseseeesenetn enean tnn tna tn ntn enata tnmen ata tnnt nnns 123 Implementing the CallDack eren nnne nnne ta tnnt tatnen tatnen ta thia nas sata tests asa tasa saa aa 124 Connecting AIT ofthe BIS soie OE RR RR REDE EE 124 The Final Code cot toto batte tse nba ba boe EIE 125 J en mt RT 126 xi CONTENTS Chapter 9 The Cat TOY s sccisccsscccsstesctessateccesstdsdedsaiseceusdsssdaswadusscunttendadiucssusvercasdasmarssveustee 127 A hopping HSEDEPArIS 55 toe rne hai tiva Fon oa aa ea tasa ee 127 The Concept Behind tlie TO iouis 128 Creating and Using Random Numbers 1 cec ecce crece erc eer eere n nean a nnam annua 129 Using th GPIO AD Geary ioca ensi ak ck ananena anan Rub Cu acte ck ananman ugue b xac Ru ck u aa rua c anan ER TNR RES 130 Controlling the Servo eiis dandi enact 132 Constructing the Servo Mechanism s ssssesssssssnesnsusnonnrnnunnnnnnnununnnnnnunnnnnnnnunnnnnnnnunnnnnnnnnnnnnnene 134 Constructing the Laser Mechanism esee eere eere enne nnnn
16. geographic location and the best way to determine those values is to simply run the script Run the script preferably with a working compass nearby and compare the readings you get to the compass readings The side of the board with the soldered headers is the direction in which the board is pointed You may have to tweak the offsets bit by bit to the get the bearing to register correctly Once it s configured you have a way to measure the wind s direction we ll mount the compass to the anemometer s rotating shaft so that we can read the direction when we assemble the final weather station Connecting the Temperature Humidity Sensor The temperature and humidity sensor we re using the Sensirion SHT15 is one of the pricier parts in this build However it s also very easy to work with because there s no I2C protocol involved You ll first need to solder the included headers to it Like the compass the orientation of the headers is up to you I tend to solder headers on with the board facing up so I can see what each pin is as I plug the jumper wires into it Of course if I m going to plug the unit into a breadboard it means that I can t read the pins but that s the tradeoff Once you ve soldered the headers complete the following steps 1 Connect the VCC pin to the Pi s 5V pin 2 2 Connect the GND pin to the Pi s pin 6 3 Connect the CLK pin to pin 7 4 Connect the DATA pin to pin 11 Note With the pins labelle
17. if it s still open or start another session by typing python Then type import urllib to make it available for use The urllib library uses the following syntax image urllib URLopener image retrieve http www website com imageFile jpg imageFile jpg where the first parameter sent to the URLopener retrieve function is the URL of the file and the second parameter is the local file name that the file will be saved as The second file name parameter obeys Linux file and directory conventions if you give it the parameter imageFile jpg imageFile jpg will be saved two folders up in the directory tree Likewise passing it the parameter pics imageFile jpg will save it in the pics folder inside of the current directory from which the script is running However the folder must already exist retrieve will not create the directory Deciding What to Download This can get kind of sticky because there is so much out there Unfortunately or fortunately depending on your point of view a good deal of it is copyrighted so even if you find it for free it s really not cool to just download it Whatever you re looking for is out there That however is the topic for an entirely different book For the time being let s assume you re going to be looking for freely available information such as all works by Mark Twain that are in the public domain That means you re probably going to be looking for pdf txt an
18. like the terminal of a battery a chassis ground like an engine block in a car or the actual ground called an earth ground With the electricity basics under your belt let s talk about the tools you ll need to build your projects 53 CHAPTER 4 ELECTRONICS AT 100 MPH Required Tools for Robotics All engineers need good tools and as a budding hobbyist experimenter engineer you re no exception That dented banged up screwdriver sitting in your kitchen s junk drawer may be fine for prying staples out of the wall but if you try to use it for any delicate work on your projects you re just asking for trouble Likewise a pair of wire cutters with huge gaps in the teeth won t do you any good when you re trying to reach inside a tiny opening and clip the red wire before the timer reaches zero In order to build cool things you need good tools The following sections describe the necessary tools you should have Screwdrivers You need a good set of small jeweler s screwdrivers Spend the extra 10 and get a good quality set that will last you along time preferably one made out of hardened steel The set should have at least three regular and three Phillips screwdrivers with the regular sizes ranging from 3 64 of an inch to 1 8 of an inch and the Phillips sizes including both 0 and 1 A good screwdriver is worth its weight in gold because it s less likely to strip the screw or develop a damaged tip that fails to grip the screw at all
19. pages and repeat the download process If we do this several times we ve got ourselves a real web bot following links and downloading the files we want Let s do the second task first instantiating the list of links we mentioned at the end of the section dealing with reading strings and extracting links We can create a list at the beginning of the script after the import statements and add to it as we go To create a list we simply use linkList To add to it we add an elif block to our script if filetype in fileName image urllib URLopener linkGet http www irrelevantcheetah com fileName filesave string lstrip fileName image retrieve linkGet filesave elif htm in fileName covers both htm and html files linkList append link That s it If the fileName contains the type of link we re looking for it gets retrieved If it doesn t but there s an htm in it it gets appended to linkList a list that we can then iterate through one by one opening each page and repeating the download process The fact that we re going to be repeating the download process many times should make you think of one element of coding a function also called a method Remember a function is used in code if there s a process you re going to be repeating over and over again It makes for cleaner simpler code and it s also easier to write Programmers you ll find are very efficient people If we can code it once and reuse
20. s a preferred order to connecting the peripherals It may seem weird but it s possible even if highly unlikely that connecting power the monitor and the other parts in the wrong order could cause a voltage spike and fry your board So get used to hooking things up in this order and save yourself potential headaches down the line The order is as follows 1 Insert the SD card Connect the monitor Connect the USB peripherals keyboard mouse and or hub Connect the Ethernet cable ev ose e dw Connect the power As a matter of fact the most critical detail to remember here is to hook up the power last You can probably fudge on the others but power should always be last There s no on off switch as soon as you plug in the power LEDs should start lighting up and you should see a rainbow screen on your monitor 10 CHAPTER 1 INTRODUCING THE RASPBERRY PI Configuring the Pi When you start up the Pi for the first time with the NOOBS card you ll see a selection box with six choices Archlinux OpenELEC Pidora RISC OS RaspBMC and Raspbian Select Raspbian with your mouse and click the Install OS button at the top left of the window Click yes to confirm in the pop up box that follows and then wait while the image is written to your SD card It might be worth watching because the progress window has a few tips you can read while you wait When it s done click OK and the Pi will reboot to a black
21. servos that will be attached to the Pi Luckily there is a Python library that is specifically designed for this purpose that comes preinstalled on the Pi This library enables us to access the Pi s General Purpose Input Output GPIO pins and is called simply RPi GPIO To work with the library you may have to manually install two other libraries First make sure your Pi is up to date by typing sudo apt get update and then install the packages by typing sudo apt get install python dev and sudo apt get install python rpi gpio We can start typing our final code for this project Remember it s available as cat toy py from Apress com Now to access the Pi you call the following in the first lines of your program import RPi GPIO as GPIO 130 CHAPTER 9 THE CAT TOY Then configure it by typing GPIO setmode GPIO BOARD which lets you identify the pins as they are labeled on a standard pinout diagram shown in Figure 9 2 3V3 GPIOO aoo GPIO4 GPIO14 Ground GPIO15 GPIO17 GPIO18 GPIO21 Ground GPIO22 GPIO23 3v3 GPIO24 GPIO10 Ground GPIO9 GPIO25 GPIO11 GPIO8 Ground GPIO7 Revision 1 0 Figure 9 2 Pinout of GPIO pins Note Keep in mind that with GPIO setmode GPIO BOARD when you refer to pin 11 you re actually referring to the physical pin 11 which translates to GPIO17 in the diagram in Figure 9 2 not GPIO11 which translates to the physical pin 23 131 CHAPTER 9 THE CAT TOY
22. use the diagram in Figure 4 2 to better envision the relationships 52 CHAPTER 4 ELECTRONICS AT 100 MPH P l Current V Voltage R Resistance Figure 4 2 Common electrical equations As an example a common way of illustrating the different electrical concepts is with water and different sized pipes In a water circuit the water power is provided by a pump In an electrical circuit the power is provided by a battery In a water circuit the pump takes water at low pressure increases the pressure and sends the water on its way around the circuit In an electrical circuit the battery takes low pressure voltage increases its volts and sends it on its way around the circuit In both cases the current means the flow of either electrons or water around the circuit The resistance of the circuit is analogous to how large the water pipe is If the pipe is large it offers less resistance to the water flowing through it In a circuit if the wire has less resistance it allows the electrons to flow freely This in turn affects the power Power increases with resistance and current Think of power as the speed of the electricity if you have a certain amount of water flowing from the end of a hose and you hold your finger over the end increasing the resistance the speed of the water increases Increasing the resistance of the circuit increases the power There are byproducts to this of course Partially blocking the end
23. we know the robot has just advanced 1 foot This may seem like a lot of unnecessary math but it s important for you to understand how the encoder operates Once we attach the fins to the rotating shaft we could theoretically figure out wind speed based on the circumference of the fins and the speed ofthe shaft However my experience is that it s actually much easier to just experiment with known wind speeds and incorporate those speeds into our program so that s what we ll do To do that you ll need a partner somebody who can drive you around at predetermined sane speeds while you take wind speed measurements That means speeds of around 5 20 MPH not 80 To create your anemometer peruse your local hardware store until you find a small 1 8 inch square shaft that will fit in the square hole in the rotary encoder See Figure 6 3 84 CHAPTER 6 THE WEATHER STATION Figure 6 3 Square shaft Note As of this writing a 1 8 inch shaft fits perfectly in the rotary encoder s hole Next you ll need a pinwheel or something similar I used the windmill portion of a science kit that you can buy at your local craft store http amzn to 1koe1Sw for instance As you can see the shaft fits perfectly in the windmill s hole and the directional fin attaches easily to the back of the encoder See Figure 6 4 Figure 6 4 Encoder with wind vanes attached The entire mechanism needs to rotate that is it needs to be connecte
24. 04 Communication Upload Using Programmer Ctrl Shift U o6 Sensors ReadAnalogVoltage Page Setup Ctrl Shift p 07 Display Print Ctri p 08 Strings 5 09 USB Leonardo Preferences Ctrl Comma ArduinolSP Quit Ctrl Q EEPROM Ethernet Firmata LiquidC rystal SD Servo SoftwareS erial SPI Stepper Wire ne ne Ne SA SD ND SD Re p Arduino Duemilanove w ATmega328 on devittyUSB2 Figure 14 5 Loading the Blink sketch When the Blink sketch is loaded select Upload from the File menu and wait for the IDE to compile the Blink sketch and upload it to your board When the Arduino window displays Done uploading the red LED on your Arduino should be blinking slowly If not double check your connections and try uploading again You may get an error message stating that the COM port you selected can t be found and asking if you want to choose another one Take note of the suggested port you ll use that information later select it and upload your sketch Once you know that your connection is correct switch to the pi test sketch and upload it to the Arduino by choosing Upload from the File menu When it s compiled and uploaded in a terminal window start a Python session and type the following import serial ser serial Serial dev ttyUSBO 9600 221 CHAPTER 14 THE RASPBERRY PI AND THE ARDUINO Here you re importing the serial library and starting a communication over the USBO port at 9600 baud which is th
25. 45 46 loops 46 48 scripting vs programming language 31 32 scripts 38 39 terminal 37 Python gps module 148 Python modules beautiful soup 4 BS4 75 br open 75 download process 77 78 for loop 77 images directory 77 linkText string 78 mechanize Browser 74 module mechanization 72 operating system 78 parsing beautiful soup 4 BS4 73 retrieve function 77 String contains 76 str link 76 TCP connections 72 urllib library 73 URLopener retrieve 76 webbot py 75 web spider 72 R Radio controlled RC airplane additional parts 145 automatic startup 152 153 cgps stream 148 configurations 146 Google Earth on Mac 156 157 gpsd 146 GPS unit 155 KML conversion program 159 KML file 149 150 kml py 156 229 INDEX Radio controlled RC airplane cont lithium polymer batteries 154 overview of the setup 155 Pi on the plane s wing 156 plane kml 156 157 plane program 158 Process ID PID 157 Python s logging module 148 149 Raspberry Pi and GPS 145 threading and objects 151 152 USB car charger 154 Raspberry Pi Arduino see Arduino IDE Arduino code 218 Arduino s GND pin 224 ARM processor 215 Board audio and RCA video jacks 6 comparison devices 7 Ethernet and USB ports 6 GPIO pins 6 HDMI port 5 model B 4 power port 5 SD card 5 SoC 6 chips 2 complement 225 configuration 11 12 connection peripherals 10 Gertboard 224 hardware requ
26. 6 File testfile txt Figure 2 6 nano opening screen As you can see in Figure 2 6 common commands are listed at the bottom with the caret character signifying the Ctrl key To save a file type Ctrl X to exit You ll be asked if you want to save the file and under what name In general type Y and then Enter to save the file you ve opened or created 28 CHAPTER 2 LINUX BY THE SEAT OF YOUR PANTS Leafpad The other editor I should describe is Leafpad the full featured if lightweight GUI based text editor that comes preinstalled on the Pi To open it click the icon at the extreme lower left of the Pi s desktop and then select Accessories and then Leafpad See Figure 2 7 I Access ories R Debian Reference Y Education gt Q File Manager 2 Electronics gt E Galculator e Graphics gt 8 GNU Emacs 23 internet gt Image Viewer other gt E Leafpart D Programming LxTermingsimple text editor System Tools gt GD Root Terminal Preferences gt Bc archie Run Figure 2 7 Opening Leafpad As you ll see it looks like most editors you re used to such as Textedit or Notepad If you re comfortable using it by all means please do I don t mention it much only because its one main drawback is that it is usable only if you re working on the Pi s graphic desktop If you re remotely logged in to the Pi and are working solely through the command line Leafpad is inaccessible
27. Figure 13 2 The GPIO pins Since plugging the board into the Pi covers the Pi s GPIO pins those pins obviously need to be made accessible and they are as you can see in Figure 13 2 If you look closely at the pin numberings you ll notice that only the GPIO pins are in that row the 3 3V 5V and GND pins are elsewhere on the board Atmega Chip An interesting and helpful addition to the Gertboard is the Atmega 328P chip shown in Figure 13 3 the same chip used in most Arduinos It s a very useful microcontroller and in one of its other incarnations on the Arduino line of boards which I ll talk about in Chapter 14 it s used by many many hobbyists Having it available in an easily accessible form like this is something that many users on the Raspberry Pi online forums had been asking for 203 CHAPTER 13 THE GERTBOARD s 3 4 4 c DEG GG 3 43 4438 mvivrivivivivivivtririe 1 Li Lu LI 1 Figure 13 3 The Atmega chip Although the Atmega chip on the Gertboard is not bootloaded with the Arduino software it is definitely possible to add that software to the chip The pins circled in Figure 13 3 are the connections to the Atmega chip A to D and D to A Converters An important part of any board like the Gertboard is conversion analog to digital and digital to analog The four pins highlighted in Figure 13 4 and their associated IC manage those conversions for us 204 CHAPTER 13 THE
28. GPIO output 11 0 time sleep 0 0025 the results would most likely be something completely unexpected if it worked at all Instead what we can do is set the servo s signal pin pin 11 in our example case here to be a PWM output pin by entering p GPIO PWM 11 50 The 50 in this case sets the pulses to 50 Hz one pulse every 20 milliseconds which is what the servo requires to work We can then set the pin s duty cycle to 7 5 by typing p start 7 5 133 CHAPTER 9 THE CAT TOY If we put p start 7 5 inside a while loop the result is that the servo will move to the center position and then remain there Changing the duty cycle with p ChangeDutyCycle will allow us to move the servo in different directions which is what we re going for with the cat toy So for example to see your servo move back and forth try the following script import RPi GPIO as GPIO import time GPIO setmode GPIO BOARD GPIO setup 11 GPIO OUT p GPIO PWM 11 50 p start 7 5 while True p ChangeDutyCycle 7 5 time sleep 1 p ChangeDutyCycle 12 5 time sleep 1 p ChangeDutyCycle 2 5 time sleep 1 Running this script should make your servo sweep back and forth pausing for a second between each direction change All that s left for our cat toy script is to implement some random numbers Those numbers will determine which servo moves in which direction and for how long The result should be a rather random path in two dime
29. Model B image Raspberry Pi Foundation The Pi from here on we ll assume you have model B measures 85 6 millimeters mm by 56 mm by 21 mm yes it s obviously not made in America with some overlap for the ports and the SD card Referring to Figure 1 2 and moving counterclockwise around the card I ll explain the components in detail in the following sections www allitebooks com CHAPTER 1 INTRODUCING THE RASPBERRY PI The SD Card As you can see in Figure 1 2 a lot is packed into the card s small space One of the Pi s greatest space saving features is that there s no real hard drive like in your desktop or laptop the SD card acts like a solid state drive SSD You can change the size of that drive merely by switching SD cards within reason You must use at least a 2 GB card and at least 4 GB is recommended if you want to add any real software to your drive image You do Cards up to 32 GB have been tested and work but they are not guaranteed so be sure you back up your drive often if you decide to go with a bazillion GB card The Power Port The power port is merely a 5V micro USB input similar to what you see with many cell phones or tablets As a matter of fact a cell phone charger is one of the most common ways to power your Pi See Figure 1 3 Figure 1 3 Common USB power adapter A word of warning however The Raspberry Pi has no onboard power regulator If you re used to using the Arduino you know that
30. Summary This concludes your introduction to Linux While it in no way makes you an expert it should give you a healthy appreciation for all that this powerful OS can do You learned the basics of how to navigate through your file system using only the command line and you were introduced to the shell You ve also been introduced to the choices of text editors you have available to you and have hopefully chosen one that you are comfortable with Once you ve muddled around with it on your Pi enough you may find yourself installing Linux on one or more of your other machines It s okay I won t tell anybody In the next chapter I ll do my best to give you a solid introduction to Python 29 CHAPTER 3 Introducing Python You may remember from the first chapter that the impetus behind the creation of the Raspberry Pi was to make programming more accessible for everyone particularly kids To that end the creators wanted to release a relatively powerful computer that wouldn t cost a lot of money and one that anyone could simply connect to a keyboard mouse and monitor and start programming Another facet of that creation was to make programming easier and for that reason Eben Upton and his companions decided to include Python as an integral part of the Pi s operating system Python they reasoned was a powerful language yet it was simple enough for someone without any programming experience to pick up quickly In this chapter I ll give
31. Weller WES51 61 Soldering techniques cold solder joint 65 66 heat 65 surfaces and tin 65 Submersible construction plans completed submersible 197 connecting nunchuck 196 frame 192 marine epoxy 196 Pi camera placement 197 198 Pi s enclosure 192 193 underwater photography 199 200 USB car charger 196 controlling sub see Wii nunchuk Cron scheduler 188 extra Pi 173 final code 189 191 final control program 189 GPIO pins 174 176 parts 174 program remotely log in 187 188 Raspberry Pi camera board installation 176 178 System on a Chip SoC 6 T TCP See Transmission control protocol TCP Temperature humidity sensor 92 93 Text editors description 24 emacs 26 28 leafpad 29 nano 28 vim 25 26 vim vs emacs vs nano 25 Transmission control protocol TCP 69 U V UART interface See Universal Asynchronous Receiver Transmitter UART interface Universal Asynchronous Receiver Transmitter UART interface 146 159 W X Y Z Waterproofing procedures submersible motor for mounting 195 paraffin wax 195 pill bottle 194 sealing 193 Weather balloons camera board 168 festival 165 FFMPEG installation 165 166 final code 171 172 GPS data 164 GPS receiver 162 163 images 170 171 parachute 169 INDEX parts 161 PiFM installation 164 165 Pi preparation 161 166 regulator to balloon neck setup 167 168 tether cooler 169 threading and objects 167 Weathe
32. a special adapter you can access the nunchuk s wires and connect them directly to the Raspberry Pi without having to cut the connector from the end of the controller Figure 12 3 The Wii nunchuk 178 CHAPTER 12 THE SUBMERSIBLE The nunchuk communicates via a protocol known as I2C or IIC which stands for Inter Integrated Circuit If you re working your way through the projects in order you may remember the I2C protocol from Chapter 6 The Weather Station I2C was created by Philips in the early 1980s as a way for different devices to communicate on a single bus communication wire It has since undergone several revisions but the basic concept remains the same On an I2C bus one machine serves as a master and can be connected to a variety of different slaves Each machine can communicate on the same set of wires using a clock signal transmitted by the master to synchronize the communication Luckily for our purposes the Raspberry Pi can utilize the I2C protocol over some of its GPIO pins and the communication is relatively simple because there are only two devices communicating the Pi serving as the master and the Wii nunchuk as the solitary slave Attaching the Wiichuck Adapter The first thing to do is to solder a set of four headers to your Wiichuck adapter Using just a small amount of solder connect the headers to the adapter as shown in Figure 12 4 Like many commercially available boards the adapter is co
33. an issue with Mavericks and unfortunately is not something I can easily solve here 800 Connect to Server Server Address smb 192 168 2 42 Media Or Favorite Servers E vne 192 168 2 10 Remove Browse Connect Figure 7 4 Connect to Server dialog window on a Mac You now have a working Samba installation you can use to share anything you put into the folder and because of the permissions you gave it you don t have to worry about accidentally deleting a file in your Media folder from another device on the network The only way to add to or subtract from the shared folder is from the Pi itself a little security for your music and movies 109 CHAPTER 7 THE MEDIA SERVER Where s Python But wait Where s the Python in this chapter Well there is no Python in this chapter This is a good example of a situation where programming is not necessary the tools that are available are good enough just as they are and sometimes it s just as valuable to know when not to program as it is to know when fo program Summary In this chapter you learned a little bit about how servers and clients operate both on the Internet and over your home network You learned about getting the Pi and other computers notably Windows to play well together and how to share all of your media files across your home network accessible by any connected device using a free file sharing program In the next chapter you ll lear
34. callto import threading gives you the full power of threads and all they can do for you WHAT DO THREADS ACTUALLY DO Threads allow your computer to seemingly execute several tasks at once say seemingly because the processor can still execute only one process at a time but threads allow it to switch back and forth between processes so fast it seems to be executing them simultaneously As an example say you re working on your computer with a word processor open in one window and an Internet browser open in another While the word processor runs in one thread another thread executed between your key strokes keeps your browser updated still another one checks your email client for new messages and so on What we ll do with them in this program is use them to poll the GPS receiver By using a thread our main buffer won t fill up with data as we continue to get data yet we can still log the data in our log file for later use To use threads in the most efficient way possible we ll create an object called a Poller that will request information from the GPS receiver every so often let s say every three seconds using the gps module Every time we get a position reading we ll update the log and take a picture OBJECTS CLASSES AND FUNCTIONS OH MY Right about now you re probably starting to freak out a bit Objects Classes What s he talking about To quote Douglas Adams Don t Panic Consider this an easy non stressful intr
35. ceder mda CE A eam o eq m i Sede ae ne 60 pi raspberrypi Documents weather fj Figure 6 2 The i2cdetect tool 83 CHAPTER 6 THE WEATHER STATION In this case no devices are present which makes sense because we haven t plugged in any yet But you now have the necessary tools installed and running correctly Note If by chance you do have devices plugged in but nothing is showing try typing sudo i2cdetect y o instead The 1 or o flag depends on the Pi revision you happen to have If you have the Pi revision 2 you ll use the 1 flag otherwise the o flag should work Using an Anemometer An important part of any weather station is the anemometer the device that measures wind speed because wind speed is an important factor in any weather forecasting If it s a cold day below 32 F or 0 C for instance the wind speed plays an important factor in how cold it feels the wind chill According to the National Weather Service s wind chill chart a 15 MPH wind at 15 F makes it feel like 0 F and a 20 MPH wind at 0 F makes it feel like 24 degrees below zero Wind speed is important in this case in determining whether your extremities are going to freeze first or fall off first both equally unappealing if you ask me On the other hand if it s not particularly cold out the wind speed plays a part in how fast the next weather phenomenon is coming at you At 2 MPH that sunny day is going to take another few days to reac
36. connected servomotor a small motor that can be precisely controlled via software back and forth with one second delays Although not as powerful as the Pi the Arduino has done a lot to make electronics projects in general and microcontrollers specifically more accessible to the general public talk about how the Arduino and the Raspberry Pi complement each other well in Chapter 14 The Raspberry Pi while not brand new has been around for a few years Its creators Eben Upton Rob Mullins Jack Lang and Alan Mycroft first floated the idea of a cheap PC in 2006 Based at the University of Cambridge in the United Kingdom they were concerned that the demise of cheap personal computers like the Commodore 64 the Amiga and the Spectrum were adversely affecting young people s ability to program With desktop and laptop computers costing hundreds if not thousands of dollars kids and teenagers were forbidden from practicing programming on the family s main machine At the same time the creators realized that many university computer science curricula had been reduced to Microsoft Word 101 and How to create a web page The four creators wanted to raise the programming knowledge bar of incoming students and thus perhaps computer science and engineering courses would become a bit more robust Obviously a cheaper computer was necessary They played around with microcontrollers and various chips breadboards and PCBs but it
37. data streams need to be served in order and how forgiving of errors those streams can be When you request a web page with your browser there s a good bit happening behind the scenes Let s say you type http www irrelevantcheetah com into your location bar Your computer knowing that it s using the HTTP protocol first sends www irrelevantcheetah com to its local DNS Domain Name System server to determine to what Internet address it belongs The DNS server responds with an IP address let s say 192 185 21 158 That is the address of the server that holds the web pages for that domain The Domain Name System maps IP addresses to names because it s much easier for you and me to remember www irrelevantcheetah com than it is to remember 192 185 21 158 Now that your computer knows the IP address of the server it initiates a TCP connection with that server using a three way handshake The server responds and your computer asks for the page index html The server responds and then closes the TCP connection Your browser then reads the coding on the page and displays it If there are other parts of the page it needs such as PHP code or images it then requests those parts or images from the server and displays them as well Web Page Formats Most web pages are formatted in HTML HyperText Markup Language It s a form of XML eXtensible Markup Language that is pretty easy to read and parse and it can be understo
38. dataPin clkPin SHT1x GPIO BOARD temperature shtix read temperature C humidity shtix read humidity dewPoint shtix calculate dew point temperature humidity temperature temperature 9 5 32 fuse this if you d like your temp in degrees F print Temperature Humidity Dew Point format temperature humidity dewPoint Save this code as sht py and run it with sudo python sht py The script uses the functions defined in the Adafruit script read temperature C read humidity and calculate dew point to get the current values from the sensor which we ve connected to pins 7 and 11 Then it performs a quick conversion for those of us not using the metric system and displays the results You should get a line with your current conditions Temperature 72 824 Humidity 24 282517922 Dew Point 1 22106391724 As you can see it s a pretty self explanatory library Many of these libraries started their lives as written for the Arduino to communicate with them and thankfully they ve since been ported to run on the Pi See the side note regarding using existing code from earlier Connecting the Barometer Perhaps one of the most interesting parts of the weather station is the BMP180 barometer chip if only because changing air pressure is one of the best indicators as to what the weather is going to do next In general falling air pressure indicates a storm on the way and rising air pressure indicates good weather
39. directories are called subdirectories and they can be nested almost as far down as you care to contemplate e Special files representing hardware devices or some placeholder used by the OS e Executable files which are programs or shell scripts that contain instructions for the operating system The entire file system in Linux is contained within one root folder represented by a single Within that folder are subfolders such as bin home proc var and dev Each has more subdirectories in it In fact if you could zoom out and look at the file system in a 3 dimensional sort of way it would look similar to a giant upside down tree The home folder is your default home directory and each user has one on a Linux and Unix system Within that directory you are free to create execute and delete files If you need to manipulate edit or delete system files you may need to either log in as the root user or execute the command sudo Root User vs sudo In every Linux installation there is a user designated as the root who is able to administer all files on the system including system level files Most user accounts can t edit files in the var directory for example but the root user can Because of this power and the potential to misuse it even accidentally Linux users don t log in as root unless it s absolutely necessary when they do they log in do what they need to and log out again There is a saying among Linux geeks
40. dollars and can be used to drive incredible amounts of current and voltage up to 4 amps and 46 volts It s commonly used with hobby robots and is perfect for this type of application However though the chip is cheap connecting it to your Pi and the motors can be complicated because you need to use several 10nF capacitors and some flyback diodes to protect the Pi from voltage spikes coming from the motors For that reason I highly recommend getting the L298 motor driver board from Sparkfun as mentioned in the A Shopping List of Parts section It makes the connections much simpler you plug in the external source input signals from the Pi and output wires to the motors and you re done For the rest of the chapter I m going to assume you re using the Sparkfun board If you decide to breadboard the chip yourself some good schematics can be found online To control the sub and the motors we can modify the LED driving script I introduced earlier in the section The Nunchuk and LED Test but instead of turning LEDs on and off we re going to turn motors on and off and activate the camera Control will basically be as follows e joystick forward both motors spinning e Joystick left right motor spinning e Joystick right left motor spinning e C button pressed take still picture with camera e Z button pressed take video with camera To power the motors with the L298 board seven wires connect the Pi to the board three
41. eC E 5 Th Ethernet and USB POrts tete teen er tnter ires tani teea teri aiuta bre tei era atio ra best edad 6 The Audio and RCA Video Jacks ien tnter nnt rn n rn utn rn n in on rn Rn in on Hon Ru din EN Hnc 6 Irrtum 6 EARE EO I 6 Comparing Raspberry Pi to Similar Devices eeessssesseeeseeeseeeene nennen tnter tnn tnn tne tnn tnna 7 Hardware Requirements of the PI sosta RS Db opa ood n dom bu e Eus 7 Connecting to POW T E 7 Adding a MONON 52a 7 Addinga USB HUD issan ae a erara araia sreap oai eap ie cti eiitipieteittuete instet 7 Using sa Wireless USB Dongle 2 c terri treten ca tierna ke taceant e erue aaa aa aen incu aeaaea 8 The Pi Operating System sso ee ee 9 FOrMAatting the Card c 10 USING NOOBS ieseciss RES 10 vii CONTENTS Connecting thePernpheralS annona a mbari a a 10 Gonfig ring the Pis Tissin a aaaea UU ACTU UG AS UC MAR E ER CERE 11 Shutting Down TNE PT acera naa naa as ae retra aed ata d eva aane 13 summary ERE RES A AMETE SERENA TRE ET REOR RUE NAT 13 Chapter 2 Linux by the Seat of Your Pants eene 15 Getting Started with Linux on the Pi 1 sese eeee esee ee e
42. gps separate string by spaces coordinate string split line longitude coordinate 0 latitude coordinate 1 altitude coordinate 2 kml write longitude latitude altitude n write lt coordinates gt n write lt LineString gt n write lt Placemark gt n write lt Document gt n write kml An Summary In this chapter we connected a GPS to the Pi and read its input via the Pi s UART connections We then put that information into a Python log file We strapped the Pi and the GPS to a radio controlled airplane and logged our flight taking pictures every few seconds as we flew Then after landing the plane we transcoded our GPS log file to a KML file and put that file into Google Earth to see a satellite display of our final flight path This chapter demonstrated the true portability of the Raspberry Pi In the next chapter we ll take the Pi even higher by sending it in a weather balloon to the upper atmosphere 159 CHAPTER 11 The Weather Balloon You may be familiar with weather balloons Sometimes up to 20 feet in diameter they can be filled with helium given a small scientific payload and ascend to the upper limits of the atmosphere taking and recording various sensor readings as they go Then when the outside pressure becomes significantly less than the interior pressure of the balloon they burst and the payload falls back to earth with the assistance of a s
43. handy if you do a lot of editing and file manipulations in the terminal as we will in our projects See Table 2 2 22 CHAPTER 2 LINUX BY THE SEAT OF YOUR PANTS Table 2 2 Bash Keyboard Shortcuts Key or Key Combination Function Ctrl A Move cursor to beginning of line Ctrl C Stop currently executing process Ctrl D Log out equivalent to typing exit Ctrl E Move cursor to end of line Ctrl H Delete character in front of cursor Ctrl L Clear terminal Ctrl R Search command history Ctrl Z Suspend a program Arrow Left Right Move cursor left right one character Arrow Up Down Scrolls through previous commands Shift PageUp PageDown Move one page up or down in terminal output Tab Command or file name completion Tab Tab Shows all command or file name possibilities Again most of the shortcuts are self explanatory but the last two bear some additional explanations e Tab Pressing the Tab key when you re in the middle of typing a long file name will either complete the file name for you or offer you a list of choices For example if you are in the Desktop MyFiles directory and would like to quickly scan the myextralongfilename txt file simply type cat myextr and then press Tab Bash will fill in the file name for you assuming there are no other files with similar beginnings If there are others that start with myextr bash will make an error sound in this case press Tab again to see a list of choices
44. introducing you to the nuts and bolts of building electronics projects something many technical and programming books either gloss over or neglect completely There are safety factors to consider I very nearly had a small explosion when I shorted out a battery pack for instance as well as just good building practice For example you ll learn how to make a good solder joint and how to avoid slicing your index finger off with an X ACTO knife as well as the difference between a 40Q and a 40KQ resistor Of course if you re already familiar with all those things feel free to skip ahead to the good stuff the projects All of them can be constructed in a weekend or so or a month or two depending on your motivation level and length of your honey do list and all are programmed in Python I ll give you a shopping list of parts at the beginning of each project with places to get the parts and then we ll dive right in They don t necessarily build on each other nor are they in any particular order of complexity if you want to build the Cat Entertainer and skip the Home Media Server it s perfectly all right What kind of projects can you do with a Pi You d be surprised the Pi s small size belies its impressive computing power It has been used for everything from web servers to car computers carputers to cluster computing when hooked up in large groups I hope that after you finish this book you ll have not only some more ideas but the skills nec
45. is to combine them into one script We ve determined the movement parameters so let s write some functions that will be called from the main program loop to react to joystick movements and button presses The easiest will be the camera functions To take a still picture type def takeStillPic picNum Take still picture when C button is pressed call raspistill o image str picNum jeg shell True And for a video type def takeVideo Take video when Z button is pressed call raspivid o video mp4 shell True The first function takeStillPic picNum takes a picture using the system call raspistill with the name of the parameter picNum The second function takeVideo takes a video with the mp4 extension using the raspivid system call We ll do a from subprocess import callearlyin the program with all of our other imports It s a good programming practice to import all of your modules when you first start the program even though it s technically possible to import a needed module anywhere in the script Keeping your imports in one place can make it easier to debug the script later You ll also notice that takeStillPic takes an integer as a parameter if we keep a counter of each time we press the C button and send that count to the function we ll get a different image name image4 jpg image5 jpg and so on each time we press the button If we don t do that each time we call the function it wi
46. it that s ever so much better than typing it over and over and over again It s also a massive time saver 77 CHAPTER 5 THE WEB BOT So let s start our downloading function by adding the following lines to our webbot py script after the linkList line we added just a bit ago def downloadFiles html base filetype filelist soup BeautifulSoup html for link in soup find all a linkText str link get href if filetype in linkText image urllib URLopener linkGet base linkText filesave string lstrip linkText image retrieve linkGet filesave elif htm in linkText covers both html and htm linkList append link Now that we have our downloadFiles function all we have left to do is parse our linkText to get the name of the directory we ll need to create Again it s simple string manipulation along with using the os module The os module allows us to manipulate directories and files regardless of what operating system we re running First we can add import os to our script and then we can create a directory if needed by adding os makedirs You may remember that in order to simplify file saving we need to have a local directory on our machine that matches the web directory in which our target files are stored In order to see if we need a local directory we need to first determine that directory name In most if not all cases that directory will be the first part of our linkTe
47. large enough to add strips of Styrofoam on the sides if I need to change the buoyancy though I shouldn t have to seeing as how the Pi s enclosure is filled with air Creating the Pi s Enclosure You need a clear plastic container large to hold all your electronics I specify clear because your camera will be looking through it and needs to be able to see When you ve selected your container drill three small holes in it two for the wires to the motors and one for the wire to the nunchuk as you see in Figure 12 10 192 CHAPTER 12 THE SUBMERSIBLE Figure 12 10 Waterproof Pi enclosure Waterproofing the Motor Enclosures Perhaps the hardest part of this project is waterproofing the motors as they ll be outside the enclosure I used prescription pill bottles to hold mine First wrap the motor entirely with electrical tape to seal the large holes in the casing See Figure 12 11 Figure 12 11 Motor wrapped in electrical tape 193 CHAPTER 12 THE SUBMERSIBLE Then strip the ends from a short length of Ethernet cable and solder two of the enclosed wires to the wires from the motor When it s totally wrapped and the wires are connected drill two holes in the pill bottle one in the lid for the propeller and one in the base for the control wires Slide the wires through the bottle and make sure everything fits snugly in the bottle as shown in Figure 12 12 and Figure 12 13 Figure 12 12 Motor ready to ins
48. lose too much hard work if something happens to the card 173 CHAPTER 12 THE SUBMERSIBLE A Shopping List of Parts For this build you will need the following Raspberry Pi Raspberry Pi camera kit available from Adafruit Amazon and Sparkfun 1 Edimax EW7811UN USB wireless dongle Motor Driver dual L298 H bridge http www sparkfun com products 9670 Nintendo Wii nunchuk controller 1 Wiichuck adapter http www sparkfun com products 9281 Headers 2 DC motors Model propellers 2 battery packs the Lithium Polymer packs used by RC hobbyists are a good choice 1 waterproof enclosure think Tupperware or something similar 1 tube of 5200 marine waterproofing sealant PVC pipe and elbow joints Assorted zip ties Chicken wire or plastic mesh netting Wire red and black 18 gauge Ethernet cable 25 feet buy it in bulk if possible as you won t need the plastic terminals just the cable Wax Caulk Accessing the Raspberry Pi s GPIO pins One of the features that makes the Raspberry Pi so incredibly useful is its GPIO General Purpose Input Output pins Using a specific Python module that comes preinstalled on the Pi the GPIO pins can be directly controlled sending voltages to external devices and reading inputs that can then be used in programs GPIO WHAT S THE BIG DEAL GPIO pins are like some of the ports on an old computer An easy way to interface with the external world used to be either the s
49. motors are waterproofed you can assemble the final product Run the wires from each motor through the holes in your container and connect them to the motor controller board the same way you did for testing When all the wires have been fed through the holes use the marine epoxy to seal the holes Warning The 5200 sealant is extremely sticky and messy and if you get it on your skin it won t come off Wear gloves and do all your work outside if you can Also don t be stingy with the sealant you re trying to protect all your electronics so make sure there s no way water s getting into your enclosure When the holes are sealed make sure all your electronic connections are sound and put the Pi and the motor controller into the enclosure Use a small piece of tape or poster putty which is what I used to press the camera against the front wall of the enclosure and to hold the various boards in place Use a small breadboard to connect your grounds and add your two batteries one for the Pi and one for the motor controller When you power your Pi with a battery you must use a 5V supply because the Pi does not have an onboard voltage regulator You can experiment with different battery combinations or you can use a voltage regulator to do the work for you For all of my portable Pi work I have hacked a USB car charger seen in Figure 12 16 for that purpose because it delivers 5V and about 1 amp perfectly Figure 12 16 USB car cha
50. nnnm 164 IGI RISUS mmc 165 installing FEMPE G e iue o ducebat te ll 165 Prepara Ihe Poo esu EOE E RR ces eyes RR EXER RR RENS EXRER RR NER EXRER RD ERR CREER ut 166 Using Threading and Objects 1 esee eeseee eese eren ennt nnn nnn nnn nas 167 Connecting the Bits scsi assesses ease ves sass eese dps aee ae kPE ERE Ps ERE PR PRO REPE PEERS REPE ERIS IEE RUE 167 Reviewing the drill m 170 Tre Final Ug t at et teh o ttt tat teca t edt 171 Sulla A E eoe IE ELE ELE LEE UE 172 Chapter 12 Th Submersible coin coa ria on sni nns suckauaS ru CYa Cann sup CERu nS co d Ceu EDS aU E Rau ap eREaN no 173 A Shopping BSEOEPOEIS entes eo oec oom m eco oen coe merces 174 Accessing the Raspberry Pi s GPIO pins 1eeesseesresre ener enne 174 Installing the Raspberry Pi Camera Board eese ener eren 176 orte TE B voee 178 Attaching the Wiichuck Adapter esssisssssessseseene tenete enean ntn enata tnit enata th tn tn atate tn tn ane senin 179 Activating th duda 180 Testing the NUNGHUK eer 181 Reading from the NUnch k 3 seen eterna tenera eei cedaenceandnceasendeecds 182 Controlling the Sub Motors and Camera with the Nunchuk essent 185 Starting the Program Remotely 1 eee creer eere sre erenn enne nn enn annaamaaman 187 Quse no Buren c ener 189 da
51. no less Again because it bears repeating The Pi has no onboard voltage regulator You can t plug in a 9V battery or wall wart and expect it to work Either use something like a cell phone charger that puts out 5V most of them do or get a good power supply from an online electronics store or from the place where you bought the Pi The power supply will also need to supply at least 500 milliamps mA and preferably more like 1 amp A If it sources only 500 mA be prepared for some funky behavior like the mouse and keyboard not working when the wireless adapter is plugged in I recommend 1A Adding a Monitor The next peripheral you ll need at least at first is a monitor with either HDMI or DVI capabilities If all you have is DVI input that s all right because HDMI to DVI converters are everywhere After you ve got it set up and all the necessary software is installed you can run the Pi in a headless configuration What that means is that you can log into it from another computer with either SSH Secure Shell or even a VNC Virtual Network Computing client But at first you ll need a monitor so that you can see what you re doing Baby steps Adding a USB Hub You re probably going to want a USB hub at some point Model B has two USB ports which means you can plug in a keyboard and a mouse and you ll be sitting pretty However if you want to go wireless and at some point you will trust me you re going to need at least three USB por
52. now have a good grasp of how to use Python functions to repeat tasks at a given interval You ve also done more fabrication here than any other project so far now you can take a break because the next project the media server requires no construction whatsoever 100 CHAPTER 7 The Media Server The concept behind a media server is its ability to store all of your media files music and movies in one central location and then stream them from that location to whatever device in your house you choose These days almost every media device and some non media devices can hook up to a network if not the Internet then at least your home network This means that all of these machines except for perhaps the refrigerator can become clients streaming media files from a central server This is standard networking language the computer that stores files whether they be media files spreadsheets or web pages is called a server and computers that request those files are called clients As it happens the Pi is perfect to act as a server That s because there s very little computing power necessary an Arduino can actually be a media server and it s about 100 times less powerful than the Pi and storage space is not a problem because you can stream media files from any connected storage device such as an external hard drive The Pi can stream files to any compatible device But it s a Linux box I hear some of you screaming from
53. of a hose increases the friction at the mouth of the hose and thus the heat Likewise increasing the resistance of a circuit often means increased heat Heat is bad for circuits especially fragile items like integrated circuits ICs so many electronic components that produce heat because of internal resistance among other reasons often have a heat sink built in to dissipate the heat they create At its most fundamental electricity is nothing more than electrons moving back and forth along a wire or some other path That path is always the path of least resistance Given the choice of two ways to travel electrons will always take the easiest path whether it s through a wire a screwdriver or a human torso Your goal when working with these electrons is to ensure that the easiest path does not involve your body You won t always be successful I ve been shocked more times than I can count In fact in addition to the multiple electric shocks I ve experienced with batteries and power supplies I ve actually been struck by lightning three times A conscientious experimenter should try to reduce these incidents if for no other reason than they can hurt Rubber gloves can help though wearing them all the time is a bit impractical as can rubber boots or rubber soled shoes The reason rubber boots are a good idea in addition to them being extremely fashionable is that electrons always want to connect to ground That ground may be a power ground
54. on and off led_drive which takes as parameters the number of repetitions reps whether we re lighting single or multiple LEDs at a time multiple and direction We can then use these parameters to do nifty things with the LEDs Back in the main function we then simply go through a predefined list of calls to the led drive function That s the whole script To set up the board make sure the output jumpers are set as described earlier Then depending on which Pi revision and Gertboard design you have connect jumper wires from the GPIO header section section J to the row of output headers section B When you re done the board should look similar to Figure 13 11 211 CHAPTER 13 THE GERTBOARD Figure 13 11 Jumper positions for the LED script Now you can simply run the script by typing sudo python leds rg py and you ll be rewarded with some fancy light sequences No we didn t write any elaborate Python here but that s sort of the point Simply by connecting a few wires we were able to get some pretty impressive results with just a few lines of code no external LEDs or resistors required The output pins can be connected to any number of external devices for example a batch of tone generators perhaps You could write a script that activated the generators in certain sequences and thus play a tune Experimenting with Motor Controllers The next section of the board we can play with is the motor controller secti
55. rolls across the table and there is the soft muttering of an argument No Han shot first Figure 2 1 The Linux users playground 2006 Marcin Wichary However fear not While some of us still heartily embrace that culture and all that it stands for that doesn t mean you have to Linux has come a long way since it was first introduced and it is now not only a real powerhouse of an operating system but also extremely user friendly at least most of its distributions are The most popular flavors of Linux are Ubuntu and Mint Both are visually so similar to Windows and Mac that many people find switching to them fun and easy Another popular version of Linux is Debian which is the distribution that the Pi s operating system Raspbian is based on When it first began Debian was the only distribution of Linux that was truly open allowing any developer and user to contribute It still remains the largest distributor of Linux that is not a commercial entity 15 CHAPTER 2 LINUX BY THE SEAT OF YOUR PANTS Okay enough horn tooting In order to really use the Pi you ll need atleast a basic understanding of Linux and how it works So let s get started THE LINUX STORY Linux is an operating system loosely based on the Unix operating system It has always been free and open source and it was first released in 1991 by its creator Linus Torvalds It is written in the C programming language and was originally designe
56. the area is dry use the small screws to attach the popsicle stick to the servo horns When you re done you should have a device that looks like Figure 9 7 136 CHAPTER 9 THE CAT TOY Figure 9 7 Laser mounted to servos A word of caution here take some time and position the laser pointer and its associated servo so that the laser can spin freely no matter where in the cycle the two servos are Obviously the easiest way to do this is to remove the screws holding the servo horns to the servos and reposition the horns based on the servos travel arcs Then run the two servos through all possible positions and make sure that your mechanism doesn t bind at any point in its motion Since standard servos only travel through an arc of around 180 degrees you should be able to find a suitable position for all the parts The last integral part of this project is connecting the motion sensor Connecting the Motion Sensor Not only does the motion sensor shown in Figure 9 8 save your batteries but it also seriously contributes to the cool factor your toy turns on only when your cat or a dog or a roommate or a Sasquatch comes near it 137 CHAPTER 9 THE CAT TOY Figure 9 8 Parallax IR sensor Hooking up the IR sensor is simple the positive and negative pins are connected to power and the third pin the leftmost pin in Figure 9 8 is connected to one of the Pi s GPIO pins configured as an INPUT When the sensor detects moti
57. the back row I need to stream to my Windows laptop Not a problem the software we ll use to act as the server allows Linux servers and Windows clients to play nicely together Regarding your media files I m going to assume you are an upstanding law abiding citizen who has paid for all of your movies and music and have amassed quite a collection the correct legal way Right Right Let s begin with the parts you ll need A Shopping List of Parts This project requires almost no parts All you ll need is your Pi and an external USB hard drive large enough to store all of your files The Pi should recognize most modern external drives but I recommend that if you purchase a drive for this purpose you plug it into the Pi and make sure everything works before you start transferring gigabytes of files to it to be streamed Using an NTFS Drive The USB hard drive you use needs to be formatted as an NTFS New Technology File System drive NTFS is a Windows format that often requires some special handling in order to be compatible with Linux FAT32 was the format most often used prior to NTFS and Linux and Unix had no problems reading from it or writing to it but FAT32 cannot handle file sizes over 4 GB a limit easily exceeded by one high definition movie file Thus we ve moved to the NTFS format which can handle file sizes up to 16 TB without breaking a sweat FAT32 also had issues with total drive sizes depending on the size of file cluste
58. the button At this point you should have something that resembles the image in Figure 9 6 Figure 9 6 Completed laser pointer mechanism If you want to test your work use a few alligator clips to connect the screw s point to pin 6 the ground pin on the Pi and connect the body of the pointer to pin 1 3 5V The laser should light showing you are powering it directly from the Pi s power pin If nothing happens make sure the screw head is pressing on the spring the power button is securely taped down and all your connections are solid Once the connections are solid you re ready to mount the laser to your two dimensional servo contraption Connecting the Laser to the Servo Connecting the laser to the servo is probably the easiest part of the project If you re like me you don t want to permanently attach the laser to the pan and tilt servo setup you ve got because that setup can come in handy with other projects as well So we need to find a way to temporarily attach the laser to the servo horns I used a popsicle stick to pull this off We can glue the laser to the popsicle stick and then screw the stick to the servo horns This can be done with either the screws that came with the servo you still have them don t you or the smallest screws you can find in your workshop Trust me those are really tiny holes in the servo horn Using a strong glue again I like Gorilla Glue affix the laser assembly to the popsicle stick When
59. the output as if you had run the script A more complicated test uses elif and else such as the following X spam if x eggs print eggs are better when they re green elif x ham print this little piggy stayed home else print Spam is a wonderful thing 45 CHAPTER 3 INTRODUCING PYTHON Obviously this code outputs Spam is a wonderful thing When the program is executed the computer checks the first if If that statement is determined to be true it executes the indented block directly after it If that statement is false it skips the indented block and looks for an elif which it then evaluates Again if it s determined to be true or if there is no elif the computer executes the following block if not it skips that block and looks for another elif or an else Three points here are important enough to mention First remember that if an if statement is determined to be false nothing in the following indented block is executed the computer jumps straight to the next unindented line Second Python like other languages uses the double equal signs to indicate a test for equality A single equal sign is used for assignments a double is a test I mention this because every programmer and I do mean every programmer has at some point used a single equals sign in an if statement and their program has done all sorts of funky unexpected things as a result You ll do it too but I hope to save you a
60. to spend a little money because a good multimeter is an incredibly valuable tool It can be used to trace electrical shorts ensure that you re using the correct voltage and figure out how much resistance exists between two points in a circuit 57 CHAPTER 4 ELECTRONICS AT 100 MPH Figure 4 9 Analog and digital multimeters Owww digimeter com When choosing your multimeter make sure it can measure both AC and DC voltage levels because it s likely you ll be using both at some point It should be able to measure resistance and continuity as well as current The most important characteristic to look for however is ease of use If you don t know how to use the multimeter you won t use it and you d be wasting an important tool So get one you like that makes sense to you and then spend some time with the manual learning how to use it Power Supplies When it comes to powering your experiments and projects there are a few different routes you can take Obviously you ll often be using batteries or battery packs and I ll talk about those for each specific project However when it comes to powering a prototype or just determining if a particular configuration works you can t go wrong with a wall wart the AC to DC converters that come with almost all electronic devices these days You can get an adjustable wall wart at an electronics store which I recommend but you can also haunt your local thrift store Somewhere buried in the b
61. wasn t until 2008 that the idea became more feasible Chips were becoming smaller cheaper and more powerful thanks to the explosion in mobile devices These chips enabled them to plan a device that would be capable of supporting multimedia not just command line programming which they felt was important See Figure 1 1 Young people were more likely to be interested in a media capable device and thus more likely to try programming on one 2 www allitebooks com CHAPTER 1 INTRODUCING THE RASPBERRY PI d Figure 1 1 Eben Upton s 2006 Raspberry Pi prototype image Raspberry Pi Foundation In 2008 the original four creators along with Pete Lomas and David Braben formed the Raspberry Pi Foundation the Foundation and three years later the first mass produced Pi rolled off the assembly line Note The name Raspberry Pi is a nod to the number of microcomputers named after fruit in the early days such as Apple and Tangerine and the Pi comes from the Python scripting language Within a year the Foundation had sold over one million units The founding members have said many times that they were dumbfounded by the explosive interest in their device Their original goal of putting a cheap programmable device in the hands of educators and their students has come to fruition However it has become much more than that Apparently they were not the only ones who were missing the ability to program on a cheaper machine hobbyis
62. we ll need to rename the downloaded file so that we can use it In this case the file we downloaded is named NJZOTr Rename it by typing mv NJZOTr Adafruit BMPO85 py 94 CHAPTER 6 THE WEATHER STATION There s nothing to install here so we can jump right into using the library to communicate with the chip In a new Python script in the same directory enter the following from Adafruit BMPO85 import BMPO85 bmp BMPO85 0x77 you may recognize the I2C address here temp bmp readTemperature temp temp 9 5 32 fif you re not in one of the 99 of countries using Celsius pressure bmp readPressure altitude bmp readAltitude print Temperature 4 2f F temp print Pressure 4 2f hPa pressure 100 0 print Altitude 4 2f altitude As the script for the temperature sensor did this little bit of code uses the prewritten library and its functions to read the necessary values from the barometer chip When you run it you should get something like Figure 6 11 pi raspberrypi Documents weather sudo python bmp 85 py Temperature L 6 re d titude Q pi raspberrypi Documents weather J Figure 6 11 Output of BMP180 pressure sensor You can now read from all of your sensors so it s time to put everything together Connecting the Bits An important part of building this weather station is putting everything or at least the compass on a rotating platform so that you can determine the wind s dire
63. web forms or dynamic content and it looks pretty much like this HTML lt HEAD gt TITLE Links html TITLE lt HEAD gt lt BODY BACKGROUND mainback jpg BGCOLOR 000000 TEXT E2DBF5 LINK EE6000 VLINK BD7603 ALINK FFFAFO gt lt br gt lt H1 ALIGN CENTER gt My Favorite Sites and Resources lt H1 gt lt br gt lt H2 gt Comix Art Gallerys and Points of Interest lt H2 gt lt DL gt lt DT gt lt A HREF http www alessonislearned com index html TARGET blank gt A Lesson Is Learned lt A gt lt DD gt Simply amazing Great ideas great execution I love the depth of humanity these two dig into Not for the faint of heart and so on until the final closing lt HTML gt tag If a spider were receiving this page over a TCP connection it would first learn that the page is formatted in HTML It would then learn the page title and it could start looking for a content it has been tasked to find such as mp3 or pdf files and b links to other pages which will be contained within lt A gt lt A gt tags A spider can also be programmed to follow links to a certain depth in other words you can specify whether or not the bot should follow links from linked pages or whether it should stop following links after the second layer This is an important question because itis possible that if you program too many layers your spider could end up trawling and downloading the entire Internet a
64. with the arrow keys just as you can in Insert mode but you can t change or add anything until you type i To save a file make sure you re in Normal mode by pressing the Esc key at least once Then type w without the quotes and press Enter To save and exit at the same time type x again without quotes and press Enter Obviously if you re in Insert mode when you type these characters all you ll succeed in doing is adding W Or X to your document Vim takes a lot of getting used to and many people have trouble adjusting to the two different modes of operation If you decide you like it there are many tutorials online to teach you to use it to its full potential Using Emacs Emacs to me at least is a bit more intuitive than Vim particularly when you re first starting to use it To start open a terminal and navigate to where you want your test file such as the desktop Once there type emacs testfile txt Emacs will look for testfile txt open it if it exists and create it and open it if it doesn t You ll be faced with a blank pane like the one you see in Figure 2 5 26 CHAPTER 2 LINUX BY THE SEAT OF YOUR PANTS File Edit Options Buffers Tools Help U testfile txt All L1 Text 2 lllIllllIlIlII lIIIllIIIlIIlIl 4 gt New file i Figure 2 5 Emacs opening screen You can start typing immediately Table 2 3 lists the most common commands in emacs Table 2 3 Common Commands i
65. writing which is why you ll need to add it Once NTFS 3g is installed plug your drive into your Pi You ll probably be greeted with a popup window asking what to do just select Open in File Manager and continue Once you know you can read it by viewing its files make sure you can write to it by opening a terminal and creating a directory which is only for testing like this cd cd media ls cd My Book or whatever your drive is named use ls to find the name mkdir test Ifthe test folder appears you can move on If not make sure you installed NTFS 3g and reboot the Pi if necessary You may have noticed the fact that My Book is in quotes in the preceding command That s because while file names can contain spaces you need to account for the spaces when you re using the command line If you need to change directories cd to a folder called My Book just typing the following line will give you a file not found error because the OS looks for a folder named My and then stops looking cd My Book The way to account for spaces in file names is to either use quotation marks around the name or escape the space with a backslash like so cd My Book We need to create a Media folder in the media directory of the Pi where we ll be storing all of our music and movie files We can create subdirectories in there later but for now we just want to make sure that every time we boot up our Pi the external drive will get mount
66. you can safely power it with up to 9V and go on your merry way If you try that with the Pi you ll have yourself a nice paperweight Don t go above 5V if you re not sure what your charger puts out measure it with a multimeter Better yet all web sites that sell the Pi also sell a variety of chargers guaranteed to work with it Me Iuse the old charger that came with my Blackberry Torch Yes I owned a Blackberry Don t judge me In case you were thinking of asking Yes you can power the Pi with batteries though performance can get funky as they discharge and power levels drop below 5V Probably the easiest way to do it is to use a 9V battery or a bank of 4 AA batteries and funnel it through a voltage regulator or use a battery pack such as those found in Remote Control cars I ll discuss that as well in chapters where the project involves a mobile Pi The HDMI Port The Pi is equipped with an HDMI High Definition Multimedia Interface output port and many argue that this is truly where the Pi comes into its own because it s able to output high definition 1080p graphics with 1 gigapixel second processing power The onboard GPU can do Blu ray quality playback using OpenGL and OpenVG libraries supplied on chip www allitebooks com CHAPTER 1 INTRODUCING THE RASPBERRY PI The Ethernet and USB Ports The Ethernet and USB ports on the model B board anyway are both supplied via the onboard LAN9512 chip According to the 9512 s dat
67. your pi test sketch and replace it with the following include lt Servo h gt Servo myservo void setup myservo attach 9 Serial begin 9600 223 CHAPTER 14 THE RASPBERRY PI AND THE ARDUINO void loop if Serial available drive Serial read 0 delay 1000 void drive int n if n 5 myservo write 50 else myservo write 250 This code takes the integer you type into your Python prompt translates it to one speed or another based on its value and then writes that value to the servo as a speed To test it hook your servo s power wire to the Arduino s 5V pin the ground wire to the Arduino s GND pin and the signal wire to the Arduino s pin 9 Then save the code upload it to your board and again in your Python prompt experiment with typing different values of ser write 5 from 0 to 9 into the prompt and see how the servo responds Yes it s a very simple code but hopefully you understand the underlying concepts Communicating with the Arduino over the Pi s serial interface is no different from communicating with say a GPS unit or another small breakout chip The Arduino however is not only a bit more intelligent but it is also infinitely more expandable allowing you to add as many additional parts as the Pi does if not more The Arduino and the Gertboard You may be wondering since I ve already discussed using the Gertboard with the Pi how to
68. your script by typing python test py You should be rewarded with the number 6 Congratulations You ve just written saved and run your first Python script 38 www allitebooks com CHAPTER 3 INTRODUCING PYTHON When you write the scripts in this book feel free to use any text editor you wish If you re comfortable using Leafpad by all means use it I tend to use nano or emacs the terminal based editors because I often log in to my Pi remotely and Leafpad can t be run in a remote login session For that reason I ll tell you to edit a file like so sudo nano spam and eggs py but use whichever editor you wish Next let s look at each data type briefly and see what you can do with each Exploring Python s Data Types As mentioned earlier Python provides you with several built in data types In the following sections you ll learn about Numbers Strings Lists Dictionaries Tuples and Files Numbers Numbers seem self explanatory and indeed if you have any programming experience you ll recognize Python s number types integers shorts longs floats and others Python has expression operators that allow you to perform calculations on those numbers these include and comparison operators such as gt gt and or and and and many others All of these operators are built in but you can import others by using another of Python s great characteristics importing modules Modules are ext
69. 0 depends on which Pi model you have Although it s most likely that the board you have uses the 0 try the 1 if you re having no luck reading the bus Tip If you have trouble getting results and you re positive you hooked up all the wires and devices correctly check that all your wires are intact have lost hours and hours troubleshooting a build only to find that one or more of the cheap jumper wires was using was broken inside the insulation meaning wasn t getting signals where was supposed to It happens more often than you think 181 CHAPTER 12 THE SUBMERSIBLE Reading from the Nunchuk You re now ready to read from the nunchuk Eventually of course we re going to translate signals from the nunchuk into commands for the motors but it might be instructional to see what signals we re getting to begin with To do this let s create a Python script that imports the correct modules listens for signals from the nunchuk and outputs them to the screen There are seven signals sent over the wire the X and Y position of the joystick the state of the Z and C buttons on the front and the X Y and Z state of the nunchuk s built in accelerometer We won t use all of these for the sub but we can still take a look at them Here s the full script for you to type in import necessary modules import smbus import time bus smbus SMBus 0 or smbus SMBus 1 if you had to use y 1 in the i2cdetect comma
70. 11 IN3 13 enableB 15 IN4 GPIO setup 11 GPIO OUT GPIO setup 13 GPIO OUT GPIO setup 15 GPIO OUT right motor 19 IN1 21 enableA 23 IN2 GPIO setup 19 GPIO OUT GPIO setup 21 GPIO OUT GPIO setup 23 GPIO OUT enable both motors GPIO output 13 1 GPIO output 21 1 setup nunchuk read bus smbus SMBus O or a 1 if you needed used y 1 in the i2cdetect command bus write byte data 0x52 0x40 0x00 time sleep 0 5 x 1 while True try bus write_byte 0x52 0x00 time sleep 0 1 data0 bus read_byte 0x52 190 data1 bus read byte 0x52 data2 bus read byte 0x52 data3 bus read byte 0x52 data4 bus read byte 0x52 data5 bus read byte 0x52 joy x datao joy y data1 accel x data2 lt lt 2 datas amp oxoc gt gt 2 accel y data3 lt lt 2 datas amp 0x30 gt gt 4 accel z data4 lt lt 2 datas5 amp OxcO gt gt 6 buttons data5 amp 0x03 button_c buttons 1 or buttons 2 button_z buttons 0 or buttons 2 if joy_x gt 200 joystick right go right elif joy x 35 joystick left go left elif joy y gt 200 joystick forward go_forward elif joy y lt 35 joystick back go backward elif button c True X x1 take stillpic x elif button z True print button z n else joystick at neutral no buttons GPIO output 19 0 GPIO output 23 0 GPIO output 11 O GPI
71. 13 Figure 4 13 Breadboarding gone horribly wrong Yes you ll be debugging that conglomeration of wires and no I can t help you But I feel for you I truly do 60 CHAPTER 4 ELECTRONICS AT 100 MPH Power Strip You ll need a power strip but it doesn t have to be anything elaborate It s just a good idea to have all of your electronics desk lamp soldering iron Pi and so on plugged into one source so that you have a failsafe way to abort if you need to One flip of a switch and everything goes off Get one with a surge protector built in if you can Soldering Iron Another critical tool on your list should be a soldering iron and this is the one item you shouldn t skimp on when it comes to cost The 9 99 iron you can get at your local department store might be all right for tinkering with some circuits around the house but when you re a serious builder hobbyist you need a good quality adjustable soldering iron I have a Weller WES51 shown in Figure 4 14 Figure 4 14 Soldering station It s easily the best 100 I ever spent in my electronics career Get one with a stand adjustable heat and tips you can swap Trust me your projects will thank you when you can use the correct temperature to make the solder melt without melting your circuit or when you can use even heat to remove a bad solder joint While you re shopping for the iron get a few soldering accessories as well A solder sucker a hand held vacuu
72. 15 GPIO OUT GPIO setup 19 GPIO OUT GPIO setup 21 GPIO OUT GPIO setup 23 GPIO OUT bus smbus SMBus 0 bus write byte data 0x52 0x40 0x00 time sleep 0 1 while True try bus write byte 0x52 0x00 time sleep 0 1 data0 bus read byte 0x52 data1 bus read byte 0x52 data2 bus read byte 0x52 data3 bus read byte 0x52 data4 bus read byte 0x52 data5 bus read byte 0x52 joy x datao joy y data1 183 CHAPTER 12 THE SUBMERSIBLE the following lines add the necessary values to make the received 5 byte strings easier to decode and 184 accel x accel y accel z buttons button_c button z print Jx 4s Jy Xs Ax As Ay s Az s Bc s Bz As joy x joy y accel x accel y accel z button c button z if joy x GPIO GPIO GPIO GPIO GPIO GPIO elif joy GPIO GPIO GPIO GPIO GPIO GPIO elif joy GPIO GPIO GPIO GPIO GPIO GPIO elif joy GPIO GPIO GPIO GPIO GPIO GPIO elif butt GPIO GPIO GPIO GPIO GPIO GPIO elif butt GPIO GPIO GPIO GPIO GPIO GPIO data2 2 data3 2 data4 2 data5 amp 0x03 buttons buttons gt 200 output output output output output output X lt 35 output output output output 11 1 13 0 15 0 19 0 21 0 23 0 11 0 13 1 15 0 19 0 output 21 0 output 23 0 y gt 200 output 11 0 output 1
73. 3 0 output 15 1 output 19 0 output 21 0 output 23 0 y lt 35 output 11 0 output 13 0 output 15 0 output 19 1 output 21 0 output 23 0 on_c True output 11 0 output 13 0 output 15 0 output 19 0 output 21 1 output 23 0 on z True output 11 0 output 13 0 output 15 0 output 19 0 output 21 0 output 23 1 print data5 amp oxoc gt gt 2 data5 amp 0x30 gt gt 4 data5 amp OxcO gt gt 6 1 2 CHAPTER 12 THE SUBMERSIBLE else GPIO output 11 0 GPIO output 13 0 GPIO output 15 0 GPIO output 19 0 GPIO output 21 0 GPIO output 23 0 except IOError as e print e VU eeee 9 SE 9 9 9 9 9 9 9 eee veccovc9999 owl ip ee eee eee 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 6 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 o Figure 12 6 LED test setup As mentioned earlier the code first creates a bus over which all communications will be made with the nunchuk It then begins communication by writing to the nunchuk s I2C address bus write byte data It then enters a loop where it continuously reads the 5 byte strings coming from the nunchuk data0 datal and so on and categorizes them as joystick directions accelerometer readings and button presses in that or
74. 5 of the time These directions are applicable to standard not continuous servos The difference is that while standard servos use the length of the pulse to determine their final position in degrees from center continuous servos use the length of the pulse to determine the speed at which they should turn A standard servo will move to its destination position and then stop until a new command is sent a continuous servo is almost always moving with the speed of the movement determined by the pulse lengths And while you could conceivably use either type of servo for the cat toy it makes more sense to use standard servos and thus have both the capability of exact positioning and the ability to stop completely allowing the cat to temporarily at least catch the little red dot The problem with this method of moving servos however is that it can be difficult to use the Pi and Python to send millisecond length pulses to the GPIO pins Like all other processes running on the Pi Python is constantly being interrupted by system level running processes making precise timing of pulses by a Python program impractical to say the least However once again the GPIO library has what we need you can use the library to set a GPIO pin as a PWM pin giving it the duty cycle necessary to send the correct length pulses to the pin So while it is theoretically possible to script something like this while True GPIO output 11 1 time sleep 0 0015
75. E4 56YT media Media ntfs 3g auto user rw exec 0 0 The first entry is your drive s UUID the second is the folder we created earlier which will become the mount point the third is the volume type and the last three are the necessary permissions and default options Once you ve added to and saved your fstab file mount all of the drives in it by typing sudo mount a which should force mount all drives listed in fstab if they re not mounted already and you should hear your external drive spin up Then see if it mounted correctly to the correct folder by typing the following which lists all currently mounted drives df h If everything shows up correctly you can move to the next step in the process installing Samba 103 CHAPTER 7 THE MEDIA SERVER Installing Samba As Samba s web site explains Samba runs on Unix platforms but speaks to Windows clients like a native It allows a Unix system to move into a Windows Network Neighborhood without causing a stir Windows users can happily access file and print services without knowing or caring that those services are being offered by a Unix host The name Samba comes from the SMB Server Message Block protocol which is a part of the CIFS Common Internet File System put out by Microsoft in its attempt to get along with other operating systems without causing an outright mutiny This program then is what we need to install on the Pi so that your collection of Windows bo
76. GERTBOARD CUR Re RE E do mTITITITITITUTUTLT 2222323733241 p 222221111 PFFIFETFTYYTYTYYTY Figure 13 4 The converters A digital to analog converter is useful for converting digital signals to a form used by analog devices for example many modern audio signals are stored as digital MP3 files and must be converted to an analog form in order to be played through speakers Digital video signals must be converted in order to be played on an analog monitor An enterprising Pi user might want to output his or her digital signals to an analog device and these pins make it possible On the other hand analog to digital conversion is also very handy when interfacing a digital computer to an analog world and the converter on the Gertboard can be used for that as well For example you may want to read the values from an analog pressure sensor hooked to a hydraulic pressure line Those values are analog values but the Pi s GPIO pins read only digital input You must use a chip to convert those analog values to a digital HIGH or digital LOW so that the Pi can understand them I O Section The I O section of the board is entirely used for buffered inputs and outputs including switches buttons and LEDs See Figure 13 5 In addition to the top row of headers it consists of a row of 12 small surface mounted LEDs three push button switches and three SN74HC244N chips These chips are buffers and they re used to prevent damage to yo
77. In addition make sure you have on hand a regular standard sized screwdriver and a Phillips 42 because you re apt to be assembling disassembling ordinary sized items as well as miniature ones I suggest you get a ratcheting screwdriver with a set of different bits and you ll be prepared for most if not all of your projects Pliers and Wire Strippers Again spend the money on good pliers and wire strippers because you get what you pay for You will definitely need a good pair of needle nosed pliers shown in Figure 4 3 that can be used as tweezers or to bend parts to fit T Figure 4 3 Needle nosed pliers You can probably get away without a regular pair of pliers though I wouldn t recommend it Take good care of your pliers and they ll take good care of you It s difficult to bend wire or cut contacts with a pair of pliers that have gaps in them or don t close correctly You ll also need some wire strippers Yes you can use the cutters attached to your pliers to carefully score wire insulation and strip it but when you have to do that repeatedly every time you need a wire end it gets tedious really fast Get some wire strippers and save yourself the headache Either the kind shown in Figure 4 4 or the kind shown in Figure 4 5 will work just be sure you know how to use them 54 CHAPTER 4 ELECTRONICS AT 100 MPH Figure 4 4 Wire strippers version 1 Figure 4 5 Wire strippers version 2 I actually use both becaus
78. Long degrees longitude str curlat degrees latitude f close subprocess call text2wave position txt o position wav shell True subprocess call ffmpeg i position wav y ar 22050 position wav shell True subprocess call sudo pifm position wav 103 5 22050 shell True subprocess call raspistill o home pi Documents balloon image str picnum jpg shell True 171 CHAPTER 11 THE WEATHER BALLOON picnum picnum 1 time sleep 15 except KeyboardInterrupt SystemExit gpsp running False gpsp join Summary In this chapter you programmed your Pi to get its location from a GPS module and transmit its location to you so that you could stay on the ground and send it into the upper atmosphere to take pictures You worked with threads again as well as a bit more with object oriented code and got a few good pictures from on high I hope In the next chapter we ll go in the opposite direction and send the Pi underwater 172 CHAPTER 12 The Submersible Submersibles both remotely operated and autonomous have been used for both scientific research purposes and private enterprise for several decades They have studied life on the barren intercontinental plains have explored volcanic vents in the middle of the Atlantic Ocean and have gone places impossible for humans to go In the commercial world they were thrust into the spotlight during the Deepwater Horizon
79. O output 15 0 except IOError as e print e Constructing the Sub At this point we re ready to start building the actual submersible Gather your parts together the PVC pipes and elbows waterproof container glues screws and the rest Remember that the design I illustrate in the following sections is just that an illustration not a step by step instruction sheet As long as you end up with a frame of some sort upon which you can mount your waterproofed Pi enclosure and waterproofed motors and propellers you will have succeeded in this task CHAPTER 12 THE SUBMERSIBLE 191 CHAPTER 12 THE SUBMERSIBLE Note Construction plans particularly motor waterproofing procedures have been influenced heavily by the Seaperch program http www seaperch org a program designed to teach students of all ages about building a remote controlled submersible and that encourages involvement in engineering and mathematical fields It is a valuable program and highly endorse its goals Building the Frame Using the PVC pipe and 90 elbows construct a roughly square frame large enough to hold your Pi enclosure After using PVC glue or screws to fasten everything in place cut the plastic netting to fit the square and use the zip ties to fasten it to the frame You should end up with a plastic tray like the one in Figure 12 9 oN X a TN UN je Figure 12 9 The sub platform This is your sub s body I ve left it
80. Only noobs log in as root in other words only neophytes log in and stay logged in as the root user There is a shortcut for logging in as a root user however sudo sudo stands for super user do and it simply tells the system to execute the command as if you were the root user The system will ask for the root password and then execute the command Again the system does not double check with you to see if you really want to do that so when you re using sudo be doubly careful you know the result of the command you just typed before you press Enter 17 www allitebooks com CHAPTER 2 LINUX BY THE SEAT OF YOUR PANTS Commands To get around in the Linux CLI you navigate through the file system using commands such as cd and 1s Commands to run programs are run from the terminal as well Common commands you ll be using on a regular basis and should learn are included in Table 2 1 Table 2 1 Common Linux Commands Command Meaning ls list files in current directory cd change directory pwd print working directory rm filename remove filename mkdir directoryname make directory with directoryname rmdir directoryname remove empty directory cat textfile mv oldfile newfile cp oldfile newfile man command display contents of textfile in the terminal move rename oldfile to neufile copy oldfile to newfile display manual of command date read system date time echo echo what is typed back in the terminal grep search
81. OtherFiles myfile2 txt myfile txt will be gone from your current directory while a copy of it named myfile2 txt will appear in the MyOtherFiles folder on your desktop cp is similar to mv but it copies rather than renames so you don t lose the original file Again you can specify directory levels so cp is handy for copying across folders For example typing cp myfile txt myfile txt places a copy of myfile txt on your desktop assuming you were still in the Desktop MyFiles directory e cat Using cat is a fast way to preview a file like a text file without actually opening it in a text editor Typing cat filename will show you the contents of the file in your terminal even if it s nota text file Try performing cat on an image file and you ll see a bunch of gibberish If you want to preview the file line by line rather than outputting the entire file at once into your terminal use the more command This will fill the screen with the first batch of text and pressing the Enter key will advance through the file one line at a time e date Using date without an argument simply prints the system s date and time to the terminal With an argument it allows you to set that date and time e echo This command merely echoes what you type back to you in the terminal This is not a terribly useful command in the terminal but when you write shell scripts prescripted sets of commands that are run in the terminal it is similar to a c
82. PIO setup 13 GPIO IN pull up down GPIO PUD DOWN pin 15 limit switch GPIO setup 15 GPIO IN pull up down GPIO PUD DOWN pin 19 pressure switch GPIO setup 19 GPIO IN pull up down GPIO PUD DOWN def take pic sensor call raspistill o image sensor jpg shell True time sleep 0 5 wait 1 2 second for pic to be taken before continuing def send text details HOST smtp gmail com SUBJECT Break in TO XXXXXXXXxXx txt att net FROM pythongmydomain com text details BODY string join From As FROM To s TO Subject s SUBJECT text r n S smtplib SMTP smtp gmail com 587 s set debuglevel 1 s ehlo s starttls s login username gmail com mypassword s sendmail FROM TO BODY s quit def motion callback channel global time stamp time now time time 125 CHAPTER 8 THE HOME SECURITY SYSTEM if time_now time_stamp gt 0 3 check for debouncing print Motion detector detected send text Motion detector take pic motion time stamp time now def limit callback channel global time stamp time now time time if time now time stamp gt 0 3 check for debouncing print Limit switch pressed send text Limit switch take pic limit time stamp time now def magnet callback channel global time stamp time now time time if time now time stamp gt 0 3 check for debouncing print Magnetic senso
83. R 3 INTRODUCING PYTHON Like lists dictionaries can be nested gt gt gt dict2 food ham 1 eggs 2 The means the key food has an associated key value of ham 1 eggs 2 which is itself a dictionary Dictionaries have certain method calls specific to them dict keys food drink This lists all of the keys in dict gt gt gt dict has key food True This returns True if dict contains the key food and returns False otherwise Dictionaries can be changed in place gt gt gt dict food eggs dict food eggs drink beer This changes the key value of food from spam to eggs Here you ll notice that eggs aside from being a normal item is also a one item list Note Keys do not always need to be strings as you ve seen here You can use any immutable objects as keys if you happen to use integers the dictionary behaves more like a list that is is indexable by integer key Tuples and Files The last major data types I ll mention here are tuples and files Tuples are collections of other objects that cannot be changed and files refer to the interface to file objects on your computer Tuples are ordered collections of objects They are very much like lists but unlike lists they can t be changed in place and are written with parentheses not square brackets like this gt gt gt t 0 words 23 1 2 3 Here t contain
84. URLopener retrieve and download the file So open your copy of webbot py again and replace the for block of code with the following for link in soup find all a linkText str link if filetype in linkText download file code here You ll notice two elements in this little snippet of code First the str link bit has been added Beautiful Soup finds each link in the page for us but it returns it as a link object which is sort of meaningless to non Soup code We need to convert it to a string in order to work with it and do all of our crafty manipulations That s what calling the str method does In fact Beautiful Soup provides a method to do this for us but learning to parse a string with the str function is important to learn here As a matter of fact that s why we used the line import string at the beginning of our code so we can interact with string objects Second once the link is a string you can see how we can use Python s in call Similar to C s String contains method Python s in call simply searches the string to see if it contains the requested substring So in our case if we re looking for pdf files we can search the link text for that substring pdf If it has it it s a link we re interested in Testing the Bot To make testing our bot easier I set up a page at http www irrelevantcheetah com browserimages htmlto use for testing It contains images files links and various other HTML goodies Usi
85. a sort of sandbox where you can work with Python interactively without having to write whole scripts to see what they do The name IDLE stands for Integrated DeveLopment Environment but it also pays homage to Eric Idle one of the founding members of the British comedy group Monty Python See the sidebar Get Me a Shrubbery Because it s the most user friendly way of trying out code let s use IDLE first Double click the icon on your desktop shown in Figure 3 1 and you should be greeted by a window like Figure 3 2 IDLE Figure 3 1 The IDLE icon 34 CHAPTER 3 INTRODUCING PYTHON Python Shell File Edit Shell Debug Options Windows Ln 4 Col Figure 3 2 The IDLE window To follow the great programming tradition let s start with the first program a programmer ever writes in any language At the prompt type gt gt gt print Hello world and press Enter You should immediately be greeted with Hello world 35 CHAPTER 3 INTRODUCING PYTHON This is Python s print statement whose default output is to the screen Now type gt gt gt X 4 and press Enter The prompt will return but nothing happens What has actually happened is that Python s interpreter has now associated x with 4 If you now type gt gt gt X you ll be greeted with 4 Likewise if you type gt gt gt print x you ll again be greeted with 4 This illustrates another cool aspect of Python dynamic ty
86. ach sensor to your Pi You ll need a small breadboard to place next to the Pi because everything should share a ground Find a good place to mount your Pi where you can plug it in no worrying about batteries and where you can mount the camera so that it can take good pictures of the action Once you ve found a place you can use poster putty to hold everything in place Finally find good places for all of your sensors Remember they don t need to be in sight of the Pi as long as you can run Ethernet cable to them it s a good spot Attach the cables securely and in such a way that nobody trips over them Connect all of the negative wires to your common ground row on your breadboard and connect each positive wire to a GPIO pin At this stage it d probably be a good idea to write down what sensor is attached to which pin so that you can reference it in your code 124 CHAPTER 8 THE HOME SECURITY SYSTEM The Final Code So that completes all the individual parts of this project All that s left is to put them all together in your final code like so you can download the final code file called home_security py at apress com import time import RPi GPIO as GPIO from subprocess import call import string import smtplib GPIO setwarnings False GPIO setmode GPIO BOARD time stamp time time for debouncing set pins pin 11 motion sensor GPIO setup 11 GPIO IN pull up down GPIO PUD DOWN pin 13 magnetic sensor G
87. ack by the electronics you may find a bin full of abandoned power supplies for around a dollar apiece You can either cut off the connector so you can plug it directly into your breadboard or get an adapter like the one in Figure 4 10 58 www allitebooks com CHAPTER 4 ELECTRONICS AT 100 MPH Figure 4 10 Power plug adapter Itend to pick up power supplies whenever I see them or keep them when I throw a device away at home so Ihave a pretty good assortment Try to find at least a 9V and a 12V with different current ratings because these are common voltage sources If your device runs well with your 12V source for example that means it ll probably run well in your car Breadboard A breadboard is another must have when you re putting electronics together to see if everything works as it should You can go full out with a deluxe model with power connections and meters and all sorts of bells and whistles as shown in Figure 4 11 gt Acs Lais sos e Figure 4 11 Prototyping breadboard setup 59 CHAPTER 4 ELECTRONICS AT 100 MPH Or you can go with a more old school version like the one shown in Figure 4 12 Figure 4 12 Analog breadboard Either way just be sure you can plug devices like resistors and ICs into it and that you can connect those devices using jumper wires And as your skills increase and your interests diversify be prepared for your breadboard to someday look like the image in Figure 4
88. ad body p id firstpara align center gt This is paragraph lt b gt one lt b gt lt p id secondpara align blah gt This is paragraph b two b lt html gt soup BeautifulSoup join doc that s two apostrophes one after another not a double quote This loads the file named doc with what a web page stream would look like a long single stream of characters Then soup loads the lines into a file that can be parsed by the library If you were to type print soup at this point it would look the same as the results of typing print doc However if you type print soup prettify you ll be rewarded with the page redone in a more readable fashion This is just an example of what Beautiful Soup can do I ll go over it more when we get to programming the bot 71 CHAPTER 5 THE WEB BOT As an aside the re module you import in the preceding example is used to evaluate regular expressions in text Regular expressions if you re not familiar with them are an extremely versatile way to search through text and pick out strings and sequences of characters in ways that may not be immediately obvious to a human reader A regular expression term can look like complete gibberish a good example of a regular expression is the sequence lt w which searches for a sequence of characters in a string that follows a hyphen To try it out open a Python prompt by typing python and then type import re m re search
89. ahead That is an oversimplification of course but that seems to be the case The BMP180 chip runs on the I2C protocol so you ll have to wire it up to your Pi s SDA and SCL pins pins 3 and 5 like you did with the compass After soldering your headers to the board connect VCC and GND to pins 1 and 6 and then SDA and SCL to pins 3 and 5 respectively 93 CHAPTER 6 THE WEATHER STATION Note You re connecting the chip s power to the Pi s 3 3V notthe 5V You want the chip to run on 3 3V logic so that it doesn t have a chance to damage the Pi s delicate 3 3V inputs To make sure everything is connected correctly run sudo i2cdetect y 0 and make sure the device shows up It should show up as address 0x77 like in Figure 6 10 pi raspberrypi Documents weather pi raspberrypi Documents weather lj Figure 6 10 i2cdetect showing the 0x77 and Oxle addresses in use Note The ox1e device in the screenshot in Figure 6 10 is the connected compass we re using Again this device needs some external libraries to work In this case we ll be using Adafruit s excellent BMP085 libraries Note The BMP180 chip s original version was the BMP085 Although it has since been replaced the schematic and pinout of the chips is the same so all libraries written for the BMP085 also work for the BMP180 To grab the necessary library in your terminal type wget http bit ly NJZOTr no check certificate As we did before
90. an output position This setup is necessary for the buffered outputs to function as outputs rather than inputs If you want to use the pins as inputs the jumpers need to be connected on the bottom row of pins for each IC Once you ve got the pins connected as illustrated you can continue Plug the Pi into your board as shown in Figure 13 1 once you do so various LEDs in the top row should light up showing that everything has power You can now commence with your first program Making Some LEDs Blink Perhaps the easiest introduction to the Gertboard is to do something impressive with the LEDs After all aren t blinking lights one of the reasons you re playing around with electronics in the first place The Python code in the Gertboard user manual was written by Alex Eames of http raspi tv and is basically a translation of the C code To download the Python code for the board to experiment with first make a new directory on your Pi by typing mkdir gertboard and then cd into that directory Once you re there download the zipped programs by typing wget http raspi tv download GB Python zip Then unzip the folder by typing unzip GB Python zip and cd into the resulting folder 210 CHAPTER 13 THE GERTBOARD The first simple script we ll use is the aforementioned leds rg py I ll walk you through this script so open itto follow along and see what it does The first three lines should be familiar to you you re importing time RP
91. an 0 05 seconds after the last one So to test our switch let s hook it up to some GPIO pins and make sure we can read the input when its state changes Just using the switch connect your Pi s power pin 2 to the switch s leftmost pin as shown in Figure 8 7 Then connect the middle pin to your Pi s pin 11 Try the following code by typing import time import RPi GPIO as GPIO GPIO setwarnings False GPIO setmode GPIO BOARD GPIO setup 11 GPIO IN pull up down GPIO PUD DOWN prev input 0 while True input GPIO input 11 if not prev input and input print Button pressed prev input input time sleep 0 05 When you run this script remembering to use sudo pressing the switch will send voltage directly through it from pin 2 to pin 11 thus registering as HIGH at pin 11 It s a debounced signal and the Pi should print Button pressed when you press the button Congratulations You re able to read when a switch is pressed Let s move to the next switch Setting Up the Pressure Switch The pressure switch is very similar to the limit switch though it looks much different See Figure 8 8 Figure 8 8 The pressure switch Rather than a physical lever and button a square pad is used that simply registers pressure as a change in voltage For this reason it s even easier to connect than the limit switch Connect your Pi s pin 42 to one ofthe leads and connect the other lead to pin 11 Then run the sa
92. an HDMI output port To make it easy to program they designed it so that its main programming language would be Python a powerful easy to learn scripting language And thus the Raspberry Pi was born I wrote my first program in BASIC on a Commodore VIC 20 lo these many years ago At 5 KB of RAM it had less computing power than many of today s microcontrollers but I was still able to write a simple maze game on it saving my progress as I went on a cassette tape drive In the years since I ve traversed my way through the different computing platforms from Windows 3 1 to Macintosh OS 8 to a little bit of Linux It had been a long time since I was truly excited by a computer the Pi was a breath of fresh air in a somewhat stale computing environment Not only was it small and cheap but it was easy to get it to interact with the physical world a real boon for anybody interested in designing physical systems So when I heard about its release I signed up like about a trillion other hobbyists hackers engineers and waited impatiently for mine to be delivered Then I started building stuff with it and never looked back If you bought a Pi but aren t sure how to get started with it this book is for you If you bought a Pi but aren t sure what to do with it this book is for you If you re considering buying a Pi but haven t yet because you keep thinking Why should I It s not like I can do anything cool with it right then this book is
93. anager Most package managers have both command line and graphics interfaces Ubuntu for instance uses the Synaptic front end for its aptitude manager 23 CHAPTER 2 LINUX BY THE SEAT OF YOUR PANTS Like Ubuntu the Raspberry Pi uses the aptitude package manager and you ll probably do most of your work with itin the terminal The common command to use to install a piece of software is sudo apt get install package name which instructs the manager to do the following 1 Determine which of its software sources or repositories has the requested file 2 Contactthat repository and determine what dependencies are necessary 3 Download and install those dependencies 4 Download and install the requested software If this seems easy it should it s supposed to be You may run into problems when you request a piece of software not included in your installed repositories but even this is normally an easy fix If this should happen just type sudo add apt repository repository name into your terminal When that s done type sudo apt get update to let your package manager know about the new repository and then type sudo apt get install package name again Luckily the default repositories included in Raspbian hold most of the software you ll ever need so for this book anyway you probably won t run into this problem Text Editors Unlike Windows and Mac which have Notepad Wordpad and Textedit Linux has several possibili
94. ands you can use raspistill to capture pictures and raspivid to capture video Each can be used with various flags and options to change the frame size capture rate and other configurations We re interested in taking still pictures however streaming the video via live feed while possible requires a few extra software tools that can be difficult to set up Taking a picture is a simple call to raspistillfrom the command line And while there is no Python library or module available as of this writing to use the camera we can use the library call from subprocess import callto do the same thing When you need to take a picture in your script use these two simple lines from subprocess import call call raspistill o image jpg shell True A still image labeled image jpg will be stored in the current directory We can put this picture taking line in a take pic function and call it whenever a sensor is tripped We then have evidence should we need it for corroboration Sending a Text Message from the Pi In my opinion having your Pi send you a text message when something unusual happens is one ofthe coolest parts of the project and it s particularly useful if you re going out of town A notification from your Pi can let you know that you need to call your neighbor or the police and have them check on your house It s really pretty simple the Pi uses the local network to send an email message which is then translated by your mobi
95. asheet it s a high speed USB 2 0 hub with a 10 100 Ethernet controller This little chip is only 8 mm to a side but it s capable of 480 Mbps USB 2 0 speeds and fully integrated 10BASE T and 100 BASETX Ethernet support I know this description is a lot of technical gobbledygook but what it means is that almost anything you can plug into your desktop machine can be plugged into your Pi from your router to a webcam to a USB hub to an external hard drive HDD The Audio and RCA Video Jacks Audio and RCA video jacks are also on the board The Pi does support sound over its HDMI output but should you want to plug in headphones it has a standard 3 5 mm audio jack Should you want to use a microphone most USB mics will work assuming they re Linux compatible As for video the Pi doesn t support VGA output but the RCA jack sends video to any connected RCA video device useful if you have a pair of self contained video goggles like the MyVu device The GPIO Pins Perhaps the most overlooked part of the Pi are the GPIO General Purpose Input Output pins These pins allow you to connect the Pi to any number of physical extensions from LEDs and servomotors to motor controllers and extension boards like the large Gertboard which will be introduced and discussed in Chapter 13 With a normal desktop or laptop computer this would require some serious fiddling either with USB drivers or accessing the perhaps nonexistent serial port and doing some serio
96. aw_input Where would you like to start searching n filetype raw_input What file type are you looking for n numSlash start count number of slashes in start need to remove everything after third slash slashList i for i ind in enumerate start if ind list of indices of slashes if len slashList gt 3 if there are 3 or more slashes cut after 3 third slashList 2 base start third base is everything up to third slash else base start br mechanize Browser r br open start html r read linkList empty list of links 79 CHAPTER 5 THE WEB BOT print Parsing start downloadProcess html base filetype linkList for leftover in linkList time sleep 0 1 wait 0 1 seconds to avoid overloading server linkText str leftover get href print Parsing base linkText br mechanize Browser Y br open base linkText html r read linkList downloadProcess html base filetype linkList Summary In this chapter you got a nice introduction to Python by writing a web bot or spider that can traverse the Internet for you and download files you find interesting perhaps even while you sleep You used a function or two constructed and added to a list object and even did some simple string manipulation In the next chapter we ll transition away from the digital world and interact with a very physical phenomenon the weather 80 CHAPTER 6 The W
97. ay not be able to afford ground or flight school a 1 12 scale Piper Cub can go a long way toward making us feel less grounded and we get the chance to fly an actual airplane without having to step foot off terra firma The problem however is that while we can control the plane from the ground it s not quite like actually being there While there are complicated expensive ways of attaching a small video camera to your RC plane it d be nice if you could do something similar with your Pi And it d be really cool if you could keep track of your flight and then load the coordinates into Google Earth to see what your flight looked like Well in this project you can do just that The plan for this project is to put the Pi and a GPS receiver aboard an RC plane and then fly it The Pi s camera will take pictures during the flight and the GPS will log location data Then when you return home you ll use a Python script to parse the location data into a KML file you can upload to Google Earth Note This chapter contains some advanced programming concepts perhaps more advanced than anything you ve come across thus far like threads and even a little bit of object oriented programming OOP But they are not terribly complicated and I ll explain the concepts as they arise A Shopping List of Parts Although this project does not require many parts it might actually be the most expensive project to build in this book because it requires a mediu
98. books may be purchased in bulk for academic corporate or promotional use eBook versions and licenses are also available for most titles For more information reference our Special Bulk Sales eBook Licensing web page at www apress com bulk sales Any source code or other supplementary material referenced by the author in this text is available to readers at www apress com 9781430265627 For detailed information about how to locate your book s source code go to www apress com source code To Becky and Reed Thank you for your patience and support when I disappear for hours days and weeks at a time building all manner of off the wall things and then writing about them Contents ABOUT th AUIBOE scsecsscwacizeucwassveassanadsusvoasesucwasuavueusscvandunsussucaussunsaxasateasuoususscneerseveususseaivouenvad Xv About the Technical Reviewer 1 1n rrree rrr rrr rano annu sanno sua un uasa nanana xvii Acknowledgments J ciis cus eo dcus vEoka ra noe o kan nu VER VERO V dU Rua S EVE ERR SERV KERN RV EEEE UD n PEEEY REC VC xix Higeitiui iu eem Kan aias xxi Chapter 1 Introducing the Raspberry Pi 1 eeeeeeeeeeeeeennnn nnne nnne 1 Tie History of Raspberry PI stc oce e e e e eaten tete utet uetus 2 Exploring Tie PI BOnltl 256 op E S EE DD LL aatet 4 HIE 10 ee eee a AE EE EAE AEEA E AEEA EEA a aE 5 Ingo uum 5 Iro
99. ciated keys and key values is enclosed in curly braces gt gt gt z food spam taste yum Note Keys and key values are an integral part of Python dictionaries They re just linked pairs of values For example in the z dictionary in the preceding code example food and spam are a key and a key value respectively Likewise taste and yum are a key and a key value To use a dictionary you input its key and the associated key value is returned GET ME A SHRUBBERY Python is not named after the snake rather its creator van Rossum named it after the BBC comedy troupe Monty Python of whom he is a huge fan As a result Monty Python references abound in the language The traditional foo and bar used to illustrate code in other programs become spam and eggs in Python examples You ll see references to Brian ni and shrubbery all of which should make perfect sense to you if you are a fan of Monty Python Even the interpreter IDLE is named after M P member Eric Idle If you are not familiar with their work urge you to put down this book and go watch some of their sketches heartily recommend The Dead Parrot Sketch and The Ministry of Silly Walks It s not necessary to be familiar with their work to learn the language but it may help increase your enjoyment of it Running Python Using the Terminal Let s quickly visit another way of using Python which is to use the
100. classic movie 2001 A Space Odyssey If you haven t seen it put this book down and go watch it Now I ll wait Okay so now you can make your Pi speak whatever line you tell it to in the command line While that s pretty cool we need to have it read a line from a text file something like Current altitude 10 000 feet current position 92 degrees latitude 164 degrees latitude The easiest way to do that is to use festival s very handy text2wave function This function reads from a file position txt for example and makes a recording of it Its syntax is text2wave position txt o position wav Now knowing that we ll be updating the position txt file every 15 seconds we can just use the text2wave function to re record its contents before broadcasting that recording using PiFM There s one small snag however text2wave encodes its recordings using a sample rate of 44100 kHz and PiFM needs a recording with a sample rate of 22050 kHz This requires another program for our toolkit ffmpeg Installing FFMPEG In the world of audio and video encoders decoders and transcoders ffmpeg is definitely one of the most popular and powerful programs available It can transcode movie files from MPG to AVI format separate an AVI file into its individual frames and even separate the audio from a film run it through successive filters and re attach it to the video However while all those feats are impressive all we need to use it for is to change
101. cle AUV 173 AUV See Autonomous underwater vehicle AUV B Barometer 93 95 BDFL See Benevolent Dictator For Life BDFL Benevolent Dictator For Life BDFL 33 Breadboard analog breadboard 60 power connections and meters 59 prototype 59 C Cat toy bits connection breadboard 140 completed cat toy 141 final component interconnections 140 PVC pipe 142 soldering wires 141 final code 142 143 GPIO Library Pi 130 pinout 131 voltage 132 laser mechanism completed laser pointer 136 Pi s GPIO pins 135 screw mechanism laser pointer 135 laser to servo connection 136 137 motion sensor see Motion sensor Cat toy ordinary laser pointer 128 parts 127 128 random motion 128 random numbers floating point 129 generation 129 130 Python docs 130 servos see Servos Command line interface CLI 16 Common internet file system CIFS 104 D Digital analogue converters 213 214 227 INDEX E Electronics 9V battery electrocution 52 earth ground 53 electrical equations 52 53 fire extinguishers 63 first aid kit 63 heat 62 ICs 53 inductance 52 lab safety outfit 51 Ohm s Law 52 parts storage organization 64 power 52 Python 51 resistance 53 robotics see Robotics sharp objects 63 soldering techniques 66 veins 52 ventilation 64 water circuit 53 wear Safety glasses 63 F FFMPEG 165 166 G General Purpose Input Output GPIO pins 174 176 Ger
102. click Connect You can now administer your Pi via the command line from anywhere Accessing the GPIO Pins As stated before and as you ve seen if you ve read some of the other chapters in this book the Pi s GPIO pins are the way we interface the Pi with the physical world such as sensors servos motors and lights In order to do this we use a Python library especially designed for this purpose RPi GPIO In order to work with the library you may have to manually install two other libraries It depends on which version of Raspbian you re running First make sure your Pi is up to date by typing sudo apt get update and then install the packages by typing sudo apt get install python dev and sudo apt get install python rpi gpio which may should be already installed Now in order to access the Pi you call import RPi GPIO as GPIO in the first lines of your program and then configure it by typing GPIO setmode GPIO BOARD which lets you identify the pins as they are labeled on a standard pinout diagram as shown in Figure 8 4 116 CHAPTER 8 THE HOME SECURITY SYSTEM GPIOO 5v GPIO4 GPIO14 Ground GPIO15 GPIO17 GPIO18 GPIO21 Ground GPIO22 GPIO23 3v3 GPI024 GPIO10 Ground GPIO9 GPIO25 GPIO11 GPIO8 Ground GPIO7 Revision 1 0 Figure 8 4 The pinout diagram of the Pi s GPIO pins Note Keep in mind that with GPIO setmode BOARD when you refer to pin 77 you re actually referring to the physical p
103. clients to a Windows server as this was a common configuration in a network setup The Windows side however refused to believe that it would ever stoop to receiving files from a Unix server and did nothing to make this easy or even possible However Unix and Linux servers have proliferated even while the number of Windows desktop clients has increased and thus it eventually became necessary for a Windows client to communicate and exchange files with a Unix flavored server While it could be done it was not easy and normally it required a super user with intimate knowledge of networking protocols and languages Enter Samba a program designed to allow these different computers to communicate easily with fewer headaches on the part of the user Configuring Samba Once Samba is installed we need to configure it It s a good idea to make a backup of the current configuration file before you edit it so that you can just restore it should you royally mess it up To do that use Linux s cp command sudo cp etc samba smb conf etc samba smb conf orig 104 CHAPTER 7 THE MEDIA SERVER This command copies the smb conf file to the smb conf orig file in the same directory It needs to be run as sudo because the etc folder can be edited only by the root user When that s done you can open the file for editing by typing sudo nano etc samba smb conf You ll be greeted by a rather large configuration file don t let it scare yo
104. come in very handy Loops Normally a program is executed from top to bottom one line at a time However certain statements can cause the program execution to jump all over the place these control flow statements include if thens and loops The simplest loop is probably a block of code executed a fixed number of times such as for x in range 0 10 print hello 46 CHAPTER 3 INTRODUCING PYTHON This simply prints hello hello hello hello hello hello hello hello hello hello You can also use for loops to iterate through a string or even a list for x in Camelot print Ni Ni Ni Ni Ni Ni Ni Ni or to iterate through and print the characters themselves for x in Camelot print x tO Ho S ur Although the for loop s syntax is a bit different than that of C or Java once you get used to it using the syntax becomes second nature The other loop statement is the while statement This statement evaluates a condition and continues to execute the indented block as long as that statement is true x 0 while x lt 10 print x X X 1 0 1 2 47 CHAPTER 3 INTRODUCING PYTHON WO ON AU HRW Unlike what you may have expected this code never prints 10 because x is incremented after it s printed On the tenth iteration the interpreter prints 9 and then increments x to 10 At this point the while condition is no longer true so the code inside the block is never execu
105. communicating with humidity and pressure sensors that you ll add to the Pi While it s a relatively simple protocol it can get a little confusing so it s best to review it quickly before we start the building the station I2C enables a large number of devices to communicate on one circuit using only three wires a data line a clock line and a ground wire Each device is called a node and there is usually one master node and many slaves Each slave node has a 7 bit address such as 0x77 or 0x43 When the master node needs to communicate with a particular slave it begins by transmitting a start bit followed by the slave s address on the data line That slave responds with an acknowledgment while all other slaves ignore the rest of the message and go back to waiting for the next address pulse to be transmitted The master and slave then communicate with each other often switching between transmitting and receiving modes until all information has been transmitted 82 CHAPTER 6 THE WEATHER STATION I2C has been referred to as the serial protocol on steroids and it is most often used in applications where speed does not matter and the cost of parts needs to remain low The Raspberry Pi has two pins 3 and 5 that are preconfigured to be the I2C protocol s SDA data and SCL clock lines respectively so it can easily communicate with I2C devices Two of the devices we ll be using the barometer altimeter and the magnetometer are I2C de
106. cripting languages are not advances in processor speeds and memory management in today s computers have almost made the speed advantages of compiled languages obsolete A program written to perform a certain task in C and one written in Python may both do so with almost negligible differences in speed Certain tasks may indeed be faster but not all e Yes scripting languages run inside another program However Java is considered a true programming language because it must be compiled when run but it runs inside the Java Virtual Machine on each device This in fact is why Java is so portable the code is transferable as long as a version of the Virtual Machine is running on your specific device C is also a compiled language but it runs inside another programming environment e Okay I can t really argue with the fact that programming languages tend to be more complex and difficult to learn and scripting languages do tend to be easier to read and learn with fewer syntax rules and more English like context Take for example the following two ways to print Hello world to the screen In C you use this include lt iostream gt using namespace std int main cout lt lt Hello world lt lt endl return 0 In Python you use this print Hello world Of course there are exceptions I have seen Python scripts that were almost illegible Likewise there are some very readable C programs floating abou
107. critical problem if your bandwidth and storage are limited Our Web Bot Concept The concept behind our web bot is as follows we ll start with a certain page based on user input Then we ll determine what files we are looking for for example are we looking for pdf files of works in the public domain or freely available mp3s by our favorite bands That choice will be programmed into our bot as well The bot will then start at the beginning page and parse all ofthe text on the page It will look for text contained within a href a tags hyperlinks If that hyperlink ends in a pdf or mp3 or another chosen file type we ll make a call to wget a command line downloading tool to download the file to our local directory If we can t find any links to our chosen file type we ll start following the links that we do find repeating the process for each of those links as recursively as we determine beforehand When we ve gone as far as we want to we should have a directory full of files to be perused at our leisure That is what a web bot is for letting the computer do the busy work while you sip a margarita and wait to enjoy the fruits of its labor 70 CHAPTER 5 THE WEB BOT Parsing Web Pages Parsing refers to the process a computer goes through when it reads a web page At its most basic a web page is nothing more than a data stream consisting of bits and bytes a byte is eight bits that when decoded form n
108. ction As you can see in Figure 6 12 I put all of my chips on a single breadboard and connected it to the Pi so that it was easier for me to mount everything Pi and breadboard on a rotating platform With a decent sized platform on your Lazy Suzan bearing this shouldn t be a problem 95 CHAPTER 6 THE WEATHER STATION Figure 6 12 Breadboarded chips Looking at Figure 6 12 you may have noticed how I wired it I used the power rails running down one side of the board for the positive and negative connections while on the other side I used the rails for the data SDA and clock SCL lines for the I2C connections It s the easiest way I ve found to attach several different I2C devices to the Pi since they share the clock and data lines With the anemometer mounted to your weather station base you can now attach the Pi and the breadboarded compass temperature sensor and barometer chips Because of the short leads from the rotary encoder you may need to mount an additional breadboard to your anemometer mast as you can see in the figure Your finished assembly may look something like Figure 6 13 Power your Pi and you re ready to receive weather updates 96 CHAPTER 6 THE WEATHER STATION Figure 6 13 Completed weather station We ll write the code so that the Pi queries each sensor every 30 seconds and displays the results to the screen See the final code The Final Code The final code is available as weather
109. ctions type help list for an up to date breakdown of everything available Note Python s help function is extremely useful If you don t know how to do something or what s available typing help confusing object at the prompt can aid you immensely See the sidebar Python Help PYTHON HELP If you ever get stuck in Python its online documentation is a very useful resource Point your browser to http docs python org 2 library stdtypes html and you can read about all of the standard data types available to you and how to use them Likewise http docs python org 2 library functions html will show you all of the functions that are always available to you to use Its built in help function is also very thorough To try it in an IDLE session type import string and then help string You ll be rewarded with everything you ever wanted to know about strings Dictionaries Like lists Python dictionaries are extremely flexible collections of objects Dictionaries differ in that unlike lists they are unordered you can access items of a list by their index but items in a dictionary are accessed by key In other words dictionaries contain key value pairs requesting the key will return the value associated with that key For example in the following dictionary the value spam can be accessed by its key food dict food spam drink beer dict food spam 42 CHAPTE
110. d DATA and CLK it d be an understandable mistake to think this board runs on the 12C protocol but it doesn t The pins are just labelled that way In order to work with this sensor you ll have to install the rpiSht1x python library by Luca Nobili Inside your weather directory or wherever you re working on your weather station code download the rpiSht1x library by typing wget http bit ly 1i4z4Lh no check certificate Note You ll need to use the no check certificate flag because I ve shortened the link by using the link shortening service bitly com to make it easier for you to type Ordinarily when you download a file using wget it just saves to your current directory but renaming the link using bitly com can lead to strange behavior when downloading This flag corrects that problem 92 CHAPTER 6 THE WEATHER STATION When it s done downloading which shouldn t take long considering it s only an 8 KB download you ll need to rename it so that you can expand it Rename the downloaded file by typing mv 114z4Lh rpiShtix 1 2 tar gz and then expand the result by typing tar xvzf rpiShtix 1 2 tar gz Then cd into the resulting directory cd rpiShtix 1 2 and run sudo python setup py install You now have the library available to you so let s try it out With your SHT15 still connected as defined earlier type the following code from shtix Shtix import Shtix as SHT1x dataPin 11 clkPin 7 shtix SHTix
111. d holyGrail its radius is holyGrail radius A square named unexplodedScotsman has an area defined by unexplodedScotsman findArea Like I said OOP is beyond the scope of this book Like functions however it can be extremely useful especially in longer more intricate programs Feel free to investigate further as you progress in your Python studies You ll find that Python is a very versatile language as well even allowing you to perform functional and other advanced programming tasks 49 CHAPTER 3 INTRODUCING PYTHON Summary In this chapter I gave you a brief but practical introduction to Python starting with a little of its history and then continuing with how to interact with the Python prompt helping you learn some of its data types and then showing you a little bit of script writing using an editor Don t worry if you can t take all this information in at once there s a lot to learn here and I ll explain what I m doing as we progress through the projects in the book In the next chapter we ll take a look at Electronics 101 You re going to be building projects after all and before you do you should have a basic grasp of the concepts of electricity power and various electronic parts and gizmos 50 CHAPTER 4 Electronics at 100 MPH You bought this book to learn to program using Python and to learn about the Raspberry Pi You also want to build some cool projects learn how the Pi runs Linux and learn how
112. d possibly even doc or docx files You might even want to widen your search parameters to include mobi Kindle and epub files as well as chm These are all legitimate file formats that may contain the text of books you re looking for 73 CHAPTER 5 THE WEB BOT Choosing a Starting Point The next thing you re going to need is a starting point You may be inclined to just say Google but with tens of millions of search results from a simple search for Mark Twain you would probably be better off staying a bit more focused Do a little groundwork beforehand and save yourself and your bot hours of work later If you can find an online archive of Twain s works for example that would be an excellent starting point If you re looking for free music downloads you may want to get a list together of blogs that feature new music files from up and coming bands because many new artists give songs away to download free on those blogs in order to promote themselves and their music Likewise technical documents dealing with IEEE network specifications can probably be found on a technical site or even a government one with much more success than a wide Google search Storing Your Files You may also need a place to store your files depending on the size of your Pi s SD card That card acts as both RAM and a place for file storage so if you re using a 32 GB card you ll have lots of room for pdf files However a 4 GB card may fill u
113. d there is no longer a limit of one per customer There is a buy one give one program in the works in which the Raspberry Pi Foundation plans to donate a Pi to an educational organization for every Pi sold The recent release of the Raspberry Pi camera board a small camera on a chip that plugs directly into the Pi and enables the user to take both still pictures and video promises to open up even more possibilities for this little computer And since the founders actively encourage other companies to copy their paradigm it s anybody s guess what s coming next Exploring the Pi Board So what exactly is on the board It s pretty darn small so what can possibly fit on there There are two models of Pi model A and model B See Figure 1 2 for a look at the model B The two are very similar with model B having a few more features and a slightly higher price than model A Model A has 256 MB of RAM model B has 512 MB Model A has one USB port while model B has two Finally model A has no Ethernet port while the B has one You can still order one or the other model A is 25 US as of this writing while model B is 35 US For the slight difference in price I suggest getting model B The difference between one and two USB ports can be huge and the ability to plug into a hardwired Ethernet cable can make things such as updates and connecting to the board in a small ad hoc network much simpler RASPBERRY PI MODEL B Figure 1 2 The Raspberry Pi
114. d to a device that can spin on an axis like a weather vane so we can determine the wind s direction This is where the Lazy Susan bearing set comes into play First cut two slots in the end of the PVC pipe into which your encoder will fit snugly as shown in Figure 6 5 85 CHAPTER 6 THE WEATHER STATION Figure 6 5 Encoder in slot in PVC pipe Put the PVC cap on the other end of the pipe Attach a light piece of wood to one side of the Lazy Susan bearing and then as near to the middle of the rotation axis as you can attach the PVC pipe and cap with a screw from underneath Figure 6 6 shows one way to determine the center of the axis of rotation Figure 6 6 Determining the platform center When you re done you should have an assembly like the one shown in Figure 6 7 86 CHAPTER 6 THE WEATHER STATION Figure 6 7 Anemometer assembly Connecting the Anemometer to the Pi Now we need to hook up the anemometer to the Pi and measure rotation speeds Connect the red wire of the encoder to the Pi s power pin 2 the black wire to GND 6 and the white wire to a GPIO pin of your choice Let s use pin 8 for illustrative purposes As mentioned earlier this encoder works by sending a HIGH signal every time a slit in the disc passes a certain point We know that there are 90 slits in the disc so every 90 HIGH signals one rotation of the shaft So all we need to do is keep track of the HIGHs and how long it takes to
115. d to run on Intel s x86 based computers In the intervening 20 years it has been ported to every imaginable device from mainframes and supercomputers to tablets televisions and video game consoles The Android operating system is built on the Linux kerneL the nugget of code on which an operating system is built Like most computer software Linux was not born in a black hole It owes its beginning to operating systems and kernels such as Unix BSD GNU and MINIX In fact Torvalds has said on occasion that if the GNU kernel had been complete or if BSD had been available in the early 90s he probably would not have written his own kernel He began his work on the kernel with MINIX and eventually added many GNU software applications He also switched his licensing to the GNU GPL which states that code can be reused as long as it is released under a similar license In the following years Linux spread both in user acceptance and in devices With all of the aforementioned devices running Linux it is the most widely adopted operating system in the world Getting Started with Linux on the Pi To interact with your Pi you re going to be doing a lot of work with the terminal also called the command line interface With your Raspberry Pi desktop up and running double click the terminal icon to start it Because you re already logged in you won t be asked for a user name and password rather the prompt will show something like this pi raspbe
116. d with the introduction of the Pi It has more power than the Arduino the Arduino is only a microcontroller and it has a full ARM processor Of course other options are in the consumer microprocessor board market A popular choice is the Beagleboard an ARM processor based board that also runs different versions of Linux including Angstrom and even Ubuntu Its main drawback is its 100 price tag Parallax puts out a few prosumer grade boards as well such as the eight processor Propeller with a built in breadboard but again it s more similar to the Pi than the Arduino and as of this writing costs 129 Intel s newest entry into the microprocessor market is the Galileo an Arduino compatible development board which also goes for around 100 None of these boards however have gained anywhere near the following of the Arduino An entire culture has sprung up around this popular little board and the incredible things the average person can do with it There are many books web sites forums and groups dedicated to its projects so I won t rehash those sources here However information on interfacing the Arduino with the Raspberry Pi is a bit more scarce The Pi is a Linux based computer and as such is perfectly capable of running the Arduino software In this chapter I ll walk you through installing that software and creating one or two simple projects that run solely on the Pi and the Arduino no desktop machine is required Exploring
117. definitely for you This book isn t meant to be a textbook on Python nor is it an exhaustive exploration of the Raspberry Pi and everything it can do But it is meant to be a fun getting started guide to this neat little computer I hope that after you work your way through the book you ll get a sense of all the things that are possible with the Pi when you combine it with a little ingenuity and creativity on your part If you want to work through the projects here in order feel free If you d rather skip around doing those that interest you you re welcome to do that as well Along the way I hope you ll develop a familiarity with both Python and the Pi that will enable you to continue on building projects as you go and perhaps inspiring others along the way Above all I hope you enjoy the book and its projects It was truly a blast to write Happy computing xxi www allitebooks com CHAPTER 1 Introducing the Raspberry Pi So you ve got yourself a Raspberry Pi mini computer Now what Perhaps you re familiar with the Pi and its architecture but you re wondering what to do with it Perhaps you have some experience with computers but aren t familiar with Linux or Raspbian the Pi s default operating system Perhaps you re already a Linux geek but you don t know how to program in Python and thought it would be a good time to learn Perhaps you have absolutely no experience with computers beyond clicking the Start button checking
118. der The value of those strings indicate what each component of the nunchuk is doing if buttonZ is True for example the button has been pressed Likewise the joystick s Y direction value indicates whether the joystick is being pushed forward or pulled back The long sequence of if elif statements simply iterates through the received values and lights the corresponding LED Running it again using sudo should result in different LEDs lighting depending on what you re doing with the nunchuk As you can see hooking the LEDs in parallel means that they all share a common ground and a common high voltage line In contrast if you were to connect them in series the positive leg of each LED would hook to the negative leg of the next LED with a resistor between the last LED and either the positive or negative pin of the Pi Controlling the Sub Motors and Camera with the Nunchuk Now that you ve got the nunchuk working we need to use it to control the motors of the sub which involves using the L298 motor controller chip Ordinarily we can t drive very powerful motors or servos with the Pi because the Pi can t source supply enough current to drive them To get around this limitation we use a motor controller chip such as the L298 Chips like this called H bridges allow you to hook an external power source to your motors and use the Pi 185 CHAPTER 12 THE SUBMERSIBLE to turn the motors on and off as needed The L298 chip costs only a few
119. des to the software and possibly even the kernel between the time when the Pi Foundation made the NOOBS image available for download and today To update the Pi at the prompt type sudo apt get update You ll see lines of text flow smoothly by as the Pi refreshes its software list When it finishes the prompt will return At this point type sudo apt get upgrade 12 CHAPTER 1 INTRODUCING THE RASPBERRY PI Lines of text should scroll by again If new software is ready to be downloaded the Pi will ask you if you want to download and install it Press Enter the default option When it finishes and returns you to the prompt everything should be at the latest version Depending on what was updated you may be prompted to restart If so reboot restart the desktop by typing startx and you ll be back to the home screen Shutting Down the Pi Before we begin our Linux discussion let s discuss shutdown As a matter of fact shutting down the Pi is unnecessary it s such a low power device that the designers just expect that you ll leave it running You can shut it down though andin the interest of saving a little money and perhaps your Pi I suggest you shut it down when you re done using it Since there s no Off switch the Pi is actually designed to be powered off simply by unplugging it and nothing bad is supposed to happen assuming you ve saved your work aren t in the middle of something and so on But just un
120. dibly informative online blog has a good page with resources on learning how to solder It s located at http makezine com 2006 04 10 how to solder resources Summary After being introduced to some basic electricity principles you learned your way around some of the common electronics tools in the lab and learned the basics of how to use them safely I also introduced you to soldering and pointed you in the direction of some resources to learn to do it better Let s gather our tools and head into the projects starting with a simple one that doesn t require any tools the WebBot 66 CHAPTER 5 The Web Bot As anyone who has spent any time at all online can tell you there is a lot of information available on the Internet According to Google s indexes as of 2013 there are 4 04 billion web pages in existence See Figure 5 1 Sure a lot of those pages are probably cat pictures and pornography but there are also hundreds of millions of pages with information on them Useful information It has been said that every piece of information that has been digitized exists somewhere on the Internet It just has to be found not an easy task when the Internet looks something like Figure 5 1 Internet map Figure 5 1 Visual map of the Internet 2013 http internet map net Ruslan Enikeev 67 CHAPTER 5 THE WEB BOT Unfortunately there s no way any one person could download and read all of the information he or sh
121. do my best to sway your choice away from the swill that is Vim As we discuss programs and scripts throughout the book I won t mention how they re written merely what the end result looks like You may even decide you like the Pi s Leafpad which is perfectly all right as well 24 CHAPTER 2 LINUX BY THE SEAT OF YOUR PANTS Vim vs emacs vs nano Vim is a modal editor It has two modes insert and normal In insert mode your keystrokes become part of the document Normal mode is used to control the editing session For example if you type an i while in normal mode it switches you to insert mode If you then type an i again an i will be placed at the cursor s position exactly as you would expect a text editor to operate By switching back and forth between these two modes you create and edit your document Emacs on the other hand has a more intuitive interface You can move throughout the document using the arrow keys and when you press a key you can expect it to appear wherever the cursor happens to be Special commands like copy paste save and so forth are called by pressing the Control key followed by a sequence of others usually starting with the x So for instance if you wanted to save the current document you would press Ctrl x then Ctrl s highlighted in the emacs menu as C x C s Nano on the other other hand is more intuitive than both of the others You enter text as you would in any other
122. e You ve successfully read the contents of http example com extracted the links there s only one and printed that link to the screen This is an awesome start The next logical step is to instantiate a list of links and add to that list whenever Beautiful Soup finds another link You can then iterate over the list opening each link with another browser object and repeating the process Looking For and Downloading Files Before we instantiate that list of links however there s one more function we need to create the one that actually looks for and downloads files So let s search the code on the page for a file type We should probably go back and ask what sort of file we re looking for by adding the following code line at the beginning of the script after the start line filetype raw input What file type are you looking for Wn 75 CHAPTER 5 THE WEB BOT Note Incase you re wondering the n at the end of the raw input string in both of these cases is a carriage return It doesn t get printed when the line is displayed Rather it sends the cursor to the beginning of the next line to wait for your input It s not necessary it just makes the output look a little prettier Now that we know what we re looking for as we add each link to the list we can check to see if it s a link to a file that we want If we re looking for pdf files for example we can parse the link to see if it ends in pdf If it does we ll call
123. e Tab Tab This shortcut works with commands as well In your terminal type 1 and press the Tab key twice Bash will respond with all available commands that start with 2 It can be a fairly long list You can repeat the process by adding one letter at a time and pressing Tab twice again the shell will fill in all possible commands or files giving you a preview of all possible outcomes Package Managers When you need to install a program from an online source in Windows you normally download an exe or msi file double click it and follow the instructions to install the program Similarly if you re using a Mac you download a dmg file and either copy the extracted file onto your hard drive or use the included installation package Linux however is a little different Linux keeps track of its software using a package management system or package manager The package manager is used to download install upgrade configure and remove programs for the operating system Most package managers maintain an internal database of installed software as well as all dependencies and conflicts to prevent problems when installing software Package managers vary by distribution Debian and the Pi use aptitude while Fedora uses the RPM package manager and Puppy Linux uses PETget If you have experience playing downloaded games you may be familiar with Steam games you may be surprised to learn that Steam s interface is a variant of a package m
124. e although I appreciate being able to choose my wire size in the pair shown in Figure 4 4 I often come across odd sized wire that doesn t fit in any of that model s pre sized holes That s where the strippers shown in Figure 4 5 come into play Wire Cutters You ll need two types of cutters regular cutters Figure 4 6 and fine cutters Figure 4 7 55 CHAPTER 4 ELECTRONICS AT 100 MPH Figure 4 6 Wire cutters Figure 4 7 Fine wire cutters The regular sized cutters are great for everyday work but the smaller cutters are invaluable when you have to snip tiny broken solder joints or the frayed ends of 24 gauge wire Files You won t need anything fancy when it comes to files just a set of small files with varying cuts or roughness The finer cuts can be used for roughening a joint before soldering it or removing a bit of solder from a wire end before inserting it into a breadboard while the rougher cuts can be used to reshape metal and plastic enclosures increase hole sizes and various other tasks Magnifying Light You ll be working with lots of very small objects from resistors to wires to servo connections and your eyes will get tired quickly A good adjustable desk lamp with a magnifier built in is an incredibly valuable investment The one I use is designed for use by jewelers and beaders and the difference it makes when I m trying to work with miniature pieces cannot be overstated See Figure 4 8 56
125. e connect our IR sensor s OUT pin to pin 11 on the Pi and initialize that pin with the preceding line of code everything read on pin 11 will be LOW until movement is detected At that point the pin will read HIGH and we can call the function that turns on the laser and moves it around To test the sensor and our coding prowess we ll start by setting up the GPIO pins accordingly We can use a simple setup to test our code an LED on a breadboard that will light up when the sensor is tripped In a Python script enter and save the following code import RPi GPIO as GPIO import time GPIO setwarnings False eliminates nagging from the library GPIO setmode GPIO BOARD GPIO setup 11 GPIO IN pull up downzGPIO PUD UP GPIO setup 13 GPIO OUT 138 CHAPTER 9 THE CAT TOY while True if GPIO input 11 GPIO output 13 1 else GPIO output 13 O That s it for the test code To test the code and the sensor setup first connect the pin on the sensor to pin 2 on the Pi Connect the OUT pin to pin 11 on the Pi Connect the pin to a common ground line on your breadboard Finally connect pin 13 on the Pi to the positive leg of your LED and connect the negative leg of the LED through a resistor to the common ground line You should end up with something like the configuration you see in Figure 9 9 Figure 9 9 IR sensor and LED test setup Note The image in Figure 9 9 was created with Fritzing http www fritzin
126. e end sudo gpsd dev ttyAMAO F var run gpsd sock Note For more information about the rc 1ocal file see the sidebar in Chapter 10 Now the gpsd module will run every time we start the Pi However we re not done in the rc local file It s likely that when you launch the balloon you ll want to just power the Pi and launch without having to worry about logging in and starting up the program you ve written Luckily you can do that with the rc local file too Upon startup after the gpsd module launches you ll want to give your GPS board a few seconds to get a fix on some satellites before it starts logging data To do that after the gpsd line just shown add the line sleep 45 to make the Pi pause for 45 seconds and then add the line sudo python home pi Documents balloon balloon py Make sure this line matches wherever you re storing your balloon program of course Your balloon program will now start automatically 45 seconds after your GPS module begins to read data from its satellite fixes 166 CHAPTER 11 THE WEATHER BALLOON Using Threading and Objects An important programming feature we ll be using in this project is threads If you already built the RC plane project in Chapter 10 this will be old hat to you If you haven t however here s a quick rundown Threads are important because they allow your program and processor to do several tasks at once and they don t tie up all the memory and processing po
127. e found interesting Human beings just aren t that fast and we have to eat and sleep and perform all sorts of inefficient sometimes unpleasant tasks like showering and working for a living Luckily we can program computers to do some of the boring repetitive tasks that we don t need to perform ourselves This is one of the functions of a web bot we can program the bot to crawl web pages following links and downloading files as it goes It s commonly just called a bot and knowing how to program and use one can be an incredibly useful skill Need the stock reports when you wake up in the morning Have your bot crawl the international indexes and have a spreadsheet waiting for you Need to research all of the passenger manifests for the White Star Line that have been posted online looking for your ancestor Have your bot start with White Star in Google and traverse all of the links from there Or perhaps you want to locate all of Edgar Allan Poe s manuscripts that are currently available in the public domain a bot can help with that as well while you sleep Python is well suited to doing the job of a web bot also called in this context a spider There are a few modules that need to be downloaded and then you can program a fully functional bot to do your bidding starting from whatever page you give it Because traversing web pages and downloading information is not a terribly processor intensive task it is also a task well sui
128. e immediate future Of course the Raspberry Pi is perfect for creating this weather station application A lot of computational power is not required but the ability to easily interact with a small network of sensors is Some are connected to the Pi via I2C Inter Integrated Circuit some are connected via pulse width modulation PWM and some are simply connected to the GPIO pins By simply polling each sensor one by one in a round robin style we can gain an accurate picture of what the weather is doing at any given moment Let s start by gathering the parts required to build our weather station A Shopping List of Parts The weather station does not take a lot of parts but fair warning some of them are a bit more costly than you d think considering their size e Raspberry Pi and power adapter e Digital compass magnetometer https www sparkfun com products 10530 e Optical shaft encoder http www vexrobotics com 276 2156 html e Barometric pressure sensor https www adafruit com products 1603 e Digital thermometer https www adafruit com products 1638 e Small breadboard https www sparkfun com products 9567 e Square shaft from hardware store e Pinwheel or similar fan like device e Lazy Susan bearing e Thin wooden plate e PVC pipe with cap about 12 inches long 1 2 inches in diameter e Miscellaneous jumper wires glue screws Using the 12C Protocol This project takes advantage of the I2C protocol for
129. e that communicating with another board like the Arduino especially via a serial connection is a simple matter and no different than communicating with any other device The main difference of course is that you can program the Arduino using its IDE allowing it to base its actions on information provided to it from the Pi Likewise the Arduino can have sensors hooked up to it act as a sensor network hub and provide information to the Pi This can allow you to offload some of the processing power to the Arduino and free up your Pi for more processor intensive tasks In short the Arduino and the Raspberry Pi don t compete with other they complement each other Each fulfills tasks in a different way and they can be used together to do neat operations in your projects Take some time to acquaint yourself with the interface you ll be glad you did 225 Index A Anemometer assembly 87 connecting to Pi 87 88 encoder slot in PVC pipe 86 encoder with wind vanes 85 platform center 86 square shaft 85 wind speed 84 Arduino 2 Arduino IDE Arduino code 218 Arduino Duemilanove 215 216 blink sketch 221 flash function 223 install pyserial Python library 218 LED 223 loop function 219 myservo 217 pi test sketch 220 221 programming language 215 selection 220 serial port 222 servo 224 setup function 219 sketch 216 217 USB cable 219 void loop function 222 Atmega chip 203 204 Autonomous underwater vehi
130. e value we placed in our Arduino code If you had to use a different port in the connection protocol earlier use that port instead For example you may need to make the second line read ser serial Serial dev ttyACMO 9600 if you had to use the ttyACMO port for your connection Now we can read from the serial device the Arduino which we ve told to transmit once every second Continuing in your Python session type while True ser readline Press Enter twice to finish the while loop and your terminal should immediately fill with text as shown in Figure 14 6 When you get bored watching the Hello Raspberry Pi r n lines populate every second exit the while loop that s running by pressing Ctrl C eoo 1 piGraspberrypi pyserial 2 7 ssh Figure 14 6 Reading from the Arduinos serial port So we ve now established that we can read from the Arduino over the serial connection Let s establish that we can write to it as well Go back to your Arduino pi test sketch and change the void loop function to the following void loop if Serial available flash Serial read 0 222 CHAPTER 14 THE RASPBERRY PI AND THE ARDUINO This code tells the Arduino that if it s able to read from the serial connection to take the first received integer the 0 and send it as a parameter to the flash function which follows here After the loop function enter the following into your sketch void f
131. eSalad jeu wolframdonat d GarageBand n GIMP 81 Documents 5 GitHub Google Chrome SHARED Google Earth M brw0080928 ij Google Sketchup8 fe GoogleAp Launcher Name Google Earth paper 38 GoToMeeting v5 5 Kind Application e rebecca hp 3 Graphics b Size 103 1 MB on disk a d hackin Created 10 7 13 1 47 PM i reed pc 9 Modified 10 7 13 1 47 PM Enable Recommended Applications x Always Open With This application can open plane kml Canes Figure 10 9 Opening plane kml with Google Earth on a Mac When the file is loaded you ll get an image like the one of the parking lot in Figure 10 3 earlier in the chapter The pictures taken by your camera meanwhile will be located in the same folder as your gpstest py file or wherever you specify in your script See the final code at the end of this chapter for an example Here s a final hint Because you put the gps script in your etc rc local file it will continue to start every time you power up until you remove that line from the file If you want to kill the gps script so that it s not running in the background and using processor resources but you haven t gotten around to deleting its line from rc 1ocal type top into a terminal This command shows you all processes currently running on the Pi To stop the Python script look for a process titled python and note the PID Process ID in the first column Press Q to quit top and then type s
132. eady to use the PiFM package To try it out attach a foot long wire to your Pi s pin 7 GPIO pin 4 Now in your terminal type sudo pifm sound wav 100 0 and tune your radio to 100 0 FM You should be rewarded with a familiar tune If by chance you don t hear anything try adding 22050 to the end of the command because that extra parameter the sample rate of the sound file may be necessary to state explicitly depending on the version of software you have Congratulations You ve turned your Pi into a radio transmitter Now let s make it a DJ Installing festival I m pretty sure most of us would love it if our computers would talk to us Luckily since we re using Linux we have a few options when it comes to a good speech synthesizer program The one we ll be using festival is free and very easy to use It also comes with a handy text to speech recording function that we ll be using festivalis available from your standard Pi repositories which means that to use it you only need to type sudo apt get install festival in your terminal and it will download and install Once the download and installation process is complete try it out Plug a pair of headphones into your Pi s 3 5 mm audio out jack Then in your terminal type the following echo I m sorry Dave I m afraid I can t do that festival tts and your Pi will proceed to speak to you In case you don t know that line is spoken by the computer HAL in the
133. eans that because the Pi is both small and powerful it can go places and do things that previously only laptops dared to go and do www allitebooks com CHAPTER 1 INTRODUCING THE RASPBERRY PI Comparing Raspberry Pi to Similar Devices And what you may ask makes the Raspberry Pi better than other small microcomputers like the Arduino and the Beagleboard line of devices The answer to that is that the Pi isn t necessarily better each of these devices fills a particular niche and it can be difficult to compare them Arduinos are awesome for creating simple projects and even controlling a very simple robot In many cases using a Pi to do what you could do with an Arduino would be overkill pure and simple As for the other computers like the Beagleboard the main difference is price A close relative to the Pi is the Beaglebone but the Bone s manufacturer s suggested retail price MSRP is 89 more than twice the Pi s price And purchasing the Raspberry Pi means you re supporting a charitable organization aiming to put cheap computers in the hands of schoolchildren worldwide so there s that too Ithink you would agree that now is as good a time as any to take the Pi out of its box if you haven t already Just read on before you start it up Hardware Requirements of the Pi Let s take a quick look at what the Pi s requirements are and then we ll start it up Connecting to Power Ialready mentioned power the Pi needs 5V no more
134. eather Station Since time immemorial Man has been fascinated by the weather asking questions such as Will it rain for our crops Will it snow so we can go skiing Will a tornado carry our house to a fictitious country populated by supernatural women and flight capable primates We get some kind of weather every day What s it going to be today Forecasting the weather has not always been a scientific pursuit People would pray to the rain gods for rain and to the sun gods for sunshine If prayer didn t work they would often visit a prophet or a seer who professed the ability to look into the future and predict the path of a coming low pressure system though not in those particular words of course Gradually the science behind the weather was discovered and we no longer had to rely on a magical rock for a forecast See Figure 6 1 People attended school to become meteorologists and learn about weather fronts storm surges and other weather related science information Figure 6 1 The weather stone Image 2010 Tom Knapp 81 CHAPTER 6 THE WEATHER STATION Through all of these advances a weather station was needed a small localized way of keeping up on current conditions Even small weather stations normally give wind speed and direction temperature humidity and relative barometric pressure Each of these readings when viewed in combination over the course of a day or two can help you predict the weather for th
135. eceding code this may differ for Yahoo or MSN You can call this function when you detect an input at any of your sensors and you can even adjust the string sent according to which sensor is tripped Implementing the Callback There s one significant idea left to explore in this project and that is the concept of the callback You may have noticed that there s no easy way to check each switch you have to continue to poll each switch and hope that nothing unusual happens while you re doing something else Not a big deal if you have only three or four switches and sensors but should you start adding to your network the delay between something happening and being notified about it can get unwieldy quickly limit switch 2 could get tripped while you re checking magnetic sensor 16 and you won t know about it for another two seconds By that time of course the robber could have snuck by the trip wire and be well on his way to killing your entire family or stealing your Star Wars memorabilia Luckily Python and the Raspberry Pi have an answer to that switch checking problem It s embedded in the RPi GPIO library the threaded callback interrupt What this allows us to do is to start a different program thread for each switch Each thread will go into a waiting mode doing nothing while the rest of the program and the rest of the threads go on about their business If and when the switch gets tripped it immediately issues a callback or interr
136. ect object a new thread newObject myObject and then start it with newObject start The thread is now running with its own instance of the myObject called newObject Our thread as shown in the final code at the end of the chapter will be initiated with threading Thread init__ self Once it has been started it will continue to execute its function in our case collecting GPS data transmitting it and taking pictures until we quit the program or power off the Pi Connecting the Bits The construction of this weather balloon project can be rather involved so set aside a few hours to get everything ready The first thing to do is set up the helium tank When you rent the tank it should come with a regulator and a tilt nipple used to fill balloons This can be used to fill your balloon with one small modification Slip the surgical tubing over the regulator and tape it securely The tubing can then be inserted into the neck of your balloon to fill it as shown in Figure 11 2 and secured with a zip tie 167 CHAPTER 11 THE WEATHER BALLOON Figure 11 2 Regulator to balloon neck setup With the regulator to balloon connection secured you can put together your payload Cut a small hole in the bottom of your Styrofoam cooler large enough to fit the Pi s camera board Fit the camera into the hole securing it with tape if necessary See Figure 11 3 On the bottom of the cooler install the Pi and its battery pack ready to co
137. ed is hot Give it a few seconds to cool before you touch it and see if your joint is solid Wait until your hot glue cools to at least a gel like state before you touch it Speaking from personal experience the worst thing about hot glue is that you can t just shake it off when you get it stuck to your finger Instead it stays right there on your finger and sizzles 62 CHAPTER 4 ELECTRONICS AT 100 MPH Working With Sharp Objects This should go without saying but it s necessary to follow good safety practices when it comes to your cutting tools as well That means e Cut away from your body e Keep your tools sharp Cutting toward yourself even lightly or for a very small cut is simply asking for trouble One slip with an X ACTO knife and you could be committing hara kiri or at the very least heading to the emergency room for stitches Believe me stitches are no fun particularly when the doctor injects an anesthetic into the cut And if you lose a finger completely robotics experimenting will immediately become at least 10 percent more difficult because you will have only nine fingers to work with rather than 10 an immediate 10 percent cut Keep your blades sharp because as any chef knows a dull knife is a dangerous knife If your utility knife blade is getting dull switch it out for a new one Same thing goes for your X ACTO knife blade A dull blade is much more likely to slip and cut you while a sharp knife will simply cu
138. ed to the same folder This is because all of our other devices clients will be looking for that folder when we set them up and we don t want to have to reconfigure them to ask for a different folder every time we boot our Pi To create that folder do it as a root user sudo mkdir media Media 102 CHAPTER 7 THE MEDIA SERVER To set the Media folder as a mount point we need to edit a file called fstab and insert our drive s information First we need our drive s information In your terminal enter the following command sudo blkid This will list all of the drives both virtual and physical currently connected to your Pi The results of my blkid for example look like the screen shown in Figure 7 1 pi raspberrypi media My Book In q y Book fl pi raspberrypi media Figure 7 1 blkid results As you can see the disk mounted as dev sda1 My Book is the one we re interested in and what we need is that disk s UUID Universally Unique Identifier Now we need to open the fstab file by typing sudo nano etc fstab There will probably be a few lines already in the file They follow this format Device name Mount point File system Options Dump options File system check options We need to add our external drive and mount point to the file with the correct file system and options So as an example for a fictitious NTFS formatted drive I would add the following each separated by one tab UUID 39
139. edia Media browseable yes guest ok yes writeable yes public yes available yes create mask 0666 directory mask 0777 This creates the sharing portion of your Samba installation to match the drive and folder we created earlier It also makes the folder browse able and creates the correct sharing permission for that folder 105 CHAPTER 7 THE MEDIA SERVER Setting Linux Permissions Linux file permissions are an interesting beast and they could use some illumination because you re bound to come across them in some fashion in your travels through Raspberry Pi country in the land of Linux Each file or folder has three permission groups associated with it the owner the group and the all users group Those permissions are either r W or x for read write and execute When you list the files in a directory with ls 1 you can see that each item in the directory is preceded by a line like this YWXIWXIWX or drwsr xr x The first character is either a hyphen or a d which tells you that it s either a file or a directory Next the permissions are listed in groups of three in the order of owner group and all users A file listed as rwxrwxrwx means that the owner of the file users belonging to the group that has been assigned to that directory and all users all have read write and execute permissions to that file If the file is listed as rwxr xr x on the other hand it means that only the owner has write pe
140. editor and the commands you use are always shown at the bottom of the screen If you would like to experiment with one or all three of them always a good idea before you make up your mind one way or the other make sure you have all of them installed To do that start by typing sudo apt get install emacs and sudo apt get install vim Vim should be preinstalled on the Pi as is nano emacs however is not Be aware that it s a rather large download so installing it and its dependencies may take a little while Go have a cup of coffee or eat dinner and when you come back it should be waiting for you Using Vim As I said vim is a modal editor meaning that you switch in and out of Insert and Normal modes To start a test file navigate to your desktop and type vim testfile txt Rather than opening another window vim opens in the terminal which can get confusing if you re not used to it You should be faced with a window not unlike the one in Figure 2 4 25 CHAPTER 2 LINUX BY THE SEAT OF YOUR PANTS testfile txt New File Figure 2 4 Blank vim file Vim opens in Normal mode meaning that you cannot edit the file right away To do so you must enter Insert mode by typing i The word INSERT will appear at the bottom left a handy way of reminding you whether you re in Insert or Normal mode When you re done typing press the Esc key to return to Normal mode In Normal mode you can move around the document
141. eir blacklisted status When you re done the file should look like this blacklist spi and i2c by default many users don t need them blacklist spi bcm2708 blacklist i2c bcm2708 180 CHAPTER 12 THE SUBMERSIBLE Save the file and exit You must also add the I2C drivers to the kernel To do this open the etc modules file by typing sudo emacs etc modules and then type i2c bcm2708 i2c dev to the end ofthe file Save and exit Lastly to use the I2C tools you ll need to use sudo apt get to add these few packages sudo apt get install i2c tools sudo apt get install python smbus When those packages are finished installing reboot your Pi Testing the Nunchuk To see if the I2C configuration worked connect your nunchuk to the correct pins 1 3 5 and 6 Start your terminal and enter the following sudo i2cdetect y 0 This queries the I2C bus for the address of all connected devices You should receive a response like this 0 12 3 45 67 8 9 b d e f 00 03 04 05 06 07 DG E Sas RE ee E DOS eiti ote ee We tie Ae ea Seah ee Oa Wate tae Se en mu ae oe i datu he eh ee 40 Oa a Bae E ee tee A ene da tee 10i Be paan E Se Gh ee This shows that the nunchuk is connected at address 52 If you don t see anything and you re certain you ve hooked up the nunchuk wires correctly try running sudo i2cdetect y 1 instead The 1 or
142. elieved to be true and accurate at the date of publication neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made The publisher makes no warranty express or implied with respect to the material contained herein President and Publisher Paul Manning Lead Editor Michelle Lowman Technical Reviewer Chaim Krause Development Editor Anne Marie Walker Editorial Board Steve Anglin Mark Beckner Ewan Buckingham Gary Cornell Louise Corrigan Jim DeWolf Jonathan Gennick Jonathan Hassell Robert Hutchinson Michelle Lowman James Markham Matthew Moodie Jeff Olson Jeffrey Pepper Douglas Pundick Ben Renow Clarke Dominic Shakeshaft Gwenan Spearing Matt Wade Steve Weiss Coordinating Editor Kevin Shea Copy Editor Roger LeBlanc Compositor SPi Global Indexer SPi Global Artist SPi Global Cover Designer Anna Ishchenko Distributed to the book trade worldwide by Springer Science Business Media New York 233 Spring Street 6th Floor New York NY 10013 Phone 1 800 SPRINGER fax 201 348 4505 e mail orders ny springer sbm com or visit www springeronline com Apress Media LLC is a California LLC and the sole member owner is Springer Science Business Media Finance Inc SSBM Finance Inc SSBM Finance Inc is a Delaware corporation For information on translations please e mail rights apress com or visit www apress com Apress and friends of ED
143. en Of Python document which reads as follows e Beautiful is better than ugly e Explicitis better than implicit e Simple is better than complex e Complex is better than complicated e Flat is better than nested e Sparseis better than dense e Readability counts e Special cases aren t special enough to break the rules e Although practicality beats purity e Errors should never pass silently e Unless explicitly silenced e Inthe face of ambiguity refuse the temptation to guess e There should be one and preferably only one obvious way to do it e Although that way may not be obvious at first unless you re Dutch e Nowis better than never e Although never is often better than right now e If the implementation is hard to explain it s a bad idea e If the implementation is easy to explain it may be a good idea e Namespaces are one honking great idea let s do more of those In addition to these commandments Python has a batteries included mindset which means that whatever strange task you need to do in Python chances are good that a module already exists to do just that so you don t have to reinvent the wheel 33 CHAPTER 3 INTRODUCING PYTHON Getting Started with Python Let s get started There are three ways to run Python on your Pi using the built in interpreter IDLE in a terminal window or as a script We ll begin by using IDLE Running Python Using IDLE The IDLE interpreter is
144. en paths It looks similar to an HTML file with opening and closing tags for different levels of information such as Document and Document and coordinates and coordinates Once we ve got the log file from the GPS we need to format the included coordinates in a KML file that Google Earth can recognize Luckily 149 CHAPTER 10 THE RADIO CONTROLLED AIRPLANE this is very easy since we formatted the log file to just have longitude latitude and altitude separated by spaces with format message s and the logging info line Now we can parse each line in the log file separate it by spaces with string split and write it into a preformatted kml file By using the write function we can write each line to the new file called km1 in the script like so kml write Document blah blah blah lt Document gt n Since we know how the final KML file needs to look for Google Earth to use it we can actually write the program that parses the file before our plane ever leaves the ground That way all we need to do is get the data to input from the actuallog file which we ll get when the plane lands The other parts of the file that don t require actual coordinates can be formatted ahead of time For instance every Google Earth compatible KML file begins with the line xml version 1 0 encoding UTF 8 which is then followed by kml xmlns http www opengis net kml 2 2 Document name
145. en to be in when you execute the lines Note however that as written if test txt already exists its contents will be overwritten by the myfile write call If you want to append to the file rather than overwrite it use an a flag when you open it rather than a w Once you have a file open you can read from and write to it bearing in mind that you can only read string objects from file objects This simply means that you must convert all objects in the file to their real data types before you perform any operations on them if myfile readline returns 456 you must convert that 456 to an integer with int if you want to perform calculations on it File operations are very useful because they allow you to create and write to text files but they re a bit beyond the scope of this introductory chapter We ll revisit them later as we use them in projects As you can see Python s built in data types can do anything a true programming language can do sometimes more easily and more economically By combining the types you can do some truly powerful processes with Python as you ll see next Programming with Python Now that you ve seen the data types let s investigate how to use them in actual programs To create a Python program you must exit the interpreter and open a text editor such as emacs or the Pi s Leafpad After you create the program save it with a py extension You ll then be able to run it by typing pyt
146. ence is that this particular GPS board even without the optional antenna is very sensitive When I added the antenna I had no problem getting a GPS signal even in my house Once you know that the GPS unit is working and communicating with the Pi we need to put that information into a format we can use in a log file Although the generic client cgps that we used here is useful for viewing coordinates unfortunately it s really difficult to get usable information from it For this reason we ll use the Python gps module to interact with the receiver Note The gps module allows you to communicate with many different GPS receivers not just the one we re using in this project There are a few receivers that generate proprietary data streams but most of them output the same NMEA formatted data as the chip we re using here Setting Up a Log File When we get the stream from the GPS we need to have a place to store it for later use as it won t do us much good if we re just printing it to a nonconnected screen during the flight What we can do is set up a log file using Python s logging module and then when the Pi is back on the ground we can parse the file and put it into a format we can use in Google Earth Setting up the log file is very simple Start by typing import logging logging basicConfig filename locations log level logging DEBUG format message s These two lines import the module declare the log s file name and wha
147. enough the solder will melt and flow onto the joint The last step is probably the most important The tip of your iron should be clean get in the habit of wiping it on a damp sponge whenever you finish a joint and before you start another one A clean tip will transfer heat better You should also heat the joint not the solder Don t melt the solder onto the tip ofthe iron and then smear it onto the connection you ll run the chance of making a cold solder joint shown in Figure 4 17 which is bound to fail eventually Remember heat the parts not the solder If you have trouble getting the joint hot enough for the solder to melt onto it you can melt a tiny bit of solder onto the tip of your iron before touching a joint since the solder will transfer the heat more effectively You should end up with a joint that looks like the one in Figure 4 18 65 CHAPTER 4 ELECTRONICS AT 100 MPH Figure 4 17 A cold solder joint Note the poor connection Figure 4 18 A good solder joint Again don t stress too much about your soldering skills or lack thereof A little practice and you ll be soldering circuits like an expert Aside from just doing it perhaps the best way to learn to solder well is to watch it and the magic of YouTube now makes that possible A quick search of how to solder brings up over 300 000 results I can t pick any two or three that stand out but if you watch a few you should get the idea Makezine an incre
148. ents are known as assignments where the value on the right is assigned to the variable on the left There are various variable naming conventions in different languages but the best advice I can give you is to just pick a convention and stick with it If you prefer Pascal case ThisIsAVariable use it if you prefer camelback thisIsAVariable use that one Just be consistent you ll thank yourself later In any case an assignment does just that assigns a value to a variable whether that variable is a number string list or something else It s the simplest of the programming functions IF tests The next programming functionality we ll look at is the if statement and its derivatives elif and else Just as you d expect if performs a test and then selects from alternatives based on those test results The most basic if statement looks like this gt gt gt if 1 print true True 1 is the same as the Boolean true so the preceding statement will always print true Note When you type the if statement at the Python prompt in your terminal or IDLE and end it with a colon the next prompt will always be the ellipsis meaning Python is expecting an indented block If you re done with the indented block just press Enter again to end it If you re writing a program in a text editor make sure you indent the blocks you need to indent From here on I ll format the code as if it were in a text editor and print
149. er of fact lists are actually arrays in C inside the Python interpreter As such they can be collections of any other type of object since their contained pointer objects can be pointing to literally any other data type including other lists They are also indexable as fast as indexing a C array They can grow and shrink in place like C and C s lists they can be sliced diced concatenated pretty much anything you do with strings you can do with lists To create a list you declare it with square brackets like so gt gt l 1 2 3 4 5 or gt gt gt shrubbery spam 1 2 3 56 after which you can play all sorts of games with them like concatenating and so on gt gt gt 1 shrubbery 1 2 3 4 5 spam 1 2 3 56 gt gt gt len shrubbery gt gt gt for x in 1 print x 12345 gt gt gt shrubbery 3 41 CHAPTER 3 INTRODUCING PYTHON You may notice here that lists like arrays are indexed starting from 0 By using index and slice operations you can change lists in place as a combination delete and insert gt gt gt cast John Eric Terry Graham Michael gt gt gt cast 0 2 Cleese Idle Gilliam cast Cleese Idle Gilliam Graham Michael Lists also allow you to use function calls that are associated with and specific to them like append sort reverse and pop For an updated list no pun intended of list s fun
150. er purposes such as site testing or to find and download files PDFs mp3s and so on but not to crawl those sites 68 www allitebooks com CHAPTER 5 THE WEB BOT The Connections of the Web Before we get to the business of programming our spider you need to understand a bit about how the Internet operates Yes it s basically a giant computer network but that network follows certain rules and uses certain protocols and we need to utilize those protocols in order to do anything on the web including using a spider Web Communication Protocols HyperText Transfer Protocol HTTP is the format in which most common web traffic is encapsulated A protocol is simply an agreement between two communicating parties in this case computers as to how that communication is to proceed It includes information such as how data is addressed how to determine whether errors have occurred during transmission and how to handle those errors how the information is to travel between the source and destination and how that information is formatted The http in front of most URLs Uniform Resource Locators defines the protocol used to request the page Other common protocols used are TCP IP Transmission Control Protocol Internet Protocol UDP User Datagram Protocol SMTP Simple Mail Transfer Protocol and FTP File Transfer Protocol Which protocol is used depends on factors such as the traffic type the speed of the requests whether the
151. er soldered before your first joints are bound to be lumpy ugly clumps but improvement can be swift if you stick with it No more than a few hours spent soldering components together for practice can make a huge difference when you do it for a real project Soldering basically breaks down to four steps prepare your surfaces tin if necessary connect the parts and heat them 1 Prepare your surfaces If you re connecting wires to other wires or to another surface strip the insulation off of the last half inch or so and twirl the strands together to make a compact bunch Other metal parts may need to be cleaned and if it s a particularly smooth surface roughing it with sandpaper may help the solder stick better to it 2 Tinifnecessary Tinning a surface is simply melting a little solder onto it before you stick it to another surface It s a good practice to get into when attaching wire to an IC leg for instance To tin a wire heat it from the bottom with the soldering iron and hold the solder to the top When the wire gets hot enough the solder will melt right into it 3 Connectthe parts If you can connect the parts mechanically twist wires together wrap wires around an IC leg and so forth If that s not possible that s where your helping hands tool comes into play use it to hold the parts together 4 Heatthe parts With a clean soldering iron tip heat the joint while holding the solder to it When the connection heats up
152. er some thought I decided that the best way to proceed would be to simply start the sub control program automatically when you start up your Pi That way you can turn it on send power to the motors and proceed to work with your sub To do this all we need to do is to edit one file your Cron scheduler The Cron scheduler is a job scheduler you can edit It enables you to schedule tasks and scripts at specified times and intervals To edit it you open the file called the crontab by typing sudo crontab e Each user has its own crontab but by using sudo we ll be editing the root user s Cron which is the user we need to run our Python script You ll see something like Figure 12 8 e00 1 pi raspberrypi ssh GNU nano 2 2 6 File tmp crontab TZWv8L crontab Modified Figure 12 8 The user s crontab file Scroll down to the end ofthe file and enter the following reboot python home pi Desktop submersible sub py amp This is the specific path to your Python script assuming you ve saved sub py in the submersible folder on your Desktop and the amp tells Cron to run the job in the background so as not to interfere with the normal startup routine Save the file by typing Ctrl X Y and then press Return The next time you reboot the Pi sub py will be running test it if you like 188 CHAPTER 12 THE SUBMERSIBLE The Final Control Program We now have all the different Python pieces programmed all that remains
153. er the kernel initializes all devices at startup it goes through the rc files one by one running the scripts contained in each The rc 1ocal file is the last one to run and contains scripts that don t fit in any of the other files For this reason this file is editable by the system administrator and is often used as it is here to keep scripts that need to be run whenever the computer starts An important detail to remember about adding scripts in this file is that because it is not executed as any particular user you must give the script s complete path not merely Documents myscript py for example However that s not all we need to do Before the GPS program will even work we need to turn on the GPS feed again as we did when we were testing the generic GPS client earlier in Connecting the GPS Receiver to the Pi So we need to put that line into etc rc local sudo gpsd dev ttyAMAO F var run gpsd sock Finally we need to wait for the GPS unit to get a fix on some satellites before we start logging otherwise we ll be logging a whole lot of 0 0 0 0 nan coordinates The nan stands for not a number My experience is that it takes about 30 seconds for the unit to get a fix and start returning real data so waiting 45 seconds before starting the script is probably safe To do that just put sleep 45 after the sudo gpsd line you just added and the system will wait 45 seconds before starting the Python script in the next line W
154. ere this picture was not taken with a Pi sub But it could have been If however you live in Alaska the pictures you get may end up looking more like Figure 12 20 and Figure 12 21 199 CHAPTER 12 THE SUBMERSIBLE Figure 12 20 Alaskan underwater photography Figure 12 21 More Alaskan underwater photography These were taken in a lake not far from my house Yes it s pretty boring not much going on in Alaskan lakes in late autumn I ll probably try again in the spring or summer Enjoy your submarine Summary In this chapter you learned about using the I2C protocol to connect a Wii nunchuk to your Pi and use it to control a few different functions on your Pi You then constructed a watertight mobile enclosure for your Pi connected some motors and your camera and were able to remotely pilot your sub and take some hopefully impressive underwater pictures In the next chapter you ll learn how to connect a microcontroller the Arduino to your Pi to increase its capabilities 200 CHAPTER 13 The Gertboard While the Raspberry Pi is an impressive piece of hardware with audio and video interfaces Ethernet USB and GPIO pins it s not all powerful For example it doesn t have an onboard voltage regulator making it possible to easily fry your Pi by giving it too much voltage Nor does it have an easy way to control other circuits such as motors that require more current than the Pi can conveniently s
155. eree 82 Using an Anemometer cccccscessecsessecseessecseesseeseesseeseessesseesueseecsesseeesessaeseessaeeseeeaesseseesseeeaes 84 Building the Anemometer eessssssesesseeseesene nete trente tette ntn inita teint ana ten tnit test sns n atate inen anas 84 Connecting the Anemometer to the Pi sesssssesssseseeseeennen eene tnn tntn tnn tn tn tnra te test tnn 87 Correlating Revolutions per Second with Wind Speed esee eene nennen 88 Connecting the Digital Compass 1 esee rese eren enne rnnt nnn nnns nnn nnn tnnt 90 Connecting the Temperature Humidity Sensor eere 92 Connecting the Barometer 5c e ead d e Dd 93 C nnecting the BIS 555 an os casa teh e teste OH ute n e Lee e e ue REL Eust ode 95 The Final Code E 97 SUMMAY Cos csse a a near eee eee ee SEM ee 100 CONTENTS Chapter 7 The Media Server sssssssnnnunnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn nn 101 A Shopping List of Parts ceto te ete te teet ete ail sete te tl ete etl se tet ete ete ie tete octets 101 USING AN NTFS DING 101 Iristallig Samba eoo opos E EL acne Marae cee EIE 104 win I ES UDTLPCEDIELE M 104 Setting Linux Permissions sisirin 106 Fixing the Apostrophe Bug esssessessesseeseeeene nennen enata tnn tnn
156. erial port or the printer parallel port Both could be accessed with the correct programming libraries sending signals directly to each pin But as technology progressed both ports disappeared and were replaced with USB and Ethernet connectivity As a result it became much more difficult to control external devices from a programming standpoint and this is why many people are excited by the possibilities offered by the Pi s GPIO pins 174 CHAPTER 12 THE SUBMERSIBLE To configure your Pi to access the GPIO pins programmatically you may need to install the correct development kit and tools Just enter sudo apt get install python dev and when that finishes type sudo apt get install python rpi gpio Note python rpi gpio may already be installed depending on your Raspian version Depending on the date you re reading this chapter it may also return an error of Unable to locate package No big deal it s most likely already installed You re now ready to access the pins The Python module used to access them is the RPi GPIO module Itis normally called in the first lines of your program by typing import RPi GPIO as GPIO and then configured by typing GPIO setmode GPIO BOARD which lets you identify the pins as they are labeled on a standard pinout diagram as shown in Figure 12 1 GPIO14 GPIO15 GPIO18 Ground GPIO23 GPIO24 Ground GPIO25 GPIOS8 GPIO7 E C 2 m gt oe GPIO4
157. ert in the pill bottle Figure 12 13 Motor snugly fitted in the bottle 194 CHAPTER 12 THE SUBMERSIBLE Now and here s the waterproofing key stand your pill bottle upright and fill it with wax surrounding the motor and the wires as shown in Figure 12 14 Paraffin wax available from your supermarket works well for this You ll probably have the best luck if you add a small layer of wax let it harden and then continue until the bottle is full Figure 12 14 Motor surrounded by wax When it s securely surrounded by wax make sure your motor shaft can still turn and then slide on the cap fitting the motor shaft through your pre drilled hole Then slide your propeller onto the exposed shaft and you should have a waterproofed motor that resembles Figure 12 15 Repeat for the other motor for the other side of the sub and then fasten the two motors to your sub s frame with zip ties Figure 12 15 Waterproofed motor ready for mounting 195 CHAPTER 12 THE SUBMERSIBLE Connecting the Nunchuck Since we re going to be running Ethernet cable from the sub to your nunchuck which will be kept onboard your boat you ll need to use another length of Ethernet cable Strip the ends grab four wires and solder them to your wiichuck controller Slide the other end of the cable through the top hole in your sub s body and connect the other ends of those four wires to your Pi s GPIO pins Assembling the Final Product Once your
158. es however when you need to make a file executable this is what the chmod command is for but we ll get to that in another chapter such as the chapter dealing with the home media server 1s has some other very useful flags as well ls F lists the current files in the directory but with a after all the contents that are themselves a directory ls a lists all the files including the hidden files those whose names begin with a period or a double period which normally doesn t show in a standard 1s display e cd directory name This command takes you to the directory you named just as you would assume A few special directory names include cd which takes you to your home directory the or tilde signifies your home directory and cd which takes you up one directory in the folder structure In other words if you re in the Desktop MyFiles directory typing cd would place you in the Desktop directory typing cd would place you in your home directory and typing cd MyOtherFiles would take you out of the MyFiles directory on your desktop and put you in the MyOtherFiles directory on your desktop Tip If you simply type cd and press Enter you ll be taken back to your home directory no matter where you are e pwd This is a good command to know When you re lost pwd simply tells you what directory you re in with the answer given as the path from the root directory It is especial
159. essary to put those ideas into practice Whatever your reason for picking up this book your main objective should be to have fun and learn something I ll do what I can to lead the way www allitebooks com CHAPTER 1 INTRODUCING THE RASPBERRY PI The History of Raspberry Pi It may seem to the casual observer that the Raspberry Pi is very new many blog posts still treat it that way and there s a surprisingly huge number of people who have no idea what it is A good number of online articles still begin with something along the lines of The Raspberry Pi is a small credit card sized computer that hobbyists have begun using for This is in stark contrast to say the Arduino most people up on current events have at least heard of the Arduino even if they have no idea what it is or what it s used for because it has been around since 2005 and has gained a loyal and vocal following among hobbyists geeks and do it yourselfers worldwide THE ARDUINO For those who don t know the Arduino is a microcontroller platform mounted on a board that plugs easily into most computers It allows the user to program the onboard Atmega chip to do various things using a C like programming language in programs called sketches A typical Arduino sketch might look like this include Servo h void setup myservo attach 9 void loop myservo write 95 delay 100 myservo write 150 delay 100 This repeatedly moves a
160. et to read input from a voltage source such as a sensor it is what s called a floating input until some voltage is read at the pin Before a voltage signal is sent from the sensor the level at the pin could be almost anything This unspecified floating voltage could seriously screw with your program if you ve programmed the self destruct sequence to activate when the pin reads a 2 3V value and the floating value happens to be at 2 3V BOOM We need a way to set the pin to a known value such as a logical HIGH or a logical LOW when nothing is being read from it 112 CHAPTER 8 THE HOME SECURITY SYSTEM The way to solve this problem is to use a pullup or pulldown resistor This resistor connects the input pin to either Vcc or GND pullup or pulldown respectively That way if there is no input coming in the pin will read either Vcc or 0 and we know that value This is often done with a physical resistor 10KQ or 100KQ normally but many development boards including the Pi will let you do it via software a huge advantage when you re working with limited space Using the GPIO library you can declare a pin as INPUT and at the same time pull it down as if with a pulldown resistor with the following syntax GPIO setup 11 GPIO IN pull up downzGPIO PUD DOWN This defines the value read at pin 11 as LOW until it receives voltage from the sensor at that point that voltage is pulled HIGH and the program can act When the HIGH value d
161. f the window when you re driving down the road you can t upgrade their drivers or use a package manager to download a more efficient gas elimination program The upshot Dogs are great for watching the house but they have some serious shortcomings 111 CHAPTER 8 THE HOME SECURITY SYSTEM Raspberry Pi as Security The Raspberry Pi Rubus strigosus Pi is commonly known as the hobby roboticist s best friend and it has been used to make all kinds of off the wall projects for at least two whole years These devices are descended from the Acorn RISC Machine in the early 1980s and as mentioned previously come in two versions version A and version B The Raspberry Pi does not really have a specific job but as a computer it is well known that it will follow all instructions given it to a fault If you program it to find all prime numbers between 1 and 10 000 it will do so on the other hand if you tell it to continue finding prime numbers until a pig flies overhead it will continue computing until its processor burns out or until Porky grows wings To do these amazing feats the Pi does not have to eat nor does it have to eliminate The trade off for the lack of metabolizing organic substances is that the Pi cannot keep your feet warm on cold winter nights You can upgrade a Pi however with judicious use of the sudo apt get install command The Pi welcomes a USB input and it can be programmed to use sensors to watch your house and its sur
162. ff your Pi now has the ability to truly become an electronic mastermind over whatever collection of circuits you decide to connect to it whether it s your home automation system or your personal 200W CO2 laser powered death ray Jumpers When you purchase a Gertboard it comes with a selection of plastic jumpers shown in Figure 13 8 These are used to make connections between adjacent pins without having to use very short jumper wires a situation that would quickly lead to a chaotic mess on the board given the amount of jumpers that are commonly used Very often their placement determines whether a particular pin is going to function as an input or an output Don t lose these jumpers Most kits sold also come with a few longer jumpers as well If yours didn t don t fret standard female female jumpers work just fine on the board Figure 13 8 The Gertboard jumpers 208 CHAPTER 13 THE GERTBOARD There is one jumper that must in place at all times the power jumper shown in Figure 13 9 Located on the lower right of the board it connects the 3 3V input from the Pi to all the other parts of the board that need power Figure 13 9 The top two pins in this block must be connected by a jumper Now that we ve had a look around the Gertboard let s set up some preliminary jumpers and then do a few simple wiring projects to help you get the hang of using the board and its connections Some Example Projects The Gertb
163. for each connected motor and the ground Motor A is controlled with IN1 IN2 and ENA enable A Motor B is controlled with IN3 IN4 and ENB To control motor A you set ENA to high and then send voltages down either IN1 or IN2 or neither to brake the motor Motor B is controlled the same way The power supply for the motors is connected to the board bypassing the Pi entirely To see an illustration take a look at Table 12 1 and Figure 12 7 Table 12 1 Motor values and settings ENA Value ENA 1 ENA 1 ENA 1 ENA 0 IN1 Value IN1 1 IN1 0 IN1 0 IN2 Value IN2 0 IN2 1 IN2 0 Result Motor A spins Motor A spins Motor A brakes Motor A stops clockwise counter clockwise 186 CHAPTER 12 THE SUBMERSIBLE Figure 12 7 Motors and the motor controller connected to the Pi Obviously all we need to do is set up three GPIO pins for each motor At the same time we read the GPIO pins set as I2C inputs and set the motor pins high or low depending on the signals we re getting from the nunchuk We ll also check for button presses in order to activate the camera Figure 12 7 shows the connections for one motor not both There are no Python libraries available yet to directly interface with the Pi s camera module However fear not we can use Python s subprocess module to make system commands as if we were in the command line If you wanted to take a still picture using the camera from within a Python script you would type fr
164. fset scale bearing math atan2 y out x out if bearing 0 bearing 2 math pi print Bearing math degrees bearing After importing the correct libraries this script sets up functions to read from and write to the sensor s address using the smbus library The functions read byte read word read word 2c andwrite byte are all used to read and write values either single bytes or 8 bit values to the sensor s I2C address The three write byte lines write the values 112 32 and 0 to the sensor to configure it for reading These values are normally listed in the data sheet that comes with an I2C sensor 91 CHAPTER 6 THE WEATHER STATION Note You may have also noticed that very often when you purchase a breakout board from either Adafruit or Sparkfun those companies have example code available for that sensor Check the Documentation link on each site whenever you purchase a part from them As any programmer will tell you if the work has been done already there is no need to reinvent the wheel Nor is there shame in using pre existing code if it solves your problem for you The script then reads the current values of the x and y axis readings of the compass and calculates the sensor s bearing with the math library s atan2 inverse tangent function first converting it to degrees with the library s degrees function The x offset and y offset values however are subject to change depending on your current
165. g org a great open source breadboarding design tool It s cross platform very easy to use and learn and highly recommended When you run the script remembering to execute the code as the superuser or sudo since you re accessing the GPIO pins the LED should light when you move your hand around the sensor and then go out again after a few seconds of nonmovement If it doesn t work check your connections and your parts a burned out LED can cause all sorts of troubleshooting headaches believe me If everything works as planned we can now wire the toy and complete all the connections 139 CHAPTER 9 THE CAT TOY Connecting All the Bits After you successfully test the infrared sensor the code needed to operate it and the code used to work the servos and when everything is attached to everything else it s time to wire everything up and make all the connections This is where a small breadboard comes in handy because you can connect all your grounds together an absolute necessity and run power to everything as needed I used a 9V battery for the two servos but feel free to try different batteries as you prefer It s not necessary to use a rechargeable RC battery in this case as we do in some other projects because weight isn t really an issue and the servos don t run the battery down too fast as they re not constantly running thanks to the sensor However you do need to power the servos with a separate source fro
166. get 90 of them and we ll have rotation speed over time If we track the time in seconds as we will when using the time library we ll have revolutions per second So the code to read our encoder should be something like this import time import RPi GPIO as GPIO GPIO setmode GPIO BOARD GPIO setup 8 GPIO IN pull up down zGPIO PUD DOWN prev input O total 0 current time time 87 CHAPTER 6 THE WEATHER STATION while True input GPIO input 8 if not prev input and input print turning total total 1 prev input input if total 90 print 1 time time current revolutions per sec total 0 current time time Everything interesting here happens in the while loop Since we ve begun by setting the prev input to 0 a 1 HIGH as an input means that the disc is turning In that case we increment total set prev input to input and continue the loop after checking to see if we ve reached 90 HIGHs yet If we have that means we ve gone exactly one revolution so we can calculate and print revolutions per second RPS and reset total and current To test this encoder code connect the wires to your Pi run the script and manually spin the encoder wheel You should see 90 iterations of the word turning and then a line with RPS displayed Correlating Revolutions per Second with Wind Speed If the encoder is working as it should the only step left is to correlate revolutions per second with wi
167. ggies so that you can keep different parts separated but when you pass the point of no return look into storage solutions I have had good luck in the beading section of my local craft store since many resistors and LEDs are about the size of beads My main storage looks like the image in Figure 4 16 Figure 4 16 Organized parts storage 64 CHAPTER 4 ELECTRONICS AT 100 MPH And I have various other plastic boxes and drawers for wheels motors batteries ICs and whatever else I need to store Keeping in that vein you may notice the labels in the picture Buy a label maker Easily another of my best purchases you can label drawers power supplies cords the children the possibilities and uses are endless Keep your area clean Not only is it much more efficient to find things when they re where they re supposed to be but tripping over a power supply cord when holding an X ACTO knife can be a dangerous incident Get your tool or part from its place use it and then put it back This is another area where you may have to do as I say not as I do You ll be seeing pics of my workspace throughout the book and I can t guarantee it ll always be the neatest space I tend to spread out when I work But you get the idea Bonus Soldering Techniques In this last section of this introductory electronics chapter I ll give you a few tips on how to solder Soldering is an art as much as a skill and it does take practice If you ve nev
168. ght of a command line interface gives you the willies If you didn t choose to boot directly to Desktop in the raspi config utility type pi when prompted for your user name and type raspberry for the password to log in to the Pi After that if you want to start a desktop environment type startx at the prompt You shall soon be greeted with a standard desktop complete with a huge picture of a raspberry as shown in Figure 1 6 The icons along the left side of the screen are programs preloaded on the Pi that are used most often Their arrangement may vary from what you see in the image because distributions change and yours is most likely updated from the one I m using as I write this However you ll probably have LXTterminal for command line interfacing Midori the Pi s native web browser the Pi Store IDLE for Python work Debian Reference and maybe one or two others 11 CHAPTER 1 INTRODUCING THE RASPBERRY PI k DLE C Debian feferencs amp Serstch e IDLE 3 e Python Gernes LZ Terroinal Figure 1 6 The home desktop screen on the Raspberry Pi Your Pi is now up and running Congratulations and give yourself a pat on the back Enjoy but don t get too comfy Your next task should be to make sure everything is up to date Most Linux distributions release updates and upgrades regularly and Raspbian is no different There s a good chance there have been several important upgra
169. h faster than card shuffling However computers again are physical systems Yes you re generating the numbers from within the cyberspace of the computer s central processor but that processor is a physical silicon chip with physical transistors and wires No matter what program you use to generate those random numbers they will eventually display a pattern that shows they are not truly random Thus you see the interest in random numbers by mathematicians and scientists A truly random number generator would be incredibly useful in many areas of science not the least of which is cryptography Most ciphers are based on a random hash code a truly random code would be infinitely more difficult to crack which is one of the reasons for the intense interest Current random number generators work by using algorithms that create long strings of pseudo random numbers often based on combinations of multiplications and modulus operations Depending on the quality of the algorithm the numbers thus generated may or may not be cryptographically sound though they are most often random enough for applications such as video games In other words the algorithm you use to generate random numbers probably won t stop a concerted effort to crack the code by a supercomputer but it s good enough to generate opponents when you play Call of Duty The Day We All Died At The Hands Of The Sixth Grader Down The Block 129 CHAPTER 9 THE CAT TOY Th
170. h option has its pros and cons of course but I highly suggest you use a wireless connection This is mainly for two reasons a wireless connection allows you to place the Pi anywhere without having to run Ethernet cable to its location and a wireless connection is also more secure a burglar can cut a wired connection to your Pi to render it useless but not so with a wireless connection The first thing you ll need is a good wireless USB dongle A popular one is the Edimax EW 7811UN shown in Figure 8 1 available on Amazon for only a few dollars It works well is easy to configure and doesn t require a powered USB hub to operate well on the Pi 113 CHAPTER 8 THE HOME SECURITY SYSTEM Figure 8 1 The Edimax wireless adapter Next you ll want to set up your Pi to have a static IP address This will allow you to log in to your Pi remotely from anywhere regardless of whether it has been powered off since your last remote login If you leave the Pi to receive its IP address dynamically from your home router it s possible the IP address will change if the Pi has to reboot meaning you ll be unable to log in because you won t know what the new address is Luckily setting up a static IP for your Pi s wireless connection is not difficult You ll need to know your network s netmask normally either 255 255 255 0 0r 255 255 0 0 and your gateway address normally your router s address such as 192 168 2 1 You ll also need your Bca
171. h you at 50 MPH you have only minutes before the cyclone destroys your house An anemometer can be a fairly complicated device with bearings and shafts and switches and so forth ours on the other hand is relatively simple Building the Anemometer We ll be using a rotary shaft encoder a rotating shaft and some fins to measure the speed of the wind The rotary shaft encoder we re using from Vex robotics consists of a plastic disk with slits spaced evenly around its circumference When power is applied a small light shines through the slits in the disc and onto a photosensitive receptor on the other side By counting the number of times the light is blocked by the disk or alternatively the number of times the light shines through a slit in a given span of time it is possible to determine how fast the disc is spinning It is also possible to determine how many times the disc has rotated and this is in fact how rotary encoders are often used if a rotary encoder is hooked to a robot s axle it s a very good way of measuring how far the wheels connected to that axle have travelled for instance If the disc has 90 slits as ours does we know that one full rotation of the axle one full wheel rotation is 90 flashes of light onto the encoder s photo receptor Thus we can tell the robot Go forward 30 slits and the wheel will advance exactly one third of its circumference forward If we know the circumference of the disc wheel is 3 feet
172. hen you re done your etc rc 1ocal file should end like this sudo gpsd dev ttyAMAO F var run gpsd sock sleep 45 python home pi Documents plane gpstest py Save and exit and the script will now run on startup Connecting the Bits Once you have the plane building this project is relatively easy You ll need a battery for the Pi and a regulator to make sure you re not giving it too much juice I m particularly fond of the Li Po batteries shown in Figure 10 4 that RC enthusiasts use because they re light and pack a lot of power in a small package The ones I use give me 1 3A for an hour much longer than I need 153 CHAPTER 10 THE RADIO CONTROLLED AIRPLANE Figure 10 4 Lithium Polymer li po batteries For the voltage regulator I hacked a USB car charger as shown in Figure 10 5 Figure 10 5 Hacked car charger 154 CHAPTER 10 THE RADIO CONTROLLED AIRPLANE The middle terminal goes to the battery s lead and one of the outer terminals goes to GND Then a simple USB cable gets plugged into the Pi and you have power When it comes to putting everything on the plane it s kind of a hodge podge The important details to remember are to keep the plane balanced and to not disrupt airflow over the wings I put the GPS on the nose and taped the Pi to the wings It s kind of hard to see in the picture in Figure 10 6 but the camera is taped to the port wing pointed at the ground Just behind the wing you can
173. ho has a cat has probably played with a laser pointer with their feline friend at some point But wouldn t it be nice if you could entertain your cat when you re not there A laser pointer contrary to what you might think does not have to be held and controlled by a human A little programming and mechanical engineering magic and you have yourself an autonomous cat toy However in the cat toy project we ll build in this chapter we won t leave it at that We just can t After all it wouldn t make sense to have the toy always moving whether or not your cat is around to play with it would it So we ll add something special an infrared sensor That way it ll turn on only when your cat s around and it will turn off when the cat leaves the room Are you ready Let s start by getting the parts we ll need to create our cat toy A Shopping List of Parts Anice feature of the cat toy aside from being simple and homemade is that the parts are actually pretty inexpensive You will need the following e A Raspberry Pi e Two standard not continuous servos I recommend the Parallax 900 00005 http www parallax com product 900 00005 but any model will work e A cheap laser pointer which you can purchase at a pet store for around 10 US See Figure 9 1 127 CHAPTER 9 THE CAT TOY Figure 9 1 An ordinary laser pointer used with the cat toy e APIR motion sensor http parallax com product 910 28027 e Glue epoxy
174. hon myprogram py Python is unique among programming languages in its syntax in that it blocks out code using whitespace or indentation blocks Languages like C enclose a block of code such as an if statement within curly braces Python uses a colon and indentation to delineate the block Code in C looks like this if x 4 printf x is equal to four Wn printf Nothing more to do here printf The if statement is now over The same code in Python looks like this if x print x is equal to four print Nothing more to do here print The if statement is now over 44 CHAPTER 3 INTRODUCING PYTHON You may notice two additional details about the Python program First the parentheses in the if statement are not necessary In Python parentheses are optional but in most cases it s considered good programming practice to use them as it enhances your code readability You ll also notice that most other languages end their lines of code with a semicolon Python does not This may take some getting used to but itis a nice change to not have a program fail to compile because you ve got a misplaced or missing semicolon somewhere in it In Python the end ofthe line is the end of the statement that simple You ve seen statements already such as X24 y This is a string As mentioned earlier Python doesn t require declarations telling it that x is an integer and y is a string it just knows These statem
175. i GPIO and sys The next line board type sys argv 1 uses a system call to determine what type of board you have the regular Gertboard or the Tandy multiface version This information is then used to print the correct wiring instructions for your board import RPi GPIO as GPIO from time import sleep import sys board type sys argv 1 Note Because you will be following along in the code you just downloaded the entire script is not reprinted here The next section of code checks the Pi s revision number to set the output ports correctly the first revision of the Pi uses port 21 while the second revision uses port 27 The script then creates a list of the ports ports 25 24 23 7 After the list is created we then copy it to ports rev and then reverse it with a call to the reverse method Now we have two lists of ports one numbered sequentially forwards and one numbered backwards The next line simply sets the GPIO mode to BCM The next two lines are an excellent example of Python s for loop syntax They simply run through the list of ports and set them all to outputs for port num in ports GPIO setup port num GPIO out The variable after the for can be named whatever you like the variable after in is the list or dictionary or range or whatever item it is that you re iterating through In this case ports has already been declared as a list and is therefore iterable We then define a method to turn the LEDs
176. iable itself This has the effect of tending to make Python more memory friendly you re not copying entire lists willy nilly and passing them back and forth to functions for example Instead if a function takes a list as a parameter you pass it the memory location ofthe first item of the list and it does what it needs to based on that location and item Another interesting aspect of functions is that they are executable statements This means that a function definition can actually be declared and called within an if statement for example While not normal it s legal and sometimes useful to be able to do this defs can be nested inside loops other defs and even lists and dictionaries We ll visit functions again as we go through the projects for now be aware that they exist and they are extremely useful parts of any program you write Objects and Object Oriented Programming Another important item I want to address in this Python introduction is its native ability to run object oriented code While object oriented programming OOP can be an advanced topic and is probably beyond the scope of this book it s an important enough topic to brush over lightly methinks OOP is a paradigm in which program data is split up into a mix of objects and functions or methods An object is a data type normally a collection of data types like integers strings and so forth Objects are normally part of classes which have associated methods that act o
177. ical or statistical endeavor First of all they are all based on physical systems the flip of a round coin in air the rolling of a more or less square die on a not so level patch of ground Because they are physical systems they can never be truly random Given enough iterations a pattern will eventually start to emerge based on imperfections in the system A coin for example has a slight weight bias on one side due to the patterns engraved on both faces If you flip it enough times that pattern will show itself in the collected results It may take several million or several billion flips but it will emerge Likewise a die will never be perfectly square or perfectly weighted and will eventually show a bias toward one side after a sufficient amount of rolls The second issue with these methods of generating random numbers is simply that they take too much time If you need a good batch of a million random numbers you re going to be flipping a coin for a ong time to get all those numbers It s just impractical for large batches of data But computers are excellent at handling immense batches of numbers and data and they can generate them incredibly fast The average desktop computer can process at a theoretical speed of around 7 Gigaflops That s 7 billion floating point operations per second At that speed generating a million random numbers would take well let s see carry the two divide by yellow um about 7 milliseconds Muc
178. id thread the parachute strings through the hole and secure them to the lid with hot glue Then loosely tie a string around the chute tightly enough to keep the parachute closed upon ascent but loosely enough to allow the chute to break free and open if the cooler begins tumbling in free fall 169 CHAPTER 11 THE WEATHER BALLOON The last things to do are power up the Pi tape the lid tightly onto the cooler and attach it to the filled balloon When the balloon is at its desired volume and this will vary with the weight of your payload so some experimentation is necessary remove it from the tank and tie off the end with either zip ties or rubber bands Then attach the neck of the balloon to your cooler again using zip ties and release it The balloon will float into the atmosphere taking pictures as it goes Meanwhile tune your radio to 103 5 FM or whatever station you set in your final code and listen to the live updates as your balloon tells you exactly how high it is Unless it bursts always a distinct possibility the balloon should travel to the end of the attached fishing line which is a good reason to get as much line as you can in order to allow your balloon to ascend as high as possible When it s time to retrieve your balloon use the attached fishing line to reel it back in To save your arm muscles you may want to attach the fishing line spool to an electric drill Note Check with your local branch of the FAA or it
179. ile2 txt by typing echo This is another file gt file2 txt Now rename your first file to file1 txt by typing mv file txt filei1 txt If you now list the contents of the current directory you ll see file1 txt and file2 txt Next let s copy file1 txt to the directory one level up in the folder structure Type cp filei txt file1 txt Let s move file2 txt to our home directory by typing mv file2 txt file2 txt If you now list the contents of your home directory by typing ls you ll see that file2 txt is there while it has disappeared from your current directory Congratulations You ve now successfully accomplished the most common file operations in the Linux command line or shell Speaking of shells Linux has several available in most distributions Shells in Linux Shells in Linux have names like the Bourne shell the C shell and the Korn shell A shell is simply a text based interface between the user and the operating system allowing the user to execute commands directly to the file system Each shell has its pros and cons but it would be misleading to say that one is better than another They are each simply different ways of doing the same thing The Bourne again shell also referred to as bash was written as a replacement for the Bourne shell and is the default on most Linux flavors including the Pi s Raspbian It can be identified with its login prompt the Bash has some keyboard shortcuts that can become very
180. in 11 which translates to GPIO17 in the diagram in Figure 8 4 not GPIO11 which translates to the physical pin 23 Once you ve set the mode you can then set each pin to be either an input or an output Users of the Arduino will probably recognize the concept here GPIO setup 11 GPIO OUT GPIO setup 13 GPIO IN and so forth Once you ve set a pin as an output you can then send voltage to it turn it on by using GPIO output 11 1 117 CHAPTER 8 THE HOME SECURITY SYSTEM or GPIO output 11 True and subsequently turn it off by using GPIO output 11 O or GPIO output 11 False When you configure a pin as an input remember to set a pullup or pulldown resistor as discussed earlier Setting Up the Motion Sensor One of the most important parts of a home security network is likely the motion sensor shown in Figure 8 5 with a few caveats You can t rely solely on your motion sensor because the moment you do it ll be set off by a neighborhood cat or possibly a Yeti not necessarily a bad thing If however you use it in addition to all other sensors you may have good luck with its results Figure 8 5 The motion sensor The sensor we re using by Parallax or a close clone detects motion by detecting changes in the infrared heat levels emitted by objects in the surrounding environment Like most sensors it then signals that a change has been detected by outputting a HIGH or 1 signal on its outp
181. ing with Beautiful Soup I mentioned parsing earlier Beautiful Soup is still the best way to go If you haven t done so already enter sudo apt get install python bs4 into a terminal and let the package manager do its work It s ready to use immediately afterward As I stated before once you download the page Beautiful Soup is responsible for finding links and passing them to the function we ll use for downloading as well as setting aside those links that will be followed later As a result of this however it turns out that the job of finding links and determining what to download becomes mainly a problem with strings In other words links and the text contained within them are nothing but strings and in our quest to unravel those links and follow them or download them we ll be doing a lot of work with strings work ranging from 1strip removing the leftmost character to append to split and various other methods from the string library Perhaps the most interesting part of a web bot after all isn t the files it downloads rather it s the manipulations you have to do to get there Downloading with the urllib Library The last part of the puzzle here is the urllib library specifically its URLopener retrieve function This function is used to download files smoothly and without fuss We ll pass it the name of our file and let it do its work To use urllib you must first import it Switch to the terminal with your Python prompt
182. int you can poll the pin at any time by typing if GPIO input 11 print Input was HIGH else print Input was LOW Insert this simple piece of code in a loop in your script every time the loop runs the script will check the pin s status We ll use this functionality in our final submersible program to trigger the camera to take pictures Installing the Raspberry Pi Camera Board The submersible we ll build will be equipped to take pictures either at preset intervals or at the press of a button Obviously this means we need to install the camera module that interfaces with the Pi 176 CHAPTER 12 THE SUBMERSIBLE When you get the camera board it will most likely come in a plain white box inside of which is an anti static gray bag containing the camera board Make sure you have discharged any static electricity from your body because the camera is very sensitive to static by touching a good ground and then remove the camera from the bag The camera connects to the strip connector located on the board between the HDMI output and the Ethernet port Open the connector by pulling up on the sides it ll pop up by a few millimeters which is all you need Position the end of the camera s ribbon cable so that the connectors the silver side not the blue side are facing the HDMI port Slide the cable into the connector until it bottoms out to make sure you have a good connection Then while holding the cable still press dow
183. inter casing If you have room drill a small hole in the pointer casing to hold the positive wire Then attach your wires and solder everything Your results may vary depending on your soldering abilities and the materials with which you re working You can even use glue as long as you don t get glue between the metal contacts of the wires and pointer parts It s important that all the wires have a good solid connection The last step is to mount the entire device in some sort of container to hold it all in place and to protect the guts of the machine from feline investigation You can keep all the parts breadboarded as long as it s protected from the end user your cat I tend to use PVC pipes in cases like these because a standard servo fits almost perfectly in a 2 inch I D PVC pipe In this case you can mount the lower servo to the edge of the pipe and most of the wires and guts can be stowed securely inside of it with a hole drilled in the side for the IR sensor The Pi won t fit but it can be safely stowed away in a separate box connected to the pipe assembly via long jumper wires Hopefully you end up with a cat toy that looks something like Figure 9 11 Figure 9 11 Completed cat toy 141 CHAPTER 9 THE CAT TOY It s not pretty but your cat won t care It can be gussied up of course with a cap on the end of the pipe and a coat of paint Probably the most important detail to remember and it s not shown here is to hide
184. interface with the Atmega chip on the Gertboard The Atmega chip after all is the chip used on the Arduino so it stands to reason that you could use the Arduino s IDE to interact with it The answer is that to use the Atmega chip on the Gertboard with the Arduino IDE you need to install quite a bit of extra software and make some changes to the Pi s and the Arduino s configuration files Finally perhaps the most troubling it requires four of your GPIO pins to communicate with the Atmega chip Meanwhile using an external Arduino is quite simple and doesn t require any of your precious GPIO pins to be sacrificed If you want to install the Gertboard software an excellent tutorial and walkthrough is available on Gordon Henderson s web page at http bit ly 1fgEFeo Recall that Gordon is the developer of the WiringPi library I mention in Chapter 13 The Gertboard That library attempts to make it as easy to access the Raspberry Pi s GPIO pins as it is to access the Arduino s pins Gordon has done some incredible work in writing and making available the software necessary to program the Gertboard s Atmega chip and I highly recommend that you take some time to go through his site he does a better job than I ever could of explaining the process 224 CHAPTER 14 THE RASPBERRY PI AND THE ARDUINO Summary Although this chapter has provided just a short introduction to how to interface the Arduino with your Raspberry Pi I hope you now realiz
185. into a motion sensor via its GPIO pins and let you know with a few lines of code whether Slenderman is creeping about in the bushes behind your bedroom In our security system we re going to use several sensors an infrared motion sensor a pressure switch a magnetic sensor and a reed or limit switch The motion sensor can be placed anywhere on the grounds The pressure switch might be useful placed inside a doorway where an intruder is likely to step The magnetic sensor can be used to detect if a window is opened and the reed switch can be used to determine if someone touches a trip wire We can use the Pi s onboard camera to take pictures if any sensors are tripped and access those pics any time Last we can use our home network to have the Pi send us a text message and or email message should something interesting be happening in our security network kind oflike the security company calling you if they detect an alarm This is the sensor network we ll be working with It s kind of basic but it s also infinitely expandable And although we ll just be using one of each kind of sensor you can easily add more if you want to one magnetic sensor for each window in your house for example Understanding a Pulldown Resistor One important concept to know and remember any time you use an input with almost any circuit is that of the floating input and the pulldown or pullup resistor Basically whenever a pin such as a GPIO pin on the Pi is s
186. irectly connected Pi via a standard terminal connection ssh 1 pi 192 168 2 42 and you can work exactly as you would on your home network Connecting the Digital Compass The digital compass we ll use in this project has one purpose to let us know which direction the wind is blowing The one we re using the HMC5883L uses the I2C protocol so make sure you re familiar with the information in the section Using the I2C Protocol earlier in this chapter before you continue Start by soldering the male headers that came with it to the HMC breakout board The orientation is up to you if you plan to make it standalone you may want the headers facing up so that they re easy to access If on the other hand you re planning on plugging the chip into a breadboard by all means solder them facing down so that you can easily plug the whole unit into your board Once the headers are soldered to the board connect the pins to your Pi with jumpers VCC and GND go to the Pi s 2 and 6 pins respectively and SDA and SCL to the Pi s 3 and 5 pins You re now ready to use the smbus library to read from the compass using a little math eek to calculate the bearing based on the sensed x and y values Now would be a good time to use the i2cdetect tool mentioned earlier to make sure you can read from the compass Run the tool by typing sudo i2cdetect y O or1 and you should see the chip listed with address 0x1e See Figure 6 9 pi raspberrypi Documents
187. irements adding monitor 7 adding USB hub 7 8 connection power 7 wireless USB dongle 8 9 Linux based computer 215 OS see Operating system OS Pi prosumer grade boards 215 Python 1 Servo 223 shutdown 13 uses Foundation 3 RC airplane See Radio controlled RC airplane Remote Operated Vehicle ROV 173 Revolutions per Second RPS 88 89 Robotics breadboard 59 60 finer cuts 56 hot glue gun 57 light magnification 56 57 multimeter 57 58 pliers and wire strippers 54 55 power strip 61 power supply 58 59 230 screwdrivers 54 soldering iron 61 62 superglue 57 wire cutters 55 56 ROV See Remote Operated Vehicle ROV S Sensor network home security system bit connection 124 callback 124 definition 112 final code 125 126 GPIO pins 116 118 magnetic sensor 122 motion sensor 118 119 Pi s camera 123 pressure switch 121 pullup pulldown resistor 112 reed switch 120 121 Sending a Text Message Pi 123 124 shopping list of parts 113 wireless network 113 Edimax EW 7811UN 113 114 raspi config tool 114 SSH server 114 116 Wireless network 114 116 Server Message Block SMB 104 Servos changing duty cycle 134 construction bonded X and Y servos 135 pan and tilt servo mechanism 134 duty cycles 133 length pulse 132 Pi and Python 133 pulse width modulation PWM signals 132 standard servo 133 SoC See System on a Chip SoC Soldering iron hands tool 61 vacuum pump 61
188. is generation process is why when you begin a program that will be using random numbers you have to seed the random number generator with another number such as today s date or the system time on your computer The random seed is simply a number used to initialize the random number vector algorithm in the program So long as the original seed is ignored subsequent initializations should provide sufficiently random numbers Yes eventually a pattern will emerge it s inevitable but a randomly seeded generator should be sufficiently random for most needs particularly a random motion cat toy Schr dinger s cat might not be fooled but your feline should be Sorry just a little physics humor there According to the Python docs randint a b returns arandom number n such that n is between a and b inclusive In other words the following code gt gt gt import random gt gt gt x random randint 1 10 print x should return 1 2 3 4 5 6 7 8 9 or 10 We re going to use it to generate positions for the servos we use Note The Python docs can be found at http docs python org highly recommend that as you learn the language you get in the habit of consulting the docs You can also type help function at the interactive Python prompt to get the same reading material Using the GPIO Library Now that you have an idea of how we re going to generate our random numbers you need to know how to control the
189. isappears the pin is again pulled LOW until the process repeats A pullup resistor does almost the same thing except the pin is pulled HIGH to Vcc until an input appears A Shopping List of Parts In order to build a functioning home security system there are a few parts you re going to need e A Raspberry Pi obviously and power adapter e A wireless USB dongle if you want to go wireless with your Pi e Raspberry Pi camera module e Pressure switch such as http bit ly Owc8aN for example e Magnetic sensor such as http bit ly 1cis71c for example e Motion sensor such as http bit 1y 1c35p0p for example e Reed switch such as http bit ly 1k6n2RM for example e Large spool of Ethernet cable crimped ends not required buy in bulk to save money e Solder soldering iron and miscellaneous jumper wires and connectors Some of these parts are optional of course it all depends on how thorough you want your security system to be You can even add items to your list as your security system grows Each sensor merely adds to your sensor network expanding your system s reach Connecting to Your Network Wirelessly When you set up your Pi as the main controller of your security system it will have to connect with your home s network in order to allow you to remotely log in and administer it and to send you a text message to inform you of an infraction When you connect to your network you have the choice of going wired or wireless Eac
190. iting To continue type f write This is a test of my file writing f close If you now exit your Python prompt by pressing Ctrl d and list your directory contents you ll see testfile txt listed and viewing its contents will show you the line you just entered Now try it again start another Python prompt and type f open testfile txt w f write This text should overwrite the first text f close and exit your Python prompt Because you opened the file using a w parameter all the original text was overwritten This is what you ll be doing in our GPS location file We re not interested in saving the locations as we did before rather each location will be recorded and then transmitted and then we can overwrite it with the next location by opening it with the w flag Installing PiFM To get your Pi to talk to you over the radio you ll need to use a handy little hack developed by the fellows at the Imperial College Robotics Society in London The module called PiFM uses the Pi s existing hardware to turn it into a nice little FM transmitter To use the module you ll first have to download it In your balloon directory open a terminal and type wget http omattos com pifm tar gz When it s done downloading extract it by typing tar xvzf pifm tar gz 164 CHAPTER 11 THE WEATHER BALLOON This will place a compiled binary as well as the source code and a few sound files in your directory You re now r
191. ked GND They re all connected after all 3 Connect the negative lead of your LED to the pin marked RLY1 in the J12 header again at the top right of the board 4 Connectthe positive lead after a resistor in series to any pin on the board marked RPWR Press Enter and you ll see the LED blink on and off several times Impressive No not really But it bears repeating the ability to control an external circuit completely independent of the Pi s power source is an important one It allows the Pi to act as a mastermind or puppeteer turning subsystems on or off as required Using the Digital Analogue Converters The Gertboard is equipped with a digital to analogue converter chip from Microchip It s either an 8 10 or 12 bit chip depending on what parts were available when the board was manufactured To determine which one you have closely inspect the chip in U10 See Figure 13 12 213 CHAPTER 13 THE GERTBOARD Figure 13 12 D A converter by Microchip There is a number stamped on the chip either 4802 4812 or 4822 The third digit will tell you if your chip is an 8 10 or 12 bit version Regardless of which chip you have the pinout is the same and the results are the same sending a digital input of HIGH or all 1 s 11111111 1111111111 or 111111111111 depending on your chip version results in a voltage out of 2 04V According to the chip s datasheet the output of the chip can be determined by the f
192. l of this story is that although I used a glass of water I had a fire extinguisher nearby that I was ready to use if I had needed to and so should you They re not expensive and they re well worth the cost when it comes to possibly saving your house or workshop from a fire Get an extinguisher and be sure to keep it charged Also be sure to learn how to use your fire extinguisher before you need it Think of it as being like bear spray as you re hiking in the wilds of Alaska and need to fend off a bear You would definitely practice using it before you go hiking since it can be extremely difficult to read directions while running from an angry grizzly Your fire extinguisher is similar it can be very difficult to read and follow the instructions while your workshop is turning into a remake of The Towering Inferno Become familiar with it and hopefully you will never have to use it Keep a First Aid Kit Handy Although this should go without saying always have a first aid kit nearby You don t need a full Level 1 Emergency Kit that you could take on an Antarctic expedition but a small well stocked kit should be somewhere in close proximity The kit should contain some Band Aids alcohol cotton swabs and maybe a few other odds and endis It s difficult to solder a joint when you re bleeding all over it 63 CHAPTER 4 ELECTRONICS AT 100 MPH Work in a Ventilated Area One important detail to remember when you re working is to keep your
193. l without your help Now that you get the idea you can go crazy with it Create directories surf three and more levels deep and see what your bot downloads for you while you re not looking Half the fun is sometimes seeing what gets downloaded when you least expect it 78 CHAPTER 5 THE WEB BOT The Final Code Here you can see the final lengthy code you ve been typing in bit by bit if you ve been following along as we progressed through the chapter Again if you don t want to type it all it s available on Apress com as webbot py However I highly recommend you type it in because learning code can be much more effective if you type it rather than simply copying and pasting it import mechanize import time from bs4 import BeautifulSoup import re import urllib import string import os def downloadProcess html base filetype linkList This does the actual file downloading soup BeautifulSoup html for link in soup find all a linkText str link get href if filetype in linkText slashList i for i ind in enumerate linkText if in directoryName linkText slashList 0 1 slashList 1 if not os path exists directoryName os makedirs directoryName d image urllib URLopener linkGet base linkText filesave string lstrip linkText image retrieve linkGet filesave elif htm in linkText covers both html and htm linkList append link start http r
194. lash int n 1 for int i 0 i lt n i digitalWrite ledPin HIGH delay 100 digitalWrite ledPin LOW delay 100 This function flashes the Arduino s onboard LED hardwired to its pin 13 n number of times which were passed to it as a parameter As you can see the concept is similar to the GPIO s OUTPUT functionality first you declare the pin to be an output and then write either a HIGH or LOW value to it to turn it on or off Save the sketch again and re upload it to your Arduino board Then go back to your terminal and in the same Python session type ser write 4 and you should be rewarded with the Arduino s onboard LED flashing four times Try it with different numbers and make sure it s working Remember however that the Arduino is set up to read only the first integer sent to it If you type ser write 10 it will flash once not 10 times Congratulations You re now able to read and write to your Arduino from your Raspberry Pi Running a Servo Admittedly flashing an LED on command is not the most impressive operation you can do with your Arduino Pi combination My main goal is to teach you how to get the two devices to communicate and leave the possible uses and implications up to you but let s discuss communicating with a servo connected to your Arduino As a matter of fact all we need to do is modify our LED code just a bit to interface with a servo rather than an LED Clear the text from
195. le random randint 8 12 time sleep random random q ChangeDutyCycle random randint 8 12 time sleep random random p ChangeDutyCycle random randint 3 5 time sleep random random q ChangeDutyCycle random randint 3 5 time sleep random random dimLaser 142 CHAPTER 9 THE CAT TOY def lightLaser GPIO output 11 1 def dimLaser GPIO output 11 O main loop while True check for input from sensor if GPIO input 19 moveServos time sleep 0 5 wait a half sec before polling sensor else dimLaser time sleep 0 5 Summary In this chapter you successfully constructed a two axis servo mechanism hacked a laser pointer to be fired by the Raspberry Pi and used your programming skills to randomly point and fire the laser to entertain your cat In the next chapter we re going to get your Pi out of the house and send it into the sky on a radio controlled airplane 143 CHAPTER 10 The Radio Controlled Airplane Many of us have long dreamed of flight of soaring through the air free as a bird Or as the pilot John Magee Jr put it slipping the surly bonds of Earth dancing through the skies on laughter silvered wings and topping the wind swept heights with easy grace Unfortunately slipping the surly bonds of Earth often takes time and money that we don t have and this may partly explain the advent of the radio controlled RC airplane While we m
196. le carrier into an SMS or text message You ll need an email account that s web accessible most of us have a gmail or yahoo account for instance You ll also need to know how to send a text via email with your mobile carrier Each carrier is slightly different but the basic concept is the same sending an email to a certain number lt mobile_number gt txt carrier net for example has that email delivered as a text I use AT amp T and if you send an email to 19075551212 txt att net it will be delivered as a text So using Python s smtplib library you can send an email to your phone It s probably easiest if I just show you with the following code def send text str HOST smtp gmail com SUBJECT Break in TO XXXXXXXXxXx txt att net FROM python example com text str BODY string join From Xs FROM To As TO Subject Xs SUBJECT text r n S smtplib SMTP smtp gmail com 587 s set debuglevel 1 s ehlo s starttls s login username gmail com mypassword s sendmail FROM TO BODY s quit 123 CHAPTER 8 THE HOME SECURITY SYSTEM Calling the send_text function with a string such as OMG I m being robbed will send you a text message Obviously this code is designed to work with AT amp T and uses a gmail account You ll need to modify it as necessary for your carrier and email provider gmail s smtp access is through port 587 as you can see in line 9 in the pr
197. le ttyAMAO 115200 kgdboc ttyAMAO 115200 so that the file reads dwc otg lpm enable 0 console tty1 root dev mmcblkop2 rootfstype ext4 elevator deadline rootwait Save the file and then edit the inittab file by typing sudo nano etc inittab Comment out the following line the very last line which tells the Pi to start a terminal connection by adding a hashtag to the beginning of the line T0 23 respawn sbin getty L ttyAMAO 115200 vt100 Now reboot by typing sudo shutdown r now When you re back up and running connect the GPS receiver to the Pi like so 1 Connect the receiver s VIN to the Pi s 5V pin 2 2 Connectthe GND to Pi pin 6 3 Connectthe Tx to Pi Rx pin 10 4 Connect the Rx to Pi Tx pin 8 When the receiver s LED starts to blink you know you have power Now you can test it by starting the gpsd program by typing sudo gpsd dev ttyAMAO F var run gpsd sock Then start the generic GPS client by typing cgps s The cgps client is a generic viewer it simply takes the data the gpsd program is receiving and displays it to the user It may take a moment for data to begin to stream but when it does you should see a screen like the one in Figure 10 2 147 CHAPTER 10 THE RADIO CONTROLLED AIRPLANE Figure 10 2 The cgps stream If you see nothing but zeros it means the GPS can t find a satellite fix You may have to wait a few minutes or even give the GPS a clear view of the sky My experi
198. leName we found earlier and removes the leading from the name so that we can save it If we didn t do this the fileName we would try to save under would be for example images flower1 jpg If we tried to save an image with that name Linux would attempt to save flower jpg to the images folder and then give us an error because the images folder doesn t exist By stripping the leading the fileName becomes images flower1 jpg and as long as there s an images folder in our current directory remember what I said about creating the directory first the file will save without incident Finally the last line of code does the actual downloading with the two parameters I already mentioned linkGet and filesave If you create an images directory in your current directory and then run this script answering jpg to the file type question the images directory should fill up with 12 different images of flowers Simple eh If instead you create a files directory and answer pdf you ll get 12 different boring PDFs in your files folder Creating Directories and Instantiating a List Now there are two more features we need to add to finish this bot First we aren t always going to know what directories we need to create ahead of time so we need to find a way to parse the folder name from the link text and create the directory on the fly Second we need to create a list of links that link to other pages so that we can then visit those
199. ll create another image jpg overwriting the previous image of the same name Also note that the parameter needs to be cast as a string with str in order to be inserted into the filename string given To keep things simple we re not going to use the camera s video capabilities in this program Rather we can take a picture with the nunchuk button wait until the camera process is finished and then continue with the program s main loop until the button is pressed again The Final Code Save the following code on your Pi preferably in its own folder It s also available as sub py on the Apress web site from subprocess import call import time import smbus import RPi GPIO as GPIO GPIO setwarnings False GPIO setmode GPIO BOARD def take stillpic num call raspistill o image str num jpg shell True def go forward GPIO output 19 1 IN1 on GPIO output 23 0 IN2 off GPIO output 11 1 IN3 on GPIO output 15 0 IN4 off 189 CHAPTER 12 THE SUBMERSIBLE def go backward GPIO output 19 0 IN1 off GPIO output 23 1 IN2 on GPIO output 11 O IN3 off GPIO output 15 1 IN4 on def go right GPIO output 19 1 IN1 on GPIO output 23 0 IN2 off GPIO output 11 O IN3 off GPIO output 15 1 IN4 on def go left GPIO output 19 0 IN1 off GPIO output 23 1 IN2 on GPIO output 11 1 IN3 on GPIO output 15 0 IN4 off set motor control pins left motor
200. ll scale AUV but for our purposes we re going to make a much simpler remotely operated vehicle We can use the Pi s onboard camera to take snapshots of our underwater explorations and we can control the sub with a hacked Wii nunchuk You won t be able to navigate via video because sending a video signal through a cable to an external monitor is slightly beyond the scope of this book but as long as you don t go too deep you should be able to follow the sub with a raft or small boat and direct it from the surface Again to keep the project within the scope of a single book chapter we re going to avoid depth control as well instead we re going to make the sub neutrally buoyant PRECAUTIONS IN THE EVENT YOU FRY YOUR PI This build involves both deep water and electronics two things that historically go together about as well as water and cats There is a very good chance of frying your Pi and or its associated bits if the enclosure you create is not completely watertight With that in mind you should do one or both of the following e Buy an extra Pi to use in your submersible It s relatively inexpensive and should you happen to fry it you ll still have your original Pi with all of its tweaks and added modules If you duplicate your SD card see the next bullet point the submersible Pi will be exactly like your regular one e Backup your SD card regularly just as do with your computer s hard drive If you back up as you go you won t
201. ly useful when you re four or five folders deep within a directory structure that may have repeated folder names like Users wdonat Desktop MyApplication bin samples Linux bin and the terminal prompt simply reads pi raspberrypi bin e rm Using the command rmis like dragging a file into the trash with one important difference for all intents and purposes you can t undo it so be sure you really want to delete that file e mkdir and rmdir The commands mkdir and rmdir create and delete directories The caveat with rmdir is that the directory must be empty or the operating system will not allow you to remove it You can however use the p option with rmdir which will remove a folder s also empty parent folders For instance typing rmdir p foo bar this directory 19 CHAPTER 2 LINUX BY THE SEAT OF YOUR PANTS will delete this directory bar and foo in that order e mv and cp The commands mv and cp while fairly straightforward can take some getting used to mv doesn t move a file so much as it renames it while destroying the old file in the process Typing mv myfile txt myfile2 txt will rename myfile txt to myfile2 txt In the mv command structure you can specify directory levels so in a sense you can mv a file from one folder to another For instance say you have a file named myfile txt in the MyFiles folder on your desktop You can move and rename it from within the folder by typing mv myfile txt My
202. m pump that removes melted solder from joints is a must have as is a helping hands tool See Figure 4 15 61 CHAPTER 4 ELECTRONICS AT 100 MPH Figure 4 15 Helping hands tool A helping hands tool comes in very handy when you need two hands to hold a connection and another two hands to solder that connection and you ve burned your wife s fingers one too many times and your kid s nowhere to be found You can even make your own out of stiff baling wire alligator clips and a wooden stand General Safety Rules Here is when I get to act like your mother and ask if you re being safe After all although we re building relatively innocuous projects in this book you re still dealing with some components that can seriously hurt you The tip of your soldering iron for instance averages around 450 F Hot glue even the low temp variety melts at about 250 F Sure programming is a fairly harmless activity but you ll also be cutting drilling sanding and doing any number of other tasks that have the capability to badly injure you So please take this safety talk seriously Working with Heat Keep in mind at all times that you are surrounded by tools and components that can get very hot and it would behoove you to remember which objects those are and treat them accordingly As mentioned earlier your soldering iron gets to around 450 F But also the solder you re using melts at around 350 F which means that the part you just solder
203. m sized radio controlled RC airplane Here are a few additional parts you ll need e Raspberry Pi with camera e GPSreceiver https www adafruit com products 746 e Antenna for receiver optional https www adafruit com products 851 e Medium sized RC airplane e RC battery and 5V regulator to power the Pi 145 CHAPTER 10 THE RADIO CONTROLLED AIRPLANE If you happen to already be an RC enthusiast you ll most likely have a plane you can use but if you re new to the sport you ll need to purchase a good starter plane As an amateur myself I can recommend a good beginner s plane the Switch by Flyzone shown in Figure 10 1 Figure 10 1 The Switch Image Flyzone Planes at http www flyzoneplanes com This plane is sturdy enough to endure a few crashes while you learn to fly it steady enough to be flown by an absolute beginner and most importantly powerful enough to carry the extra weight of a Pi GPS receiver and the battery to power them both Its name comes from the fact that as you become more adept at flying you can remove the wings from the steady top configuration and switch them to a lower mid configuration for more aerobatic maneuvers As you ll see the top configuration is perfect not just because it s easy for beginners but because the Pi and GPS can sit comfortably atop the wing Ready Let s start by creating a directory for our plane program mkdir plane and then navigate into it by
204. m that which you re using to power the Pi otherwise you ll get constant freezes and crashes With a breadboard that has two power channels you can run the 9V down one positive channel connect pin 2 on the Pi to the other positive channel and then wire the two negatives together Then you can connect the laser power and the IR sensor power to the Pi s power channel and connect the two servos to the 9V power channel and all your grounds will be tied together See Figure 9 10 which shows the various parts connected together using a breadboard IR Sensor Laser Pointer Figure 9 10 Final component interconnections 140 CHAPTER 9 THE CAT TOY Figure 9 10 is not completely accurate because the laser pointer is supposed to be attached to the servos but you get the general idea The pointer is powered with pin 11 the servos are powered with pins 13 and 15 and pin 19 is the sensor input Then everything is given its respective voltage to make it work There are a few mechanical engineering tasks involved in the building of this toy not the least of which is the best way to permanently attach the power and ground wires to the laser pointer While alligator clips are fine for testing as soon as the servos start jerking the pointer around in circles they re going to come undone The best solution to this is to solder the wires to the pointer parts If you can use sandpaper to roughen the point of the screw and the po
205. mall and fit in my robot parts box If size is an issue for you this particular hub might be a good fit for you As it happens I ve had no problems running everything I need to with it so feel free to copy my success with it Using a Wireless USB Dongle The last piece of hardware you re going to need is a wireless USB dongle When you re first setting up the Pi it s almost always a good idea to keep it hardwired to your Internet connection as long as possible This is because a hard connection is always faster than a WiFi one and you ll probably be downloading packages updates and libraries all sorts of good stuff In fact if you plan to use the same Pi for several different projects which is definitely an option even though they re so cheap you ll most likely plug it in again for each successive download you need It ll save a lot of time But eventually you ll want or need to go wireless after all part of the Pi s allure is its compact size and portability which is wasted if it s dragging an Ethernet cable behind it like a ball and chain So you ll need a wireless adapter And this my friends is where configuring your Pi can get very sticky WiFi support on ARM Linux can be patchy as the Foundation so eloquently puts it without some sort of direction you could spend months and hundreds of dollars trying out different dongles all to no avail Some adapters can make the Pi crash others won t connect to a network It may not s
206. mall parachute The group that launched the balloon tracks down the fallen package and retrieves the data In this way scientists and hobbyists can learn a great deal about the upper reaches of the atmosphere Although operating the radio controlled airplane with a Raspberry Pi in the previous chapter was cool it was also somewhat tame in that we logged its position and uploaded its path data to Google Earth The concept behind this project building a weather balloon is very simple but more advanced We ll inflate and launch a small weather balloon capable of sending the Raspberry Pi to at least 30 000 feet We ll then program the Pi to take a picture every so often giving us a pictorial record of our flight and use a small GPS unit to log our Pi s trip But we won t stop there because that s kind of boring and it s been done by many different hobbyists and professionals In addition we ll get an update in real time as to what the balloon is doing its latitude longitude and even altitude by programming the Pi to record itself speaking its coordinates every 15 seconds or so Then we ll broadcast that recording to a radio on the ground All we need to do is tune our small FM radio to a pre assigned frequency and we ll be able to hear our balloon talking to us giving us live updates on its condition Let s go shopping for parts Caution In the United States FAA regulations require you to notify the agency 6 to 24 hours before your launch
207. matter 4 eula windows Installit using all the default settings and start it up Set the FORMAT SIZE ADJUSTMENT option to ON in the tool s Options menu make sure you have the right SD card selected and click Format e For Mac users Download the Mac version ofthe formatting tool from https www sdcard org downloads formatter_4 eula_mac Install the tool with all the default settings by double clicking the downloaded pkg file Once it s installed open it and select the Overwrite Format option Make sure you have the right SD card selected and click Format Using NOOBS Now that the card is formatted correctly you can put the operating system on it Most users can use the Pi Foundation s NOOBS New Out Of Box Software from http www raspberrypi org downloads The NOOBS system upon first boot will actually present you with a choice of operating systems to install including two versions of XBMC Xbox Media Center Pidora and Raspbian For the purposes of this book and the subsequent chapters we re going to install Raspbian Once you ve downloaded NOOBS and be aware that it s a hefty 1 1 GB download unzip it using the extraction utility of your choice Windows right click Extract all Mac double click Then copy the extracted files onto your SD card That s it Your Pi is now ready to boot Connecting the Peripherals Ready to connect all those wonderful components Not so fast Kemo Sabe There
208. mba Service When you ve finished editing the configuration file restart your Samba service by typing sudo service samba restart When it s up and running again go to a Windows machine on your home network and open a command prompt At the prompt type net view NN192 168 XX XXX substituting the IP address of your Pi obviously You should get something back like you see in Figure 7 2 107 CHAPTER 7 THE MEDIA SERVER o IMicrosoft Windows Version 6 1 76011 Copyright lt c gt 2889 Microsoft Corporation All rights reserved Users rebecca gt net view 192 168 2 42 hared resources at 192 168 2 42 raspberrypi hare name Type Comment Media Drive The command completed successfully C Users rebecca gt Figure 7 2 Net view of a working Samba share Connecting to your Samba share as a shared network drive is unfortunately slightly different in every version of Windows Because this book is about the Pi not Windows I can t go into all of the specifics for each version using a graphical interface However if you don t mind using a command line interface the command to mount the Media folder on a Samba share located at 192 168 2 42 on the same domain is actually very simple It looks like this net use z 192 168 2 42 Media USER pi P Yes If everything on the Pi is set correctly you should see your Media folder mounted as a Z drive However Windows 7 is notorious for not wanti
209. me script as you did for the limit switch and test it by pressing down on the pad with your finger Voil You re now reading a value from a pressure switch This is perfect for reading a footstep from underneath a welcome mat for instance 121 CHAPTER 8 THE HOME SECURITY SYSTEM Connecting the Magnetic Sensor The magnetic sensor shown in Figure 8 9 is a little device that while not commonly used outside of certain specific applications can come in handy for applications like ours It measures the surrounding magnetic field and sends a signal when that field changes For that reason it is very good at determining when the relative position of two pieces of metal have changed for instance PHIDGETS Pmidgets com Figure 8 9 The magnetic sensor In order to make sure we don t get any false readings we can use some small external magnets to influence the sensor the one we re using comes with two small neodymium magnets for just that purpose To test our magnetic sensor we can again use our switch py code we ve been using Connect the jumper wires that came with the sensor to the connector block on the sensor and then connect them to your Pi red to pin 2 black to pin 6 and white to pin 11 Now just change the code to read import time import RPi GPIO as GPIO GPIO setwarnings False GPIO setmode GPIO BOARD GPIO setup 11 GPIO IN pull up down GPIO PUD DOWN prev input 0 while True input GPIO inp
210. minals but we re only going to use two because we re interested only in when the switch closes In our case we re going to use a limit switch not to determine when an object gets too close but to determine if a trip wire has been pulled You can mount the switch on a wall and run a thin thread or fishing line from the opposite wall to the switch s lever Position it so that if someone walks into the thread they ll pull the lever down activating the switch Because we re using a physical switch here rather than a sensor like the motion detector it s important that I introduce you to the concept of debouncing A common aspect of physical switches is that because they re often made of spring metals when they are first activated they tend to bounce apart one or more times before making a steady contact The result is a very fast on off on off on off chatter before the voltage settles at a steady HIGH or LOW To combat this we debounce the switch by reading from it only when it s no longer bouncing back and forth like so import time prev input 0 while True take a reading input GPIO input 11 if the last reading was low and this one high print if not prev_input and input print Button pressed update previous input prev_input input slight pause to debounce time sleep 0 05 120 CHAPTER 8 THE HOME SECURITY SYSTEM This little script illustrates the concept quite nicely It ignores a button press if it occurs less th
211. munication with the serial port Finally the loop function which is every Arduino sketch s main program loop prints the string Hello Raspberry Pi to the serial port every 1000 milliseconds one second Save the sketch and nameitpi test Now connect your Arduino to your Pi with the Arduino s USB cable Remember though it s a USB cable the Pi will actually be communicating via the serial protocol because the Arduino has an onboard USB to serial converter When the Arduino s green power light comes on you ll need to select it from the available boards in the Tools menu in your Arduino IDE See Figure 14 4 219 CHAPTER 14 THE RASPBERRY PI AND THE ARDUINO pi_test Arduino 1 0 1 File Edt Sketch EER Help 7 Auto Format CtrleT g Archive Sketch Fix Encoding amp Reload pi test gt Serial Monitor CtrH Shift M const int ledh O Arduino Uno void setup SerialPort b Arduino Duemilanove w ATmega328 Programmer p O Arduino Diecimila or Duemilanove w ATmegal6s pir Apc ghar A S Arduino Nano w ATmega328 Serial begitwwer J Arduino Nano w ATmegal168 Arduino Mega 2560 or Mega ADK void loop Arduino Mega ATmegal280 Arduino Leonardo Serial println Hello Pi Arduino Mini wi ATmega328 if Serial available O Arduino Mini w ATmegal68 Arduino Ethernet flash Serial read 0 O Arduino Fio delay 1000 c Crk BT wi ATmega328 A Arduino BT w
212. n a string is defined as an ordered collection of characters used to represent text based information Python doesn t have a char type like C and other languages a single character is simply a one character string Strings can contain anything viewable as text letters numbers punctuation program names and so on This means of course that gt gt gt X 4 and gt gt gt x 4 are not the same thing You can add 3 to the first example of x but if you tried it with the second example Python would give an error that x points to a string with a value of 4 not an integer because the 4 is enclosed in quotes Python does not distinguish between single and double quotes you can enclose a string in either and it will be recognized as a string This has a nice side effect you can enclose a quote character of the other type inside a string without having to escape with a backslash as you would have to in C For example gt gt gt Brian s gives you Brian s without any escape characters needed There are some basic string operations you will probably use many times in your Python career such as len the length of a string concatenation iteration indexing and slicing Python s equivalent of the substring operation To illustrate type the following bits of code into an IDLE session and see that the results match the output of what you see here gt gt gt len shrubbery 9 shrubbery is 9 characters long g
213. n emacs Command Keystroke s Open New Ctrl x Ctrl f Close Ctrl x Ctrl c Save Ctrl x Ctrl s Cut Ctrl w Copy Alt w Paste Ctrl y Jump to beginning of line Ctrl a Jump to end of line Ctrl e Start end select Ctrl space 27 www allitebooks com CHAPTER 2 LINUX BY THE SEAT OF YOUR PANTS So for instance if you want to move a line of text move your cursor to the beginning of the line Press Ctrl and the space bar the status text at the bottom left of the window will read Mark activated Then move your cursor to the end of the line with Ctrl and e The status text will disappear Now cut the selected text by pressing Ctrl w move your cursor to where you want to paste it and press Ctrl y It does take some getting used to so if you decide you like emacs there are many tutorials online that can take you through the process of learning the keystrokes Once you learn it it can be very powerful but always remember this If you get confused remember that most if not all of these commands are accessible from the menu Using nano As mentioned earlier nano is probably the easiest of the three editors to use and get used to To start a file in nano simply type nano testfile txt into your terminal and you should be greeted by a screen like the one in Figure 2 6 As with the other two editors if the specified file exists nano will open it if it doesn t exist nano will create it for you GNU nano 2 2
214. n how to use the Pi to protect your home network not from hackers but from physical intruders 110 CHAPTER 8 The Home Security System Living in modern times can be well let s face it It can be a scary stressful thing Bad guys and the crimes they commit are everywhere According to the FBI Crime Statistics web site there were approximately 9 million property crimes committed in the United States in 2012 the most recent year for which statistics are available The days of living on a peaceful street where neighbors knew each other and you could leave your door unlocked while you went to work are long gone Luckily we re able to protect our homes and also to watch those homes with cameras both still and video that are mounted where we need them and capable of live streaming that video to any of our always connected devices such as our laptops or phones We can outfit our house with sensors such as motion sensors and trip switches and use the information gathered from those sensors as a trigger to perform certain actions If you re willing to spend the money you can install systems that do everything from protecting your home from fire and burglars to alerting you to carbon monoxide CO leaks As it happens the Raspberry Pi is perfect for doing all those things for quite a bit cheaper than an entire network of closed circuit cameras and the computer system to run them Not a lot of computing power is necessary it
215. n members of that class Perhaps the easiest way to illustrate this is with an example using shapes In this example a shape is a class of objects That class has associated values such as name and numberOfSides That class also has associated methods like findArea or findPerimeter The shape class has subclasses which are more specific A square is a shape object with the value shapeType equal to square and numberOfSides equal to 4 Its findArea method takes the numberOfSides value and squares it Meanwhile a triangle object has different values for name shapeType and numberOfSides and its findArea method is different This example while a quick introduction to objects also illustrates the concept of inheritance an integral part of OOP The triangle object inherits its name numberOfSides and findArea parts from its parent class shape though those parts have different values and implementations If an object inherits from the shape class it will also inherit those parts It may not necessarily use those parts but it has them It may have additional parts the circle object may have a radius value for instance but it will always have those parts If you start to use classes in your programming Python is simpler to understand than its counterparts like C or Java You can pretty much name any object or method with the following syntax object attribute whether that attribute is an object or a method If you have a circle object name
216. n on both sides of the connector until they snap into place See Figure 12 2 i wppenttti ttt ELEI a kah U et ity A layin JE d van Figure 12 2 Connecting the Pi s camera cable You should have enabled the camera support when you set up your Pi in Chapter 3 if you didn t however it s not difficult From the terminal type sudo apt get update and sudo apt get upgrade to make sure your Pi is running all the latest kernel fixes and software updates When both of those finish type sudo raspi config to start the configuration program Navigate to the camera selection and click Enable Then select Finish and reboot the Pi 177 CHAPTER 12 THE SUBMERSIBLE When the Pi comes back up you can use its built in camera functions raspistill and raspivid to experiment with the camera For a full list of commands simply enter raspivid Or raspistill at the command prompt for instructions For example to take a still picture in a cartoon format simply type raspistill o image jpg ifx cartoon and the image will be saved in whichever directory you happen to be in You can change the image resolution height width effects and delay and even set up a time lapse situation using the t1 flag which we may use later Controlling the Sub To control the sub we are going to use two DC motors a motor driver chip already placed on a printed circuit board and a Wii nunchuk as shown in Figure 12 3 Using
217. nd initiate I2C communication by writing to the nunchuk bus write byte data 0x52 0x40 0x00 time sleep 0 1 while True try bus write byte 0x52 0x00 time sleep 0 1 data0 bus read byte 0x52 data1 bus read byte 0x52 data2 bus read byte 0x52 data3 bus read byte 0x52 data4 bus read byte 0x52 data5 bus read byte 0x52 joy x datao joy y data1 accel x data2 lt lt 2 datas amp Ox0c gt gt 2 accel y data3 lt lt 2 datas amp 0x30 gt gt 4 accel z data4 lt lt 2 datas5 amp OxcO gt gt 6 buttons data5 amp 0x03 button c buttons 1 button_c is True if buttons button z buttons 2 button_z is True if buttons 2 print Jx s Jy s Ax s Ay Xs Az s Bc s Bz s joy x joy y accel x accel y accel z button c button z except IOError as e print e If you haven t already create a folder for your submersible program save this script in that folder and run it After importing the necessary modules the script creates a bus over which all communications will be made with the nunchuk It then begins communication by writing to the nunchuk s I2C address bus write byte data It then enters a loop where it continuously reads the 5 byte strings coming from the nunchuk data0 datal and so on and categorizes them as joystick directions accelerometer readings and button presses in that order Then it prints those values to the screen and
218. nd speed and the easiest way to do that is with a friend and a car With your anemometer held out the window and your Pi connected to your laptop via an ad hoc network see the sidebar have your friend drive for a few minutes at 5 MPH while you run the encoder script repeat the process at 10 15 and 20 MPH until you have enough data to correlate wind speed with RPS When I drove around with my anemometer hanging out the window I got the RPS readings shown in Table 6 1 Table 6 1 MPH correlated to RPS reading using an anemometer MPH RPS 5 5 8 10 9 23 15 10 8 20 11 7 The correlation of MPH to RPS is obviously a logarithmic relationship which means we can use a little algebra eek to calculate wind speed based on revolutions per second If you plot these values on a graph you get Figure 6 8 88 CHAPTER 6 THE WEATHER STATION RPS vs MPH y 4 3021In x 0 9594 RPS Figure 6 8 RPS vs MPH As you can see from the equation the relationship between revolutions per second and wind speed is a logarithmic not a linear one So we ll have to use the inverse logarithmic function or e to solve for wind speed in terms of revolutions per second I don t want to bore you with the math so just take my word for it that wind speed e 0 099 43 We ll be able to substitute that calculation into our final program as you ll soon see HOOKING YOUR PI TO YOUR LAPTOP VIA AN AD HOC NETWORK If you re like me most of
219. ng this page we can start with something simple like images So let s modify our webbot py code and make it look like this import mechanize import time from bs4 import BeautifulSoup import string import urllib start http www irrelevantcheetah com browserimages html filetype raw input What file type are you looking for n br mechanize Browser Y br open start html r read soup BeautifulSoup html for link in soup find all a linkText str link fileName str link get href if filetype in fileName image urllib URLopener linkGet http www irrelevantcheetah com fileName filesave string lstrip fileName image retrieve linkGet filesave 76 CHAPTER 5 THE WEB BOT This last section of code starting with the for loop requires some explanation methinks The for loop iterates through all of the links that Beautiful Soup found for us Then linkText converts those links to strings so that we can manipulate them We then convert the body of the link the actual file or page to which the link points to a string as well and check to see if it contains the file type we re looking for If it does we append it to the site s base URL giving us linkGet The last two lines have to happen because of the retrieve function As you recall that function takes two parameters the URL of the file we re downloading and the local name we d like to save that file to filesave takes the fi
220. ng to play nicely with Samba shared folders If you re confident you have everything configured correctly but still can t see the contents of the folder you re getting an Access Denied error for example try it with a different OS Your Windows OS may be the problem Connecting with Linux OS X But wait I can hear some of you screaming weakly from the back of the room What if we want to connect to our server with a Linux or Mac box Well first of all if you are running a Linux box somewhere else in your house you probably don t need any help connecting to a Samba share If however you re using a Mac it s again pretty easy to connect From your Finder click Go and then Connect to Server See Figure 7 3 108 CHAPTER 7 THE MEDIA SERVER Finder File Edit View Window Help Ej All My Files 7 Documents E Desktop Downloads A Home E3 Computer 4 AirDrop Network Applications Utilities Recent Folders Go to Folder Connect to Server Figure 7 3 Connection menu In the window that comes up enter the address and shared folder and click Connect See Figure 7 4 Enter the name and password you use to log in to the Pi in the next window and the folder should mount as a shared drive accessible from any Finder window If you happen to be using Mac s Mavericks OS 10 9 you may also have trouble connecting as pi but you may be able to connect as Guest This is
221. nmen ena 209 ENDS ISBIPCAL Sm vo A nA 210 Experimenting with Motor Controllers eese tete tnter tnnt trennen tnn 212 Using the Open Collector Drivers eeesesiseeeseeeeeeeenennen ene tntn tnnt tna tntntn natn tntn enata tn tn inanes 213 Using the Digital Analogue Converters esessssesseeseeeeeeeen eene tnter natn tnnt tntn enata tn tn enata 213 jl gnrig em 214 Chapter 14 The Raspberry Pi and the Arduino eeen 215 Exploring the AFOUITID escent 215 Installing the Arduino IDE on the Pj copre ricette t te eerte mete at etm 218 ITE ra ok ces ok cc ie secs P 223 The Arduino and the Gertboard eeeeeeneeenennnenennnenennnennnnnnennnnnn nennen 224 Sumindtyc sot mE E Lt te 225 Li deem m PD E EDD ETE 227 xiv About the Author Wolfram Donat is tallish with hair and four limbs attached in approximately the correct locations He is a Computer Engineer author and programmer with interests in robotics animatronics automation and embedded systems He wrote his first BASIC program on a Commodore VIC 20 more years ago than he cares to admit He currently lives in Anchorage Alaska with his wife son and menagerie of animals XV About the Technical Reviewer Chaim Krause presently lives in Leavenworth Kansa
222. nne nnn nnnnnnn 16 Linux Files and the File System eesssessessesseseeesesene ene nntn tnnt tnn tn natn tn tn tna tnmen tna tate tn enata 17 AETAT o EEEE EEE TE 17 Commands nrnna a tte eee 18 Exercise Navigating in the Linux File System sees 21 Sells MV ENUN iaaa cvsesucyesansuce aanere sian utessaecuensiaeseunssinsuins ansuibibansethenaestabinaastaeikerants 22 Package Managels scsscscsccscsecsecsecsecsecsecsessecsecesessessesaesaesaesaesaesaesassaesassaesassaesaesaseassaseaseaees 23 JE qd eit ED sears ee POP ae a an REY OLET AER REAR EE Ee AR EIE 24 ILU ENCEINTE 25 Sumitdly osse oda uM uL aaa d a d DR ME 29 Chapter 3 Introducing Python 1 1eenereeeeenrne enne nnn nnn nnn nnn 31 Scripting vs a Programming Language eesseeeeeeee ener enne nnne nnn nnn nnn nnn nnn nnns 31 The Python Philosophy a Eoo Loro 33 Getting Started with Python sese eere eene nennen nnn nnn nnn nnn nnn tn anna 34 Running Python Using IDEE 5 5 23 13 33 0 nitet e cedenieite iicet nra tabeniied e ine aci udi lac eade 34 Running Python Using the Terminal 5 t etra rne neueren reta denen daten 37 Running Python Using Scripts eesessssssseseseseeeee nennen enata tnn tnn tn tntn na
223. nnect upon mission launch Figure 11 3 Camera positioned in the cooler 168 CHAPTER 11 THE WEATHER BALLOON Poke a small hole in the bottom ofthe cooler This is where the GPS antenna FM antenna and balloon tether will go Slip them through the hole and connect the FM antenna to the Pi s pin 7 Attach your GPS board to the Pi if it isn t already see the section Setting Up the GPS Receiver earlier in the chapter and connect the antenna to the GPS The two antennas should be hanging freely out of the bottom and the tether should be connected to your fishing line spool Fasten the free end ofthe tether to your cooler in a way that won t tear the cooler I cut a length of PVC pipe the length of the cooler and tied the tether to it See Figure 11 4 Figure 11 4 Interior of the cooler showing the tether attached to a PVC pipe Now break open the hand warmers and activate them by shaking and mixing the contents Lay them on the bottom of the cooler and put your Pi and battery pack on top of them The hand warmers are important because it gets pretty cold in the upper atmosphere cold enough to cause your electronics to stop working The warmers should keep the interior of the cooler warm enough to allow your Pi to continue working at the apex of its flight You ll need to attach the parachute to the lid of your cooler as a way to save your Pi in case the balloon bursts Ifound that the best way to do this is to poke a hole in the l
224. nnnnnnnnnnnnn 111 Chapter 9 The Cat TO assuassonisexiciuisas amu RE MuE rc DII cR I UUFE ENSE V Dra EE n EIS rd K aS EV rA S 127 Chapter 10 The Radio Controlled Airplane eee 145 Chapter 11 The Weather Balloon 11 eereere eere rre nnn nn nnnm nnn nnn 161 Chapter 12 The Submersible 21111 reeere rere eere ena nnn uana unu 173 Chapter 13 The Gertboard ioiscconon cuida e ixdui a acKR OK xa vini ae ior s Gio GR an iin nnna 201 Chapter 14 The Raspberry Pi and the Arduino eeenn 215 ipi e P 227 v www allitebooks com Introduction In 2006 when Eben Upton and the other founders of the Raspberry Pi Foundation looked at the state of Computer Science CS programs in universities they were dismayed Computer science programs were being reduced to CS 101 How To Operate Microsoft Word and CS 203 Optimize Your Facebook Page Nobody they realized was learning how to program any more least of all before they entered college So they hatched a plan create a small cheap computer that kids could learn to program on like the Amigas Spectrums and Commodore 64s of yesteryear They put an ARM processor on a board gave it eventually 512 MB of RAM and a VideoCore GPU and allowed users to interface with it using a USB keyboard mouse and
225. nput if total 90 rps 1 time time current speed math exp rps 0 95 4 3 totalSpeed totalSpeed speed total 0 current time time speed totalSpeed 10 average speed out of ten turns return speed def checkWindDirection write byte 0 0b01110000 write byte 0 0b00100000 write byte 0 0b00000000 scale 0 92 x offset 106 use the offsets you computed yoffset 175 use the offsets you computed x out read word 2c 3 x offset scale y out read word 2c 7 y offset scale direction math atan2 y out x out if direction 0 direction 2 math pi direction math degrees direction return direction main program loop while True temp checkTemp humidity checkHumidity pressure checkBarometer speed checkWindSpeed direction checkWindDirection os system clear print Current Conditions print print Temperature str temp print Humidity str humidity print Pressure print Wind Speed print Wind Direction Str pressure str speed str direction time sleep 30 99 CHAPTER 6 THE WEATHER STATION Summary In this chapter you built a weather station from scratch and installed the necessary sensors to keep tabs on the weather goings on including barometric pressure temperature humidity wind speed and even wind direction You ve learned more about the I2C interface and should
226. ns 135 Connecting the Laser to the Servo eren eere nnne nnne nnns 136 Connecting the Motion Sersor Aden cc acc ce ch 137 Connecting All the Bits oso e e Qoi s e ei OE De E E Re DOES C E GER a DER Ce usa 140 LIES STR PETS S PAR TE CI OI OI ON UN SPUR HB NESSUN NIS SUN 142 Sumario cec th MexcAS a AA LLLA DDR LEAL IA DIRAIS 143 Chapter 10 The Radio Controlled Airplane uere 145 A Shopping List of PALEIS eco qene inset eese erac avc ras eo erae tuo ras be crat atr dean ae veras deerat ever etae rat n 145 Connecting the GPS Receiver to the Pi eeeseeeseeeeeeeere eren nnne nnns 146 Setting Up a Log ENG E 148 Formatting a KML FI cocco inne nnn nan RAR AeA KAA MAAR c aes 149 Using Threading and ODJeclss seo teo Sto SS SUE du elena c addons 151 Setting Up Automatic Startup eere esses eere nennen tnnt tnn tn strana 152 uninBidle C 153 MNE IMAL OOo d d t ad d ode eee E Cn ME 157 The Plarie Program rante tcn re rior nf dd a a C RR ahai 158 KME Conversion Program ii a e Ee ate Nae RO e c E aaaea 159 Sunabie c cM Lt M M D M MM M T 159 Chapter 11 The Weather Balloon 11eeeeeen nnne nnnm 161 A Shopping List of PANS T 161 Setting Up the GPS REGCIVER iisisti aiiai aiiai 162 A E t DE e ETT 164 xii CONTENTS I3 mago
227. nsions Constructing the Servo Mechanism Our cat toy is going to be sweeping a laser pointer in two directions which means we need a servo capable of the same thing While servos aren t generally capable of 2 dimensional motion we can easily construct a pan and tilt servo mechanism using two normal servos attached to each other Note This procedure will permanently bond your two servos making them inseparable so make sure you have others to use for other projects However remember that a pan and tilt setup like you re making here is a handy thing to have for projects where you need to move an item in two dimensions and you ll probably use it again So it s not like you re trashing the two servos completely All you need to do is mount the body of one servo to the horns ofthe other To make a secure connection you may need to remove the screw holding the servo horns of the base servo let s call it the X axis servo to keep the task simple and file down the plastic a bit You re trying to flatten out the top ofthe servo as much as possible to mate it tightly with the body of the other Y axis servo When it s as flat as it s going to get use a strong epoxy or adhesive to glue the Y axis servo body to the horns ofthe X axis servo I used Gorilla Glue and got the result in Figure 9 4 134 CHAPTER 9 THE CAT TOY Figure 9 4 Bonded X and Y servos The laser pointer can now after some not so minor modifications be mounted to
228. num 1 increment picture number time sleep 3 except KeyboardInterrupt SystemExit gpsp running False gpsp join 158 CHAPTER 10 THE RADIO CONTROLLED AIRPLANE KML Conversion Program This program is run when the Pi is back on the ground It takes the GPS logging file and converts it to a KML file It s available as km1 py from Apress com import string open files for reading and writing gps kml kml kml kml kml kml kml kml kml kml kml kml kml kml kml kml for kml kml kml kml kml open locations log r open plane kml w write xml version 1 0 encoding UTF 8 gt n write kml xmlns http www opengis net kml 2 2 gt n write lt Document gt n write name Plane Path lt name gt n write description Path taken by plane description An write Style id yellowLineGreenPoly gt n write lt LineStyle lt color gt 7fooffff lt color gt lt width gt 4 lt width gt lt LineStyle gt n write lt PolyStyle gt lt color gt 7f00ff00 lt color gt lt PolyStyle gt n write lt Style gt n write Placemark name Plane Path lt name gt n write styleUrl ityellowLineGreenPoly styleUrl Wn write lt LineString gt n write lt extrude gt 1 lt extrude gt lt tesselate gt 1 lt tesselate gt n write lt altitudeMode gt relative lt altitudeMode gt n write lt coordinates gt n line in
229. oard manual has a selection of scripts to experiment with written in both C and Python So we ll do that now You ll notice that many ofthe scripts are almost duplicates with names like leds rg py and leds wp py The reason is that there are two different libraries you can use to access the Pi s GPIO pins RPi GPIO which you re familiar with from this book and WiringPi a library written and released by Gordon Henderson While the WiringPi library is effective and even addresses some issues with the Pi that RPi GPIO does not such as an easy way of controlling outputs with PWM I chose to use RPi GPIO for the projects in this book so we ll concentrate on that version of the scripts here If you re interested however I recommend you check out the WiringPi library because it s intended to make the interface to the Pi resemble the Arduino s Wiring library Configuring the Preliminary Jumper Setup Before we use the board for a few simple projects we need to install some jumpers The first one of course was illustrated in Figure 13 9 it sends power to the rest of the board from its 3 3V input The second batch of jumpers need to be installed on the output side of every IC in the buffered I O section There are three chips shown in Figure 13 5 each with eight output pins directly above it Using four jumpers per chip connect each pair of pins together See Figure 13 10 209 CHAPTER 13 THE GERTBOARD Figure 13 10 Jumpers in
230. od by most computers Browsers are programmed to interpret the language of the pages and display those pages in a certain way For instance the tag pair html and lt html gt indicate that the page is in HTML i and lt i gt indicate that the enclosed text is italic while a and lt a gt indicate a hyperlink which is normally displayed as blue and underlined JavaScript is surrounded by script type text javascript script tags and various other more involved tags surround various languages and scripts All of these tags and formats make browsing and reading raw web pages easy for humans However they have the effect of also making it easy for computers to parse those pages After all if your browser couldn t decode the pages the Internet wouldn t exist in its current form But you don t need a browser to request and read web pages only to display them once you ve got them You can write a script to request web pages read them and do pre scripted tasks with the pages information all without the interference of a human Thus you can automate the long boring process of searching for particular links pages and formatted documents and pass it to your Pi Therein lies the web bot 69 CHAPTER 5 THE WEB BOT A Request Example For simplicity s sake let s begin by saying we have requested the page http www carboni11 com links html The page s text is pretty simple it s a static page after all with no fancy
231. oduction to object oriented programming OOP Think of a class as a set of similar objects that share certain characteristics For instance squares triangles and pentagons are all members of the shape class they have sides a calculable perimeter and a calculable area An object is one particular member or instance of that class myRectangle for example is a certain instance of the shape class When you define a class you define its characteristics such as the fact that a shape has sides and is a closed object You can also define functions that are unique to that class To illustrate every member of the shape class can have a function defined that specifies how to calculate its perimeter That calculation may vary according to the individual shape object so it is unique to that object but every shape object has a defineArea function The thread we create in our final program will contain one object a member of the Thread class with a set of variables and functions unique to it So when we start our thread it will have an associated GPS polling function that will handle the location retrieval and picture taking 151 CHAPTER 10 THE RADIO CONTROLLED AIRPLANE Our thread object will be defined like so class myObject threading Thread def init self function used to initiate the class and thread threading Thread init self necessary to start the thread def run self function performed while thread is running
232. oil disaster in 2010 A fleet of submersibles was used to cap the oil well and stop the spill in 5 000 foot depths far below what human divers could reach They are routinely used to conduct maintenance on deep sea oil rigs and offshore wave farms There are basically two kinds of submersible ROVs and AUVs ROV stands for Remote Operated Vehicle and describes a sub that is remotely controlled from a ship via a tether a cable that provides both power to the sub and two way communication with its onboard systems Ordinarily an onboard camera sends a video signal up the tether to a monitor in the control room where a specially trained operator uses the video feed to control the sub with a high tech version of an Xbox controller The remote operator controls the sub s propulsion steering and depth and that person is also able to work the vehicle s grippers and sample collectors assuming it is so equipped AUV on the other hand stands for Autonomous Underwater Vehicle and describes a submersible that works without human intervention or control It may or may not use an onboard camera if it does the video from the camera is often used only for data gathering purposes not for navigation An AUV has an array of onboard sensors and a relatively sophisticated onboard computer that is programmed to perform a variety of tasks and movements based on information from the sensors Using the Raspberry Pi you can actually construct either an ROV or a fu
233. ollowing equation V D 256 x 2 048V The analogue to digital converter on the board is also from Microchip and is a 10 bit MPC3002 It returns a digital HIGH of 1111111111 when an analogue voltage of 3 3V is applied If you apply a lower voltage the 10 bit value will be adjusted accordingly So if you re trying to read that pressure sensor I mentioned and it s only reading 2 7V the returned value from the MPC3002 will be lower and your program can act on that lower value however you wish Summary That is a concise and useful overview of the Gertboard and its various components You got a tour of the board learned how to use jumpers to connect various components and used some available Python programs to test some of the different uses for the board The one section we didn t cover in detail or experiment with is the Atmega chip and there s a reason for this Icover that in much more detail in the next chapter on the Raspberry Pi and the Arduino 214 CHAPTER 14 The Raspberry Pi and the Arduino Peanut butter and jelly Batman and Robin Dr Jekyll and Mr Hyde Some things are just meant to go together and we know it from the moment we first lay eyes on the combination Such is the case with the Raspberry Pi and the Arduino Many hobbyists and engineers including me had been using the Arduino for projects but were wishing there was a device similar in size with just a bit more power Well our wishes were grante
234. om subprocess import call call raspistill o image jpg shell True The video command is almost the same from subprocess import call call raspivid o video mp4 shell True We can set each command within its own function and call that function when the appropriate button is pressed on the nunchuk Similarly we can set up functions to run the motors and call those functions according to the position of the joystick All of this happens within a while loop and continues until we kill the program or the batteries die Starting the Program Remotely There are several ways to get the Python program running once you power up your submersible as you won t have a keyboard mouse or monitor connected to the Pi It would seem that the easiest way would be to set up a static IP address remotely log in to the Pi from a laptop and then start the program from there However this will only work if you are logged on to a wireless network and chances are that there won t be any networks available out on the middle ofalake or ocean or wherever you happen to be using your submersible You could set up an ad hoc network which is where the Pi and your laptop create a small exclusive network and then log in to the Pi from your laptop However setting up an ad hoc network can be problematic and if it doesn t work for some reason you ll be unable to access your Pi rendering your submersible useless 187 CHAPTER 12 THE SUBMERSIBLE Aft
235. ompleted form is listed at the end of this chapter It s also available for download as webbot py from the apress com web site 74 CHAPTER 5 THE WEB BOT To start the process of writing your bot use your text editor either Leafpad or nano and begin a new file called webbot py Enter the following from bs4 import BeautifulSoup import mechanize import time import urllib import string start http raw input Where would you like to start searching n br mechanize Browser Y br open start html r read Later we may need to fake a user agent depending on the sites we visit but this code will work for now Reading a String and Extracting All the Links Once you ve got a browser object which is called br in the preceding code you can do all sorts of tasks with it We opened the start page requested from the user with br open and read it into one long string html Now we can use Beautiful Soup to read that string and extract all of the links from it by adding the following lines soup BeautifulSoup html for link in soup find all a print link get href Now you can run the script to try it out Save it and close it Open a terminal session and navigate to the same directory in which you created webbot py Then type python webbot py to start the program and type example com when it asks where to start It should return the following and then quit http www iana org domains exampl
236. omputer programming language s print statement e grep Though man is probably the most important of these commands grep is probably the most powerful It is a search program that can search files and directories using whatever input you give it in the form of regular expressions and pipe that output to the screen or to another file Its use of regular expressions is what makes it so powerful if you re not familiar with them a regular expression is a sequence of characters that form a search pattern and often that sequence of characters seems like a foreign language As a quick example grep a ple fruitlist txt will search fruitlist txt for all lines that begin with an a followed a single character followed by ple and print those results to the screen Using the or pipe allows you to send those results to different output such as a text file grep s power and complexity is such that you could write chapters about it for now just be aware that it exists 20 CHAPTER 2 LINUX BY THE SEAT OF YOUR PANTS e filename This command to run an executable file is pretty simple Note that this works only on files that are executable by your user name it ll give you an error if the file doesn t have the correct permissions or simply isn t an executable file e exit The final important command is simply exit this stops whatever job is running in the terminal also called a shell and closes the terminal itself E
237. on It has two pins MOTA and MOTB which are connected to the two wires coming from a standard DC motor The two pins can handle a maximum of 18V DC and 2A Each of them can be set high or low including with a pulsed width modulation PWM signal to control the motor speed and the result of different combinations of HIGHs and LOWs are shown in Table 13 1 Table 13 1 Motor Speeds and Directions MOTA MOTB Motor Direction LOW LOW STOP LOW HIGH CLOCKWISE HIGH LOW COUNTERCLOCKWISE HIGH HIGH STOP 212 CHAPTER 13 THE GERTBOARD So for example if you needed your motor to turn clockwise you d send a 0 to MOTA and a 1 to MOTB Again the Python code that comes with the examples is an excellent way of seeing what the motor driver can do Open motor rg py and take a look at it Again you should recognize the first few imports and then a few variables are declared as are some functions designed to run the motor Some wiring instructions are printed depending on your board model and then the main program starts To run it connect one wire of your motor to MOTA and another to MOTB and then the and leads of your power to the MOT and MOT pins Then run two jumper wires from GP17 to MOTB and GP18 to MOTA and type sudo python motor rg py at the prompt The motor will go through its paces going from zero to full speed and back to zero in one direction and then repeating the process in the other direction As you can tell f
238. on it outputs a HIGH signal on the output pin which then travels to the Pi s INPUT pin With the GPIO pin configured as an INPUT we can read that signal and execute the Python script controlling the toy only when that signal is present Before we continue I need to discuss the important concept of a pullup or pulldown resistor Whenever you have an input in electronics if that input is not directly reading anything it is referred to as a floating input That means the value read from that input could be absolutely anything We need to define that input s empty state so that we ll know when that input changes To define an input s empty state we normally connect a resistor 10K or 100K are common values between the input and either a positive pin thus creating a pullup resistor or a ground thus creating a pulldown resistor Which one you use is not important it s just important that the input is pulled up or down Thus if nothing is being read on the pin and it s connected to a ground via a pulldown resistor it will read 0 When it no longer reads 0 we ll know that it s receiving input In the case of our IR sensor we need to define the value read at the pin when no motion is detected as LOW so we ll use a pulldown resistor Luckily to keep this process simple the GPIO library allows us to do that in code when we define a pin as an input like this GPIO setup 11 GPIO IN pull up downzGPIO PUD UP If w
239. oot dev mmcblkop2 rootfstype ext4 elevator deadline rootwait The boot cmdline txt file passes arguments to the Linux kernel as the Pi boots After you save it edit the inittab file by typing sudo nano etc inittab and comment out the line that tells the Pi to start a terminal connection the very last line T0 23 respawn sbin getty L ttyAMAO 115200 vt100 162 CHAPTER 11 THE WEATHER BALLOON Now reboot by typing sudo reboot While the Pi reboots solder the headers that came with it onto your GPS board You won t need to use all the connections for this project you ll only need four of them in fact but you may need the other pins later so make sure you connect those as well When the Pi comes back online connect your GPS receiver to it Using jumpers follow these steps 1 Connect the board s VIN to the Pi s 5V pin 2 2 Connect the GND pin to the Pi s ground 6 3 Connect the Tx and Rx pins to the Pi s Rx and Tx pins respectively 10 and 12 You should immediately get a blinking red light on the GPS unit letting you know the board is powered If you purchased the optional external antenna for your GPS never a bad idea connect it to the small connector on the board It may take a while for your unit to see any satellites particularly if you re indoors However you ll know when it does the red light that was previously blinking once per second will slow down blinking once every 15 seconds indicating
240. otor and the outer terminals allow you to attach a power source capable of delivering more current than the Gertboard or the Pi can safely deliver The direction and speed of the motor is controlled by two headers located just above the GPIO pins labeled appropriately MOTA and MOTB Open Collector Driver On the right side of the board is a ULN2803 chip that is used as an open collector driver The six ports are used to turn on and off external devices that require different voltage higher current or separate power from that used on the Pi or Gertboard See Figure 13 7 In a nutshell the open collector connects the ground of an external circuit to the ground on the board and it gives the circuit power Each port can take up to 50V and put out 500mA 207 CHAPTER 13 THE GERTBOARD oe OR Oe oR es XGGE gt Ouixxm ER aha bakataake SETINMIUIEM ory eg8688888 M d TERTS ZZIIEIELITIEFIIITUIT E IILII Figure 13 7 The open collector As mentioned earlier your board may look slightly different from these pictures because there have been considerable modifications and improvements to the design since the board was first released but the general design is the same As you can probably now see the Gertboard greatly increases the Pi s capabilities when it comes to interfacing with the physical world With the Gertboard s onboard motor controller and its collector drivers that allow it to turn external circuits on and o
241. our audio from 44100 kHz to 22050 kHz Start installing it by typing sudo apt get install ffmpeg 165 CHAPTER 11 THE WEATHER BALLOON into your terminal There are many different installation and configuration options but this is the easiest and most straightforward Now to convert our position wav file we use the following syntax so type ffmpeg i position wav y ar 22050 position wav Depending on when you re reading this chapter you may get the following deprecation warning This program is only provided for compatibility and will be removed in a future release The command should still work but if you prefer you can use the replacement s command avconv like so avconv i position wav y ar 22050 position wav That s it position wav has now been re encoded with a 22050 kHz sample rate and is ready to be broadcast If we want to broadcast the contents of position wav we would type in a terminal sudo pifm position wav 103 5 22050 103 5 FM is the frequency it will be broadcast to Adjust for your local stations of course Preparing the Pi If you re reading this chapter after the RC plane chapter you may recognize much of the setup here as many of the parts of this project are very similar The first thing you need to do is to make sure that the gpsd module will be running every time you start the Pi To do that open your rc local file by typing sudo nano etc rc local and add the following line to th
242. ource Enter the Gertboard An add on circuit board it s about the size of an index card and significantly extends the functionality of your Raspberry Pi While you most definitely don t need one to work with your Pi having one makes it much easier to do things you couldn t do otherwise For example you can add more sensors drive external motors and much much more It owes its existence and its name to its designer Gert Van Loo Gert was one of the original volunteer engineers who donated great portions of his time to the Raspberry Pi project and helped with the design that eventually became the Raspberry Pi model B Because he wanted to further expand the capabilities of the Pi he designed the Gertboard which was first available only as a kit you had to solder the board together before you could use it However you can now buy a fully assembled board from several online retailers Development continues on the Gertboard so there s a good chance that your board may differ from the one in the pictures in this chapter but the overall placement of parts and sections hasn t changed ICs integrated circuits may differ but the headers used to plug into them won t There is even another version of the Gertboard called the Multiface board put out by Tandy The Multiface version is designed with all through hole parts which means that it can be sold as a kit and requires no surface mount soldering In this chapter I ll give you a quick
243. ource enough power through its onboard USB ports to power certain adapters but it often has problems using a USB adapter that is connected via a hub For this reason if no other it s always a good idea to plug the wireless adapter into one ofthe Pi s onboard ports and plug your hub into the other Then your mouse and keyboard are connected via the hub rather than the dongle Fortunately the Pi community has collectively spent those hundreds of dollars and months testing out all of those adapters and it has published the results on the forums It turns out that the Pi plays well with adapters using the Ralink RTL8188CUS chipset CHAPTER 1 INTRODUCING THE RASPBERRY PI Unfortunately you may have noticed that determining what chipset a certain adapter uses is no easy task even if you re in the store physically inspecting its packaging spoken from experience For whatever reason wireless USB adapter chipsets are not commonly advertised But again the Pi community has experimented and determined that the following two adapters work very well with the Pi e Edimax EW 7811Un e Ralink RT5370 Both are available on Amazon com for very reasonable prices less than 10 US As you can see in Figure 1 5 the Edimax adapter is small it s so small in fact that it s actually quite easy to lose Not that I would lose track of a wireless adapter But you might Figure 1 5 An Edimax adapter If you ve purchased your adapter and have a
244. p rather quickly if you re downloading free documentary movie files So you ll need an external USB hard drive either a full blown hard drive or a smaller flash drive Again this is where some experimentation may come in handy because some external drives won t work well with the Raspberry Pi Because they re not particularly expensive these days I would buy one or two medium sized ones and give them a try I m currently using an 8 GB flash drive by DANE ELEC shown in Figure 5 2 without any problems Figure 5 2 Common flash drive to store files A note on accessing your jump drive via the command line a connected drive such as a flash drive is accessible in the media directory that is cd media will get you to the directory where you should see your drive listed You can then navigate into it and access its contents You ll want to set up your Python script to save files to that directory media PENDRIVE for example or media EnglebertHumperdinckLoveSongs Probably the easiest way to do it is to save your webbot py script in a directory on your external drive and then run it from there Writing the Python Bot Let s start writing some Python The following code imports the necessary modules and uses Python s version of input raw input to get a starting point to which I ve prepended the http found in every web address It then initiates a browser with air quotes with mechanize Browser This code in its final c
245. ping In languages like C you must define a variable s type before you declare it like this string x This is a string or int x 5 Note See the Strings section later in this chapter for more information on strings Python knows that x is an int integer when you tell it that x 5 Despite being dynamically typed Python is strongly typed This means it will throw an error rather than allow you to do things like add an int to a string You can also define your own types using classes Python fully supports object oriented programming OOP I ll touch on that later but in short it means you can create an object that may be a mix of integers strings and other types and that object will be its own type Python has several built in data types Numbers Strings Lists Dictionaries Tuples Files and a few others like Booleans We ll visit each of these briefly later in the chapter Moving forward let s try playing with some variables and operations inside of IDLE Typing gt gt gt print x 5 will return 9 however typing gt gt gt x dad 36 CHAPTER 3 INTRODUCING PYTHON results in an error In this vein however typing gt gt gt DAD hello gives you DADhello because to Python adding strings is the same as concatenating them If you d like to make a list enclose it in square brackets gt gt gt y rest 1234 sleep Also a dictionary a type of file made up of asso
246. plugging it makes many of us computer types cringe so let me teach you the true proper shutdown method Open the terminal and at the prompt type sudo shutdown r now This takes the processor through the proper shutdown sequence killing running processes stopping threads and so on When it s finished it should take you back to the black text only startup page if it doesn t actually power down the Pi Once you re at that page it s truly safe to unplug it Summary You ve now been introduced to the Pi installed its operating system and updated it to within an inch of its life You ve also been introduced to the raspi config tool and you have even played a bit with the command line interface CLI It s time to take a look at Linux 13 CHAPTER 2 Linux by the Seat of Your Pants Raspberry Pi uses Linux as its standard operating system so that means if you don t know anything about this awesome OS you re going to have to learn Don t worry Tll try to make this as painless as possible Whatever your preconceptions about Linux are you can probably disregard them Since its inception Linux has always been regarded as the geek s OS associated with images of button up short sleeve shirt clad pencil necks hammering away on a keyboard while the screen fills with text and somewhere deep in the basement a row of tape driven computer hard drive cabinets spin to life See Figure 2 1 In the background a 20 sided die
247. program that uses regular expressions sudo perform as root user J program run program exit quit terminal session Most of the commands listed in Table 2 1 are self explanatory though some require explanation e man Without a doubt this is the most important command If you are unsure of what a particular command does or what parameters flags it uses typing man command into your terminal brings up the Unix manual page with all of the information you d ever want to know When you bring up a page it normally starts with the name of the command followed by a synopsis of its various permutations a detailed description of the command all of its options and flags and what those options and flags do While you re in the manual view just press Enter to scroll and press q to return to the terminal e ls This command lists the files in whatever directory you happen to be in using flags like 1 and a includes information such as file permissions and modification dates When you use the 1 flag the first part of every entry shows as something like this drwxr xr x 18 CHAPTER 2 LINUX BY THE SEAT OF YOUR PANTS e Inthis case this means that the entry is a directory d the Owner can read write and execute files Group members can read and execute files and All Users can read and execute files In most of our work with the Pi you will be the owner of the files so file permissions shouldn t affect you too much There will be tim
248. py from Apress com import os import time from shtix Shtix import Shtix as SHT1x import Rpi GPIO as GPIO from Adafruit BMPO85 import BMPO85 import smbus import math 97 CHAPTER 6 THE WEATHER STATION GPIO setmode GPIO BOARD GPIO setup 8 GPIO IN pull up down GPIO PUD DOWN bus smbus SMBus 0 address Ox1e def def def def def def def def 98 read byte adr return bus read byte data address adr read word adr high bus read byte data address adr low bus read byte data address adr val high lt lt 8 low return val read word 2c adr val read word adr if val gt 0x8000 return 65535 val 1 else return val write byte adr value bus write byte data address adr value checkTemp dataPin 11 clkPin 7 shtix SHTix dataPin clkPin SHT1x GPIO BOARD temp shtix read temperature C temp temp 9 5 32 if you want degrees F return temp checkHumidity dataPin 11 clkPin 7 shtix SHTix dataPin clkPin SHT1x GPIO BOARD humidity shtix read humidity return humidity checkBarometer bmp BMPO85 0x77 pressure bmp readPressure pressure pressure 100 0 return pressure checkWindSpeed prev input 0 total 0 totalSpeed 0 current time time CHAPTER 6 THE WEATHER STATION for i in range 0 900 input GPIO input 8 if not prev input and input total total 1 prev input i
249. r information storage and retrieval electronic adaptation computer software or by similar or dissimilar methodology now known or hereafter developed Exempted from this legal reservation are brief excerpts in connection with reviews or scholarly analysis or material supplied specifically for the purpose of being entered and executed on a computer system for exclusive use by the purchaser of the work Duplication of this publication or parts thereof is permitted only under the provisions of the Copyright Law of the Publisher s location in its current version and permission for use must always be obtained from Springer Permissions for use may be obtained through RightsLink at the Copyright Clearance Center Violations are liable to prosecution under the respective Copyright Law ISBN 13 pbk 978 1 4302 6424 8 ISBN 13 electronic 978 1 4302 6425 5 Trademarked names logos and images may appear in this book Rather than use a trademark symbol with every occurrence of a trademarked name logo or image we use the names logos and images only in an editorial fashion and to the benefit of the trademark owner with no intention of infringement of the trademark The use in this publication of trade names trademarks service marks and similar terms even if they are not identified as such is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights While the advice and information in this book are b
250. r station anemometer see Anemometer barometer see Barometer bits 95 96 breadboarded chips 96 digital compass 90 91 final code 97 99 I2C Protocol see Inter Integrated Circuit I2C or IIC parts 82 RPS see Revolutions per second RPS temperature humidity sensor see Temperature humidity sensor Web bot bot etiquette 68 command line downloading tool 70 DANE ELEC 74 flash drive 74 HTML 69 IEEE networks 74 information 67 legitimate file formats 73 parsing web pages 71 72 Python modules see Python modules spider 68 TCP connection 70 visual map internet 67 webbot py 79 web communication protocols 69 White Star 68 Wii nunchuk adapter 179 180 I2C or IIC 179 181 LED test side project 183 185 reading 182 sub motors and camera H bridges 185 motors and motor controller 186 187 motor values and settings 186 testing 181 Wire strippers robotics needle nosed pliers 54 pre sized holes 55 version 1 and 2 54 55 231 Learn Raspberry Pi Programming with Python Wolfram Donat Apress Learn Raspberry Pi Programming with Python Copyright 2014 by Wolfram Donat This work is subject to copyright All rights are reserved by the Publisher whether the whole or part of the material is concerned specifically the rights of translation reprinting reuse of illustrations recitation broadcasting reproduction on microfilms or in any other physical way and transmission o
251. r tripped send text Magnetic sensor take pic magnet time stamp time now main body raw input Press enter to start program n GPIO add event detect 11 GPIO RISING callback motion callback GPIO add event detect 13 GPIO RISING callbacksemagnet callback GPIO add event detect 15 GPIO RISING callback limit callback pressure switch ends the program you could easily add a unique callback for the pressure switch and add another switch just to turn off the network try print Waiting for sensors GPIO wait for edge 19 GPIO RISING except KeyboardInterrupt GPIO cleanup GPIO cleanup Summary In this chapter you learned about what sensors are the concept of a sensor network and how to hook different sensors to your Pi s GPIO pins You set up the limit switch pressure switch magnetic sensor and motion sensor which we also use in the Pi powered cat toy in the next chapter With the knowledge you ve gained here you now have the ability to create a full sized security system with its breadth limited only by the amount of sensors you have and how much wire you ve got to put them all together 126 CHAPTER 9 The Cat Toy Most people are pretty familiar with the cat chasing the little red dot paradigm It s so popular it even had a short scene in one of the Shrek movies Some cats will chase the laser spot until they drop Some will only chase it for a little while In any event anyone w
252. ra libraries you can import into your script that add to Python s native functionality In this respect Python is much like Java if you want to do something chances are very good that a library exists to make it easier For example if you want to parse text such as web pages you can check out the Beautiful Soup module Need to log in to a remote computer and you will with some projects Import the telnetlib module and everything you need is available And for numbers the math module has all sorts of mathematical functions that add to Python s number functionality You can try it for yourself in an IDLE session type gt gt gt abs 16 and you should get the result 16 That s because the absolute value function I discuss the topic of functions in its own section later in this chapter is already contained in Python s default libraries However typing gt gt gt ceil 16 7 will return an error because the ceiling function is not in those default libraries It must be imported Now type gt gt gt import math gt gt gt math ceil 16 7 and the terminal will return 17 0 the ceiling of x or the smallest integer greater than x While you may not need to use the ceiling function simply importing the math module gives you all kinds of extra functionality such as logarithmic and trigonometric functions and angular conversions all with just one line of code 39 CHAPTER 3 INTRODUCING PYTHON Strings In Pytho
253. reating and Using Random Numbers You d think creating and using random numbers would be simple Just call a function get a random integer and proceed While that may be how it works in practice and is all that most of us think of the actual process of randomizing output is fascinating it s actually the subject of intense study by many computer scientists and mathematicians See the sidebar Oh the Randomness To get a random number in Python you can use several built in functions The first is appropriately enough the random function The random function returns a float a floating point decimal number It takes no parameters returning instead a random number between 0 0 and 1 0 This is often very useful but for our purposes we re going to need somewhat larger numbers preferably in an integer format which can be done with the randint function OH THE RANDOMNESS Since ancient times humans have had many methods for generating random numbers from flipping a coin to rolling a die to shuffling a deck of cards And for most applications any of these would be fine for generating a random number or set of numbers If you need to decide who kicks the ball first you can flip a coin choosing one card out of a deck of 52 is random enough to make it very impressive when a magician successfully guesses its identity However there are two main issues with using these methods to generate random numbers for any true mathemat
254. repeats the process 182 CHAPTER 12 THE SUBMERSIBLE Because it involves reading and writing to the I2C bus you ll have to run it as root so type the following sudo python nunchuktest py As soon as the script starts it will show you a running status report of all the nunchuk s sensors updated in real time and formatted like so Jx 130 Jy 131 Ax 519 Ay 558 Az 713 Bc False Bz False With the script running try moving the joystick pressing the buttons and shaking the nunchuk to watch the values change You now know how to read values from the nunchuk which we re going to use to drive the motors The Nunchuk and LED Test Side Project As a little side project and as a test for my nunchuk reading ability I hooked up six LEDs to a small breadboard and some GPIO pins so that they would light up depending on which way I moved the joystick or pressed the buttons This might be a worthwhile test to conduct to make sure that not only are you reading the values but that you are able to do something with those values In this case choose four GPIO pins and set them as outputs Connect those pins to a resistor and the positive leg of your LEDs connected in parallel as shown in Figure 12 6 tie all the grounds together and run the following script import smbus import time import RPi GPIO as GPIO GPIO setwarnings False GPIO setmode GPIO BOARD set pins GPIO setup 11 GPIO OUT GPIO setup 13 GPIO OUT GPIO setup
255. reted and acted upon each time you run them They don t produce a compiled file and the instructions are followed exactly as written If you write sloppy code you get sloppy results For this reason scripting languages can result in slower programs e Programming compiled languages most often run directly on top of the hardware on which they are written When you write and compile a program in C the resulting code is executed directly by the processor on your desktop machine Scripting languages most often run inside another program one that takes care of the compiling step just mentioned PHP a common scripting language runs inside the PHP scripting engine Bash scripts run inside the bash shell which you were introduced to in the previous chapter 31 CHAPTER 3 INTRODUCING PYTHON e Programming languages tend to be more complex and difficult to learn Scripting languages can be more readable are less syntax strict and are less intimidating to nonprogrammers For this reason alone scripting languages are often taught in introductory programming courses in schools and students are not introduced to stricter languages like C or Java until they have mastered the basics of programming However the lines between the two have become so blurred in the past few years as to almost completely make the distinctions between the two disappear To enumerate e While it is true that strict programming languages are compiled and s
256. rger 196 CHAPTER 12 THE SUBMERSIBLE Crack the casing open and use a USB to micro USB cord to attach the USB power out to your Pi s power in Then attach your battery s power to the charger s power inputs and voila You have 5V powering your Pi Once you ve got your power issues sorted you can place everything in the enclosure power on your Pi and seal it up Hopefully you ve got something that looks similar to Figure 12 17 Figure 12 17 Completed submersible Obviously the version of the product shown in Figure 12 17 is unfinished I haven t connected the nunchuk yet but you can see the placement of the motors and the enclosure itself As a final construction photo Figure 12 18 shows the placement of the Pi s camera against the front wall of the enclosure held in place with poster putty 197 CHAPTER 12 THE SUBMERSIBLE Figure 12 18 Pi camera placement in enclosure If you ve followed all the instructions carefully you should now have a Pi powered submersible that you can control from onshore or your boat using a Wii nunchuk Pressing the button on the nunchuk will let you take pictures and you can transfer these to your home computer when you bring the Pi back onboard And what sort of pictures can you take Well if you live in Australia you could take something like you see in Figure 12 19 198 CHAPTER 12 THE SUBMERSIBLE Figure 12 19 Underwater photography Full disclosure h
257. ri rap D m 189 Constructing Ahe SUD mere Ree ett caeci cm a a 191 Building the Frame eC 192 Creating the PiS EnclOSUEe cocer eterne reete Dateien er an Du ekaabo Tasa aora t nin 192 Waterproofing the Motor Enclosures scsscssssssesessesseeseseeeseeseasseseeeeeeasseeeesaeseseeasaeseseeesasaeseeesasaeseneeatansesaes 193 Connecting the Nunchuck eesssssessesseseseseene ene tntn nannten tna ta tein tna te tn tn atate sn tn atate testen atate sn sn snas 196 Assembling the Final Product esesssssseseseseesese nennen eaten diaaa aana tttm enata daadaa 196 SUITING E e SUC P P NR HP 200 xiii CONTENTS Chapter 13 The Gertboard iilii esi niuci e ackn acus docu Dd cus n CE Lagen Cu ve Eua C EUR Scd ERN cus 201 Examining the Board 5 oiii d o ie ce po n Ge I eaa cie Dar E TN eee 201 The GPIO diga EET 202 DUCERE EE 203 A to D and D to A Converters eeeeeeseseeeeeeee ener tnter tnt tenete tenete tenete titre te tete te tete tenens 204 iu 205 The Motor Controller eese EAEE A tette tette 206 Open Collector Diverse ui cucteerisi trace erii arii a Eran rr rr e Ere a un o 207 NNUS ESTERNI 208 Some Example Proj86GIS assesses Has atasa cio aote ontario s dando road siet toad ina dha rand inta 209 Configuring the Preliminary Jumper Setup ssssssssssseseseene nennen entente t
258. rmissions can write and save to it The other two groups may only read the file and execute it If you need to change a file s permissions you use the chmod command which can be done either explicitly or with a binary representation of those permissions If you want to do it explicitly the flags used for each group are u owner g group and o all users For instance if you wanted to change the rwxrwxrwx file to be read only for all users you would enter chmod o wx filename which would change its directory listing to rwxrwxr To do the reverse you would enter chmod o wx filename to restore write and execute permissions for all users If you d prefer to use binary permissions you can do that as well Basically each permission has a value IY 4 w 2 andx 1 You add the integers for each group s permissions and set them that way So a group s rwx permissions would be a 7 and an r x permission would be a 5 You need to set each group s permissions if you do it that way if a file currently has rwxrwxrwx permissions and you want to take away write permissions for the group and all users you would enter chmod 755 filename It can get a little confusing but once you ve worked a bit with permissions it will all make perfect sense In our Samba configuration file you ve set the mask and directory permissions to r xr xr x and rwxrwxrwx respectively which is what we need in order to stream all files in that directory to client
259. rom the code it uses GPIO pins 17 and 18 as outputs obviously if you choose to use the motor controller you can set whatever pins you like to be the motor outputs Using the Open Collector Drivers The open collector drivers on the Gertboard are perhaps one of the most overlooked yet most useful parts of the board That s because they can be used to turn an external circuit on or off using the Pi whatever that circuit may be and whatever voltage or amperage it needs within reason of course In this way they are similar to the motor controller but much more adaptable the motor controller can be used only for motors after all There are six drivers available making it possible to drive six external circuits A good test circuit is simply an LED and a resistor in series Caution You do know to a ways wire a resistor in line with your LEDs right Resistors limit current flow thus preventing an excess of current from burning out an LED Take a small breadboard hook a power source like a 9V battery to it and then connect your LED circuit to a completely different row of inputs Then run the open collector program by typing sudo python ocol rg py select a driver and follow the wiring instructions it prints To test the first driver for example follow these steps 1 Connect the of your 9V to the RPWR pin in the J6 header at the top right of the board 2 Connect the of your 9V to any available pin on the board mar
260. rounding grounds and to alert you if those defenses are breached Unfortunately speaking from experience people give you very strange looks if you drive down the street with your Pi hanging its head out of the window but there s no malodorous gas problem so there s that The upshot The Raspberry Pi has some serious shortcomings but those can be overcome to allow it to watch over your house And since this is a book on the Pi that s what we re going to use Using a Sensor Network The home security system and the weather center in another chapter is based on the concept of a sensor network If a computer is like a brain sensors are like the senses that allow it to gather information from and interact with the physical world Cameras are like eyes reed switches are like fingertips and pressure switches are like toes that have been stepped on by a clumsy dog Robots would be nothing without their sensors and any robot brain for example is entirely dependent on that network of sensors This as a matter of fact is one of the coolest things about the Pi its ability to easily interface with physical things like sensors Most modern desktops and laptops have had all of their interesting ports such as the parallel and the serial port taken away left with nothing but a few lonely USB ports and an Ethernet port This leaves them crippled unable to easily interact with the real world Meanwhile the Pi can be plugged directly
261. rrypi This is the command line interface CLI See Figure 2 2 It tells you that you are the user pi logged in to the machine raspberrypi in the home directory pigraspberrypi File Edit Tabs Help pir aspberr ypi Figure 2 2 The Raspberry Pi terminal 16 CHAPTER 2 LINUX BY THE SEAT OF YOUR PANTS If you were in a different directory the prompt would display that directory such as pi raspberrypi gpio Linux Files and the File System As an operating system Linux is completely built around files and the file system A file is any piece of information be it text image video or other that is identified by a file name and a location That location also called a directory path helps keep each file completely distinguishable from all others because the location is technically part of the file name For example wdonat Desktop MyFiles file txt is different from wdonat Desktop MyOtherFiles file txt File names are also case sensitive which means that file txt is different from FILE txt which is different from File txt There are five categories of files that will become familiar to you e User data files containing information you create such as text files or images e System data files containing information used by the system such as logons passwords and so on e Directory files also called folders which can contain files and other directories Directories contained within
262. rs it could only format a drive up to around 127 GB NTFS formats on the other hand have a theoretical upper size limit of 256 TB with a 64 KB cluster obviously much larger and more applicable to today s larger file and drive sizes File sizes are a common source of confusion with many users setting up a file media server for the first time Table 7 1 will help you make some sense of them 101 CHAPTER 7 THE MEDIA SERVER Table 7 1 Common file sizes Type of file File Type Average Size Song mp3 5 MB Music video mp4 avi mpg 150 MB Standard def movie mp4 avi mpg 750 MB High def movie 1080p mp4 avi mkv mpg 1 5 GB Keep those sizes in mind as you look at your current music and video collection and shop around for a drive on which to store them Also remember 1024 KB equals 1 MB 1024 MB equals 1 GB 1024 GB equals 1 TB Yes you can round to 1000 in most cases it s a binary thing 2 1024 Luckily storage prices are dropping steadily and you can most likely pick up a 2 TB drive for under 150 US Because most drives purchased are preformatted with the NTFS format let s make sure your Pi can read and write to it by installing a program called NTFS 3g Open a terminal and install it by typing sudo apt get install ntfs 3g NTFS 3g is an open source read write NTFS driver program for Linux Android Mac OSX and various other systems It comes preinstalled on most Linux systems but not the Pi as of this
263. s 106 CHAPTER 7 THE MEDIA SERVER Fixing the Apostrophe Bug There s one other thing you may need to edit in the default Samba configuration and it s something that in my opinion you shouldn t have to do but it s a bug and it can mess everything up if you miss it Look through all of the uncommented lines in the file and make sure that there are no lone apostrophes used as possessives in the middle of a line If there are delete them For instance at the bottom of the file there may be an apostrophe in the cdrom section cdrom comment Samba server s CD ROM read only yes locking no path cdrom guest ok yes See it there in the second line The problem is that the configuration file treats everything after the apostrophe as a string literal and it doesn t pay attention to anything contained therein until it comes across another single apostrophe again in an uncommented line to close the string So even if it s not in a section of the config file you think you ll use it still screws up the configuration process Just make the second line in this example look like this comment Samba servers CD ROM and it should work fine after that In my smb conf file there were three apostrophes that had to be deleted before the configuration worked correctly If they re in a commented line preceded by a they re totally ignored by the computer so those you can leave alone Restarting the Sa
264. s where the U S Army employs him as a Simulation Specialist In his spare time he likes to play PC games and occasionally develops his own He has recently taken up the sport of golf to spend more time with his significant other Ivana Although he holds a BA in Political Science from the University of Chicago Chaim is an autodidact when it comes to computers programming and electronics He wrote his first computer game in BASIC on a Tandy Model I Level I and stored the program on a cassette tape Amateur radio introduced him to electronics while the Arduino x Wg and the Raspberry Pi provided a medium to combine computing programming N N and electronics into one hobby xvii Acknowledgments Writing a book may be a solitary procedure but it certainly can t be done without help A lot of work by a lot of people went into this enterprise and they all have my deepest appreciation My thanks to Kevin for keeping things moving smoothly to Anne Marie for figuring out what I was trying to say and to Roger LeBlanc for making it look like I know what I m doing Thanks to Chaim the tech reviewer for making sure the stuff I wrote actually runs and does what it s supposed to And thanks to Michelle for taking notice of me in the first place Last but definitely not least thanks to Becky and Reed This one s for you xix
265. s do just that they warn that while things are still working there may be a problem in the near future ERROR and CRITICAL events happen only when something breaks and CRITICAL normally means that the program can t continue working The default level is WARNING which means that unless you set your logging function differently events given a DEBUG or INFO severity because they are below WARNING will not be logged To see the logging module in action type python to start up a Python prompt and enter the following import logging logging warning I am a warning logging info I am an info The second line will output WARNING root I am a warning while the third line classified as an INFO level will not be output to the console If on the other hand you enter logging basicConfig level logging DEBUG it sets the default level to DEBUG meaning that every event will be logged or output regardless of severity Entering the filename and format as we did earlier sets the log file and how events are written to it Note Logging events is an important skill to know for any programmer if you want to learn about Python s logging module in more depth highly recommend you read the Python documentation at http docs python org 2 howto logging html Formatting a KML File A KML file is a special kind of XML eXtensible Markup Language used by Google Earth to delineate landmarks objects and ev
266. s equivalent before flying your balloon to determine the best time and place to launch Reviewing the Photo Results Unfortunately I can t show you any actual results from the PiBalloon yet as it happens during my maiden voyage the camera on my Pi got twisted and was facing the Styrofoam and recorded no pictures whatsoever However Figure 11 5 shows the sort of image you should be able to record Figure 11 5 Alaskan mountain range photo 2013 by NASA 170 CHAPTER 11 THE WEATHER BALLOON My version of the PiBalloon will be flying again soon check the website for this book for further details and hopefully some better pictures The Final Code This code available as balloon py from Apress com will query the GPS board record and transmit its coordinates and take a picture periodically with the onboard camera import os from gps import import time import threading import subprocess set up variables picnum O gpsd None class GpsPoller threading Thread def init self threading Thread init self global gpsd global picnum gpsd gps mode WATCH ENABLE self current value None self running True def run self global gpsd while gpsp running gpsd next if name main gpsp GpsPoller try gpsp start while True f open position txt w curAlt gpsd fix altitude curlong gpsd fix longitude curlat gpsd fix latitude f write str curAlt feet altitude str cur
267. s small enough and power miserly enough to actually be installed onsite it can take pictures of important moments via its onboard camera and because it s connected to a home network it can alert you when something is wrong Perfect Yes you could get a watchdog In fact that s what many people some would say normal people do But let s take a moment to consider the pros and cons of owning a dog versus owning a Raspberry Pi Then we can start building our home security system with the Raspberry Pi Dogs as Security Dogs Canis lupus familiaris are commonly known as man s best friend and they have been used as watchdogs for nigh on 10 000 years They are descended from the wolf and come in all shapes and sizes from the pint sized Chihuahua to the giant Great Dane One ofthe jobs ofthe dog has long been to protect the home from intruders They are intensely loyal and protective of their human family members and their den and will bark at and even attack intruders To keep up this behavior they require food sometimes quite a lot of it And while they are often cute and cuddly and great at keeping your feet warm on cold winter nights the fact that they have to eat means unfortunately that they have to eliminate as well a stinky undertaking for all concerned Dogs are also incapable of being upgraded The last time I tried to plug a USB cable into my dog she yelped And even though dogs can be very cute when they stick their heads out o
268. s two integers a string and a list You can nest tuples index them slice them and do pretty much everything else you can do with a list So why are there tuples if they re almost exactly like lists The most commonly accepted answer to that is because they re immutable they can t be changed By declaring a collection of objects as a tuple rather than a list you ensure that that collection won t be changed somewhere else in your program It s sort of like declaring something as a const in C if you try to change it later the compiler will give you an error Recall that I talked about files in Chapter 2 so the notion should be familiar to you Python has a built in function open that creates a file object that links to a file sitting in your computer s memory File objects are a bit different than the other types as they are really nothing more than a collection of functions that can be called on 43 CHAPTER 3 INTRODUCING PYTHON those external files Those functions include read write open close and various parsing functions for text files To illustrate the following lines open a file test txt or create it if it doesn t exist already for writing writes a line of text to it complete with a newline escape character and then closes the file gt gt gt myfile open test txt w gt gt gt myfile write hello there text file n gt gt gt myfile close All this happens within whatever directory you happ
269. screen and crawling lines of text When it s finished you ll be greeted with the Software Configuration Tool raspi config This gives you some additional options such as expanding the file system always a good idea changing the user password and even overclocking Select whichever option you d like to change with the arrow keys and press Tab and then Enter to activate your choice Definitely enable the camera because you ll be using it later Overclocking is fine but be aware that it can shorten your Pi s lifetime The raspi config menu allows you to overclock up to 1 GHz but if you want to play it safe and stable don t go any higher than 900 MHz Advanced options include setting a hostname and memory splitting Play with these as you like but definitely enable the SSH access because we ll be using this later as well Remember at this stage you can t really damage anything If you brick your card make it unusable simply use the SDCard tool to reformat it and copy NOOBS onto it again Then you can start fresh Later you may want to be more careful but I ll show you how to back up your card so that you don t lose any of your settings if you do something foolish When you re done playing with raspi config select Finish and press Enter Once Raspbian is installed you ll probably want a normal desktop environment No you don t really need one butIthink we can all agree it s nice to see one especially if you re new to Linux and the si
270. see the USB plug that will be plugged into the Pi The whole setup looks ungainly but it flies pretty well Figure 10 6 An overview of the setup Figure 10 7 shows how attached the GPS unit to the nose of the plane Figure 10 7 A closeup of the GPS unit on the plane s nose 155 CHAPTER 10 THE RADIO CONTROLLED AIRPLANE Figure 10 8 shows how I attached the Pi to the plane s wing Figure 10 8 A closeup of Pi on the plane s wing When you re ready to go and have done all your pre flight checks plug in the Pi and wait 45 seconds for the plane py script to start and for the GPS unit to acquire some satellites Then take off and get some great pictures When you re back home with the Pi log in to it and run the kml conversion script called kml py here That script will open the locations 1log file created by the plane py script parse its text and write all of its included locations into a valid kml file called plane km1 You can then transfer that file to any computer with Google Earth installed When it s loaded onto your computer right click on the file and open the Open with menu Find Google Earth in the program options and click Open as shown in Figure 10 9 156 CHAPTER 10 THE RADIO CONTROLLED AIRPLANE OQO Choose Application Choose an application to open the document plane kmi 4 86 E E ie Applications Q FAVORITES FrostWire Y Preview B Desktop Wi Game Center Gam
271. st value which you can find by typing ifconfig at the command line Open your etc network interfaces file for editing by typing sudo nano etc network interfaces You ll have to use sudo because the file is editable only by the root user You should see a line that reads iface wlano inet dhcp Change that to read iface wlano inet static and add the following below it address 192 168 2 50 or whatever address you want obviously netmask 255 255 255 0 or your netmask network 192 168 2 0 your network s location broadcast 192 168 2 255 your Bcast value from earlier gateway 192 168 2 1 yourrouter s IP address Save the file and reboot your Pi When it comes back online it should have the address you specified double check by running an ifconfig command You now have a static IP address Write it down so you don t forget it Now no matter where you end up placing your Pi in your security network you ll be able to log in remotely to administer it To use the static IP you ll need an SSH server running on the Pi Depending on how you first set up your Pi you might have one running already The easiest way to get your SSH server up and running is to run your raspi config tool by typing sudo raspi config at the command line You ll be greeted with the raspi config screen as shown in Figure 8 2 114 CHAPTER 8 THE HOME SECURITY SYSTEM pi raspberrypi File Edit Tabs Help raspi config 1 Expand Filesystem Ensures tha
272. t But in general scripts can be easier for the novice programmer to learn and they can be just as powerful Yes you can program the Pi in C C and even Java or if you re particularly masochistic in assembly language But now that you know and have seen the difference between programming and scripting languages wouldn t you much rather use Python Using Python to program the Pi means that many people who would never dream of programming a computer can pick up a Raspberry Pi and do something really cool with it like build one of the projects presented in this book without learning a difficult language This is after all why the Pi exists to make programming accessible to more students and for that reason Python comes preinstalled on the Pi 32 CHAPTER 3 INTRODUCING PYTHON The Python Philosophy In the world of scripting languages Python is a relative newcomer to the scene though not as recent as many people believe It was developed in the late 1980s perhaps 15 years after the conception of Unix It was implemented in December 1989 by its principal author Guido Van Rossum He has remained active in Python s development and progress and his contributions to the language have been rewarded by the Python community which gifted him with the title Benevolent Dictator For Life BDFL Python s philosophy has always been to make code readable and accessible That philosophy has been summed up in Python s PEP 20 The Z
273. t gt gt spam and eggs spam and eggs spam and and eggs are concatenated gt gt gt title Meaning of Life gt gt gt for c in title print c Meaning of Life For every character in title print it gt gt gt S spam s o s 2 s a 40 CHAPTER 3 INTRODUCING PYTHON The first 0 and third 2 characters of spam are s and a gt gt gt s 1 3 pa The second through the fourth characters are pa When naming a range of characters in a string the first parameter is inclusive the second is not You can also convert to and from string objects for those times when you have an integer that is currently typed as a string like 45 and you need to square it To do that it s as simple as typing gt gt gt int 4 2 16 You can convert to and from ASCII code format with escape characters like 4d and Xs convert from uppercase to lowercase and a whole host of other operations just with Python s built in string library Lists Lists along with dictionaries are arguably the most powerful of Python s built in data types They are actually collections of other data types and incredibly flexible They can be changed in place grow and shrink on demand and contain and be contained in other kinds of objects If you have experience with other programming languages you might recognize Python lists as equivalent to arrays of pointers in say C As a matt
274. t all of the SD card s 2 Change User Password Change password for the default u 3 Enable Boot to Desktop Scratch Choose whether to boot into a des 4 Internationalisation Options Set up language and regional sett 5 Enable Camera Enable this Pi to work with the R 6 Add fs Basta Add this Pi to the ontana Raspber Information zDUDWO configurat Finish aHa Figure 8 2 The raspi config tool Cursor down to option 8 Advanced Options press the right arrow key to highlight Select and press Return Then cursor down to 4 SSH and again highlight Select and press Return Make sure Enable is highlighted on the next screen Figure 8 3 and press Return pi raspberrypi File Edt Tabs Help Would you like the SSH server enabled or disabled Figure 8 3 Enabling the SSH server 115 CHAPTER 8 THE HOME SECURITY SYSTEM Then back out of the raspi config tool by selecting lt Finish gt and pressing Enter Do a reboot by typing sudo reboot and your SSH server should be up and running You can now remotely log in to your Pi from anywhere If you re using a Windows machine you ll need to download the free tool PuTTY in order to log into your Pi If you re using a Mac or Linux box ssh is enabled already Just use the following command ssh l pi your pi s IP address gt and enter raspberry at the password prompt and you re in With PuTTY enter your Pi s IP address in the box add the username and password and
275. t deeper into whatever it is you re hacking away at Wear Safety Glasses Get a pair of safety glasses or goggles This is not negotiable if you don t have a pair get one before you do any experimenting Your sight is too important to lose it to a flying speck of metal from your wire snips or a spark from your grinding wheel If you have a pair that is uncomfortable get another pair you re more likely to wear them if they re a comfortable fit I prefer the safety glasses but many people prefer the goggles that hold fast to your head with an elastic band since they won t fall off Whichever you prefer take care of them to avoid scratches and breakage and wear them when you re working Fire Extinguishers at the Ready Let me tell you a little story When I was building my first little mobile robot with the Pi I was using a Lithium Polymer LiPo battery for the first time It was a small 11 1V 1300mAh battery I was connecting it to my servo motors and I managed to short the negative and positive terminals together with an alligator clip Immediately after the loud pop and the spark the pack began to heat up incredibly fast and the packaging started to swell Thinking as fast as I could I managed to disconnect the alligator clips dropped the pack onto the middle of the floor and threw a glass of water onto the battery I narrowly managed to escape an explosion and I found out later that those LiPo batteries pack quite a punch The mora
276. t gets logged and give the format of each line We ll save each GPS call in three strings the longitude latitude and altitude the three coordinates used by Google Earth They re actually saved as floats not strings which means that we ll have to convert them to strings when we write them to the log file To write a line to the log file the format is simply this logging info logged message or string or what have you 148 CHAPTER 10 THE RADIO CONTROLLED AIRPLANE It is not necessary to use the newline Vn character because each time you call the logging info function it begins on a new line In case you re wondering yes we could simply write the GPS data to a regular file but logging is an important useful concept that many programmers either don t fully understand or skip over completely In the case of Python s logging module you can set log entries to be entered depending on the severity of the event being tracked There are five severities possible DEBUG INFO WARNING ERROR and CRITICAL THE FIVE SEVERITIES LEVELS While I m using the term severities to describe log entries perhaps levels might be a better term When a program executes no matter what language it s written in it normally generates events that can be logged by the logging module DEBUG events are detailed and are usually used only to diagnose problems INFO events are confirmations that things are working correctly WARNING event
277. t in your standalone circuit Then you can replace the chip on the board with another one from Atmega costing about 3 burn the Arduino bootloader onto the chip and go on programming You don t have to use an entire Arduino every time you design a new circuit 217 CHAPTER 14 THE RASPBERRY PI AND THE ARDUINO Installing the Arduino IDE on the Pi Installing the Arduino IDE on the Pi is a simple matter of opening a command line and typing sudo apt get install arduino You ll be prompted to accept all of the necessary dependencies and then the IDE will download and install When it finishes you ll need to install pyserial a Python library that makes it easy to communicate with the Arduino through a serial interface Open Midori your Pi s Internet browser and browse to http sourceforge net projects pyserial Click the Download button and save the file It s a gzipped tar file which means you ll have to unzip and untar it Back in your terminal window browse to the file s location and unzip untar it by typing gunzip pyserial 2 7 tar gz tar xvf pyserial 2 7 tar You ll have a new folder called pyserial 2 7 Navigate into that folder by typing cd and install the library by typing sudo python setup py install Note The process described in this section is routine when installing a Python based library setup py is a common script used to install a Python library like this and it requires the install parameter to run If yo
278. t is to get the GPS unit up and running with your Pi To do this you re going to install the Python gpsd module and use the Pi s Universal Asynchronous Receiver Transmitter UART pins 7 and 8 The Python gpsd module is part of a larger library of code designed to allow devices such as the Pi to monitor attached GPS and Automatic Identification System AIS receivers with ports to C C Java and Python It allows you to read the National Marine Electronics Association formatted data transmitted by most GPS receivers The UART interface is an old one it s basically a serial RS 232 connection but for our purposes it s all we need It consists of a positive and negative connection for power and transmit and receive pins Start by typing the following line to install the software we ll need to read the GPS gpsd and its associated programs sudo apt get install gpsd gpsd clients python gps This will install gpsd and all of its dependencies and associated programs Next you ll need to set up the Pi to communicate over its UART Tx transmit and Rx receive pins because their default configuration is to communicate with a terminal window To do that first make a copy of boot cmdline txt sudo cp boot cmdline txt boot cmdlinecopy txt and then edit it by typing sudo nano boot cmdline txt Delete the following line console ttyAMAO 115200 kgdboc ttyAMAO 115200 so that the file reads dwc otg lpm enable O console tty1 r
279. t least a little exasperation ahead of time Third Python ignores blank lines and spaces except at the interactive prompt and indented blocks of course and comments This is important because it frees you to make sure your code is readable to other programmers even if that other programmer is you at a later date Note Comments in Python are preceded with a the program ignores anything on that line after it Readability in your code is a big deal expect me to drum that into your head regularly Would you rather attempt to debug the preceding program or something like this x this is a test if x this is not a test print This is not x nor is it a test print 89 2 34 5 else print x and I m glad x str 345 43 2 print there are very few spaces in this program While you can certainly read the second one it s no fun and after hundreds of lines of code with no spaces blank lines or comments your eyes will thank you trust me Look at the difference just in the second to last line if you use spaces print x and I m glad x str 345 43 2 You re allowed to use white spaces use them liberally The last part of the if statement I want to mention is the Boolean operators In a truth test X and Y is true if both X and Y are true X or Y is true if either X or Y is true and not X is true if X is false Python uses the words rather than C or C s 88 or operators Learn these operators they ll
280. tboard Atmega chip 203 204 connected to Pi 202 converters 204 205 digital analogue converters 213 214 GPIO pins 202 203 integrated circuits ICs 201 I O section 205 206 jumpers 208 LEDs 210 212 Microchip 214 motor controller 206 207 motor speeds and directions 212 open collector 207 208 213 Pi s GPIO pins RPi GPIO 209 preliminary jumper 209 210 printed circuit board PCB 201 Raspberry Pi project 201 WiringPi 209 H H bridges 185 HDMI See High definition multimedia interface HDMI port High definition multimedia interface HDMI port 5 7 Home security system description 111 dogs 111 Raspberry Pi 112 sensor network see Sensor network home security system HTML See HyperText Markup Language HTML HyperText Markup Language HTML 69 ICs See Integrated circuits ICs IDLE See Integrated DeveLopment Environment IDLE Integrated circuits 53 Integrated DeveLopment Environment IDLE definition 34 icon 34 typing 36 37 window 35 Inter Integrated Circuit I2C or IIC 82 83 179 I O section 205 206 J K Jumpers Gertboard 208 L LED test side project 183 185 Linux commands 18 21 description 15 kernel 16 LXTerminal icon Pi desktop 21 22 package managers 23 24 Pi CLI 16 files and file system 17 Raspberry Pi terminal 16 root user vs sudo 17 shells 22 23 text editors 24 29 GPIO See General Purpose Input Output GPIO pins GPS data 164 users
281. te tttm enata testen anas 38 Exploring Python s Data Types eeseeesseeeseseeeseeeenen ene netntn enata tnn tna tntn inane testen etate ntn enata tn tn stantes 39 Programming With PVIholi ue oi D teo p ro tn ro po o t Cte alte ci aiti 44 lcm 45 LOOPS 46 lali pni RM RM HR 48 Objects and Object Oriented Programming essen reisen rennen nennen nnn nnn nnn nnn nn nana 49 SUC ex a ed 50 viii CONTENTS Chapter 4 Electronics at 100 MPH 11 eeeeeeeeeerennnn nennen nnn 51 Basic Electricity CONGR NES codeine neanta aa aatan ettet ccu 52 sitos cgit rc 54 EUMNEEER 54 Pli rs and Wire Strippers RERRECRRERCRT 54 Wile dvi 55 d fpe 56 IMAG YU GILG eC E E M 56 HOU GIG GUNN om 57 Assorted GlUes sa cinia dns cin t n rina da n o ni dd a a ad Ra i n dd a 57 MUltilTIeler om coe oen ceo E eere 57 Power Supplies eL 58 Breadboard ccc T E 59 POWER OUI usos isses xa AE Pega dr E vas us E Rx oce O a us ERN Eu Eo a EE Ku rA CA EAE on ACH G AR SERERE EE RE AR SERA ERE Re 61 Shu
282. ted While statements are useful if you re waiting for a particular event to happen like a keypress or a user pressing Q to exit An example of this follows while True var raw input Enter something or q to quit print var if var q break Two details to note about this script first in Python 2 x the command raw input is used to get input from a user In Python 3 x that command has changed to simply input Second remember the break command This command literally breaks you out of the loop you happen to be in So in this case the while portion of the loop makes it go forever but ifthe check var q returns true the script breaks out of the loop and ends the program Functions Functions allow you the programmer to reuse code They allow you to be more efficient In general if you find you need to perform a specific task in your code more than twice that task is a likely candidate for a function Suppose you write a simple program that computes the area and perimeter of a rectangle It asks the user to input the rectangle s height and width and then performs the necessary calculations One the simplest ways to do this is to create a function that takes as input parameters the rectangle s height and width It then prints the rectangle s area and perimeter and returns to the program To do this we use a compound statement block beginning with the def assignment The def assignment is how we define a function wi
283. ted to the Raspberry Pi While your normal desktop machine handles more difficult computing tasks the Pi can handle the light lifting required to download web pages parse their text and follow links to download files Bot Etiquette One factor you need to keep in mind should you build a functioning web crawler is bot etiquette I don t mean etiquette in the sense of making sure that the bot s pinky is extended when drinking high tea Rather there are certain niceties you should observe when you program your bot to crawl sites One is to respect the robots txt file Most sites have this file in the root directory of the site It s a simple text file that contains instructions for visiting bots and spiders If the owner of the site does not want certain pages crawled and indexed he can list those pages and directories in the text file and courteous bots will accede to his requests The file format is simple It looks like this User agent Disallow examples Disallow private html This robots txt file specifies that no bots User agent may visit crawl any pages in the examples folder nor may they visit the page private html The robots txt file is a standard mechanism by which web sites can restrict visits to certain pages If you want your bot to be welcome at all sites it s a good idea to follow those rules I ll explain how to do that If you choose to ignore those rules you can often expect your bot and all visits from your
284. terminal Open the terminal on your Pi s desktop and at the prompt type Python You ll be greeted with the same introductory text as that which opens the IDLE window and the same interactive gt gt gt prompt At this point you can issue the same commands as discussed in the preceding section Running Python Using IDLE and get the same results 37 CHAPTER 3 INTRODUCING PYTHON Running Python Using Scripts The problem with both IDLE and the terminal is that you can t write true scripts As soon as you close the window any variables you ve declared disappear and there s no way to save your work The last method of writing Python in a text editor addresses that problem You can write a full length program save it with a py extension and then run it from a terminal Let s write a very short script using Leafpad the Pi s native text editor Open it from the Accessories menu as shown in Figure 3 3 a Education gt File Manager M Electronics gt E Galculator amp Graphics gt 8 GNU Emacs 23 internet gt Image Viewer m Other A Z Leafpad k Programming gt BB LxXterminal gt System Tools gt Bl Root Terminal Xarchiver Preferences gt Bc i Run Logout Figure 3 3 Opening Leafpad In the resulting window type the following X24 y X 42 print y Save it to your desktop as test py Now open a terminal and navigate to your desktop by typing cd Desktop You can now run
285. th the syntax def functionname firstparameter secondparameter def AreaPerimeter height width height int height width int width area height width perimeter 2 height 2 width print The area is 4 area print The perimeter is perimeter return while True h raw input Enter height w raw input Enter width AreaPerimeter h w 48 www allitebooks com CHAPTER 3 INTRODUCING PYTHON This little program simply takes the numbers you feed it and returns the calculations While this may not be the best example you could just calculate on the fly with less code it illustrates the idea of code reuse With this function no matter where in the program you need to calculate area or perimeter all you need to do is call AreaPerimeter with the two parameters of height and width and it s done for you One point to note here raw_input always returns a string even if you enter numbers That s why the height and width variables in AreaPerimeter must be converted to ints before any calculations can be performed Python s functions are slightly different in a few ways from methods functions and procedures in other languages if you re familiar with other languages For one thing in Python all functions are call by reference Without getting too deep into programming speak this means that when you pass a parameter to a function you really only pass a pointer to a variable not the var
286. that the GPS has a fix on satellites To use the gpsd program you need to start it by typing sudo gpsd dev ttyAMAO F var run gpsd sock in your terminal Then to see the current GPS information start the generic GPS client by typing cgps s It may take just a moment for data to begin to stream to the display but when it does you should see a screen like Figure 11 1 Figure 11 1 The cgps display The cgps client is a generic viewer it simply takes the data the gpsd program is receiving and displays it to the user We won t be using the cgps display it s just a handy way of making sure the GPS unit is hooked up correctly and is working We ll use Python s gps module to communicate with the GPS board 163 CHAPTER 11 THE WEATHER BALLOON Storing the GPS Data For this project you ll be writing the GPS data into a file to be read recorded and transmitted later We could use a logging file for this as we did for the RC plane project but it s also important that you learn to use Python to read from and write to normal files In your terminal start a Python prompt and type f open testfile txt w This opens a file in this case testfile txt The second parameter can be one of the following four values r The file is read only w The file is only for writing Previous data will be erased each time the file is opened a Thefile will be appended to r The file is open for both reading and wr
287. the Arduino For those of you unfamiliar with it the Arduino is a popular implementation of microcontroller technology packaged to make it easy for the layperson to program and do complex interesting tasks with some complex electronics For people who just want to make stuff it s a boon the Integrated Development Environment IDE used to program the Arduino runs on almost any computer the programming language is very much like C and perhaps best of all the board is inexpensive with most Arduino versions costing less than 30 US There are several versions of the Arduino ranging from the tiny Arduino Nano to the much larger Arduino Duemilanove shown in Figure 14 1 and the Mega All of the boards have an Atmega168 or 328 chip as their central processor and they have a serial to USB chip onboard to enable them to communicate with your computer They have a selection of jumpers similar to the GPIO pins on the Pi but most of them are female sockets rather than male pins 215 CHAPTER 14 THE RASPBERRY PI AND THE ARDUINO Figure 14 1 The Arduino Duemilanove Using the Arduino on a regular computer is a simple process beginning with downloading the IDE version appropriate for your computer from the project s main web site www arduino cc Once it is installed you can open anew Arduino program called a sketch and immediately start to interface with hardware connected to the board See Figure 14 2 216 CHAPTER 14
288. the guts and wires from prying eyes and paws The PVC pipe I ve used here is too narrow but a pipe with a larger cross section could easily be fitted with the Pi and all the other guts inside of it making a self contained unit Then you can add a power switch for the outside and it s ready to go That should be it Executing the cat toy py script should now keep your feline friend and quite possibly your human ones entertained for hours It s worth noting that you now have the knowledge and capability to aim and fire laser with your Raspberry Pi Yes it s a measly little laser pointer but the concept can easily be applied to any laser regardless of size or power Any laser Have fun The Final Code This code available on the Apress com website as cat toy py sets up the GPIO output pins seeds the random number generators and then spins the servos and lights the laser in random motions import RPi GPIO as GPIO import time import random random seed set pins GPIO setmode GPIO BOARD GPIO setwarnings False GPIO setup 11 GPIO OUT laser power GPIO setup 13 GPIO OUT X servo GPIO setup 15 GPIO OUT Y servo GPIO setup 19 GPIO IN pull up down GPIO PUD UP itin from IR setup servo pwm p GPIO PWM 13 50 q GPIO PWM 15 50 set both servos to center to start p start 7 5 q start 7 5 def moveServos Turns on laser and moves X and Y servos randomly lightLaser p ChangeDutyCyc
289. the motion sensor When you run the preceding script remembering to use sudo because you re accessing the GPIO pins the LED should light up when you move your hand around the sensor and then it should go out again after a few seconds of nonmovement If it doesn t work check your connections and your parts a burned out LED can cause all sorts of troubleshooting headaches believe me Leave the sensor attached as it is as we ll be using it in our system and let s move on to the reed switch 119 CHAPTER 8 THE HOME SECURITY SYSTEM Setting Up the Reed Switch The reed or limit switch is a useful tool in many situations not the least of which being our security system It s often used by robots to determine the limits of movement whether it s driving into a wall or closing a gripper around an object Its concept is simple the switch is normally open letting no voltage through and it has an armature protruding from the body ofthe switch like a long lever When an outside object presses on the lever it closes the switch sending voltage through the circuit in our case to the INPUT pin on the Pi that s listening for a signal The limit switch we re using is also called a sub miniature snap action switch See Figure 8 7 Figure 8 7 The limit switch The long arm protruding from the body of the switch allows objects that are far away to close the switch s contact the small hump protruding from the switch It has three ter
290. the top Y axis servo Constructing the Laser Mechanism We re going to use a standard laser pointer but we re going to modify it in a few important ways The most important way is that instead of using batteries we ll power it using the Pi s GPIO pins This is important because it enables us to turn the laser on and off programmatically rather than fussing with the push button switch To modify the laser pointer you ll need some electrical tape and a flat headed screw about two inches long and with a head just a tad smaller than the inside diameter of the laser pointer Wrap the screw with the electrical tape so that it fits snugly inside the pointer If necessary when you re done cut the end of the tape as shown in Figure 9 5 so that the screw s point is exposed Figure 9 5 Screw mechanism for laser pointer 135 CHAPTER 9 THE CAT TOY Remove the laser pointer s base and take out the batteries Push the screw head first into the body of the pointer so that the screw head is pushing down the inner spring that is normally held down by the batteries You may have to play with the amount of tape you use to wrap the screw you want it to be a tight enough fit to press down the spring and stay in place without danger of moving We also need to tape the laser pointer s power button down so that it s always on As I said we ll be taking care of powering the pointer from the Pi Wrap a piece of tape around the pointer to hold down
291. the work do with my Pi is headless 1 SSH Secure Shell into it or run a VNC Virtual Network Computing server if need to see the desktop but ordinarily don t have a monitor mouse or keyboard connected to it This works well if you re connected to your home network for instance but what if there s no network around Luckily setting up a wired ad hoc network between your Pi and a laptop is pretty simple An ad hoc is simply a network connection between the Pi and another computer such as your laptop with no router or hub in between The easiest way to set this up is to take note of your Pi s static IP address and adjust your laptop s Ethernet port to communicate with that address Let s say your Pi has the address 192 168 2 42 Use a short Ethernet cable to connect your Pi directly to your laptop s Ethernet port Now go into your laptop s network settings Chances are your computer is set up to receive an address automatically from the router via DHCP Dynamic Host Control Protocol Change that method to Manual and give your computer s network port an address that coincides with the Pi s subnet In our example a good address would be 192 168 2 10 If there are spots for it fill in the subnet 89 CHAPTER 6 THE WEATHER STATION mask 255 255 255 0 will work in this instance and the default gateway 192 168 2 1 in this case If necessary reboot your computer or restart your network manager You should now be able to log in to your d
292. ties when it comes to text editors There is a standard editor installed on most distributions called gedit Not only is it rather lightweight itis also not included on the Pi The Pi s built in text editor Leafpad is decent And you may also find yourself getting comfortable with nano another text editor that is pre installed on the Pi and has a very intuitive interface But if you do any serious programming work on the Pi you may eventually want to upgrade to one of Linux s two powerhouses vi or emacs Both vi and emacs are not only powerful editors they can be used as IDEs Integrated Development Environments as well with keyword text coloring syntax highlighting and word completion Both are extensible and customizable emacs for instance has over 2 000 built in commands while vi can be customized with its many ports and clones In fact one of vi s clones Vim Vi Improved is included with almost every Linux distribution and is the one Tl discuss here because it is more of an IDE than its predecessor vi Emacs can be user programmable with Lisp extensions but there is a clone of vi for every sense of aesthetic you may have There is however a sort of war going on between emacs and Vim Linux and Unix users strongly prefer one or the other and they will get surprisingly animated when discussing arguing the pros and cons of each As a conscientious writer I will introduce you to both programs here but as a die hard emacs user I will
293. tntn enata tn tn enata te tnit enata tnit enata testen snae 107 Restarting the Samba Service scscsscsssssceseessseeseseseeeeeeecaeseseeecasseseeeeasseseaeasaeseseeesaeseeeasaseseeesaseeseeseasaeees 107 Connecting with EInIbU DS Noses acc sca tices ei tas RR RRRR RERUM MEE E 108 Where s Python ccc MEAE CUNO CONNOR LL LE I uL Mm 110 SUITITI GE eters neon Snore tae ee Ed dU 110 Chapter 8 The Home Security System eene 111 BELASTET 111 Raspberry Pias SECUTI cv sui duas DNI uiu eua umane NGAI ihe uu DE oe aati Ue 112 USING a Sensor NBDWOIK ctt oot toc Las d oS Lao tol tel tlhe tats 112 Understanding a Pulldown Resistor eessssssessseeeseseeeen ene tetn tnn tnnt ente tntn enata tn tn tnnt 112 A Shopping List of Parts cote rti rette re icone eee eret e ree ra e Re eo ve ne e eene Pu Es 113 Connecting to Your Network Wirelessly eeeseeeeeeeeeeeeeeetnene entente netten tnter annnm tn snae 113 Accessing the GPIO PIFIS 5 1 cuire tenerse tr cicer a RR REC REED CER ROREM ROREM Aaaa 116 Setting Up the Motion S nsOr cccccscccscesscsesseesecssesensesseseeeeesseasseetaccacsecsansacseeraceacsensatsacsecsarsaeaceentaaeaeeetaaeas 118 Setting Up the Reed SWItCh eine tenente testet tnter testet ede taa e o te soe ena Dua ra roc 120 Setting Up the Pressure Switch
294. tour of the Gertboard and its parts and even walk you through some of the programs available for you to use This will give you a working understanding of what the different components do and show you how to interface with them and in turn give your Pi another interface to the physical world Examining the Board The Gertboard is an impressive PCB printed circuit board It measures 13 2 by 8 4 cm 5 1 by 3 3 inches for you American folks and about 1 4 cm 1 2 inch high when it s sitting on its included plastic supports Those supports are designed to allow it to sit on top ofthe Raspberry Pi with its female GPIO headers interfacing precisely with the Pi s male pins as shown in Figure 13 1 201 CHAPTER 13 THE GERTBOARD t Raspberry Pi Gertboord 721 Det 2012 Figure 13 1 The Gertboard connected to the Pi Starting from where it interfaces with the Pi and moving clockwise let s take a short tour around the board to identify what all of those pins and buttons are for shall we The GPIO Pins As a quick reminder the Pi s GPIO pins the row of pins next to the SD card on the Pi are the easiest way to allow it to interact with the world with ground pins both 3 3V and 5V pins and assorted pins that can be configured as either inputs or outputs to read switches and drive motors for instance See Figure 13 2 202 CHAPTER 13 THE GERTBOARD H H H E E i LG GG X d X 3 5 PE mTummvTimnmmnmmmr
295. ts one of which is for your wireless USB dongle That means you re going to need a hub Performance can get sticky when you add a hub because some USB hubs have been shown to work much better than others when it comes to working together with the Pi Perhaps the most important necessary feature is that the hub is externally powered this will prevent your Pi from having to attempt to provide enough power to whatever power sucking device you ve decided to plug in that day This is a problem that will come up with your wireless USB adapter See the section Using a Wireless USB Dongle In any case if you re unsure whether your hub is compatible and don t have a spare hub floating around the house to try the best place to research the matter is often in the Raspberry Pi forums http www raspberrypi org phpBB3 It s here that users like you have tried umpteen different brands and reported CHAPTER 1 INTRODUCING THE RASPBERRY PI back about which ones work which ones don t and which ones require a little tweaking Luckily hubs are relatively inexpensive If the one you try first doesn t seem to work there s a good chance you ll find another use for it somewhere The one I use is a Belkin F5U407 4 port Ultra Mini Hub shown in Figure 1 4 Figure 1 4 The Belkin F5U407 USB hub However here is where you should do as I say not as I do since it turns out that my particular hub is not externally powered I purchased this one because it was s
296. ts around the world flooded element14 Premier Farnell and RS Electronics with orders to the point that people who pre ordered their Pi such as yours truly had to wait up to six months for supply to catch up with demand Many customers may have been current or former programmers eager to play with a new small powerful computer I first learned to program in BASIC on the Commodore VIC 20 with an impressive 20 KB of RAM in well along time ago But there were and are an infinite number of other uses for the Pi as it says on the Raspberry Pi Foundation s About Us page We ve had enormous interest support and help from the educational community and we ve been delighted and a little humbled by the number of enquiries from agencies and people far away from our original targets for the device Developing countries are interested in the Raspberry Pi as productivity devices in areas that simply can t afford the power and hardware needed to run a traditional desktop PC hospitals and museums have contacted us to find out about using the Raspberry Pi to drive display devices Parents of severely disabled kids have talked to us about monitoring and accessibility applications and there seem to be a million and one people out there with hot soldering irons who want to make a robot www allitebooks com CHAPTER 1 INTRODUCING THE RASPBERRY PI Luckily supply has securely caught up with demand There is no waiting period to buy a Pi anymore an
297. typing cd Now let s get the Pi to communicate with our GPS device Connecting the GPS Receiver to the Pi To get your Pi to talk to the GPS receiver you first need to connect the two To do this we ll use the Python library called gpsd and the Pi s UART Universal Asynchronous Receiver Transmitter interface pins 7 and 8 The Python gpsd module is part of a larger library of code designed to allow devices such as the Pi to monitor attached GPS and AIS receivers with ports to C C Java and Python It allows you to read the National Marine Electronics Association NMEA formatted data transmitted by most GPS receivers 146 CHAPTER 10 THE RADIO CONTROLLED AIRPLANE The UART interface is an old one It s basically a serial RS 232 connection but for our purposes it s all we need It consists of a positive and negative connection for power and transmit and receive pins Start by typing the following line to install the software we ll need to read the GPS gpsd and its associated programs sudo apt get install gpsd gpsd clients python gps Next we need to configure the Pi s UART interface By default it s set up to connect to a terminal window but we need to communicate with the Tx and Rx transmit and receive pins To do that first make a copy of boot cmdline txt by typing sudo cp boot cmdline txt boot cmdlinecopy txt and then edit it by typing sudo nano boot cmdline txt Delete the following portion conso
298. u We only need to change a few settings The size of the configuration file is indicative of how adaptable Samba really is because it s used all over the Internet as both a web server and a file server it s important that users can change it to suit their unique needs Our needs are actually rather simple and thus don t require us to change many things in the program s default settings The first setting we may need to edit is the workgroup The workgroup is simply the domain that the Samba server your Pi will be a part of As a home media server the domain is what Windows calls a workgroup your home network Under the Global Settings change workgroup WORKGROUP to the name of your local workgroup if you have one If you don t have one set up leave the workgroup setting as it is Then change server string to h uncomment the following line by removing the hash tag wins support no and change it to read wins support yes Under the Networking settings change the interfaces line to read 3 interfaces etho wlanO lo Leave the following line as it is bind interfaces only yes A little farther down if it s commented out uncomment security user The last part to change is the Share Definitions section This section is where you list and configure the fields and folders you want Samba to share with others Scroll down to the bottom of that section and add the following lines Media comment Media Drive path m
299. u re installing a module that is system wide in other words one that doesn t require you to be in the same directory to run it inside its unpacked folder you ll most often find a folder called build and a file called setup py You don t need to do anything with the build folder because the setup py script does everything for you Using sudo you ll be changing system level files so you need to execute the script as the root user type sudo python setup py install into your terminal and the script will install the module The library is now available for your use in any Python script To test it we ll have to write some Arduino code Bear with me and I ll walk you through it since it may be new to you Open your Arduino IDE shown in Figure 14 3 and in the sketch window that appears type the following code int ledPin 13 void setup pinMode ledPin OUTPUT Serial begin 9600 void loop Serial println Hello Raspberry Pi delay 1000 218 CHAPTER 14 THE RASPBERRY PI AND THE ARDUINO J Accessories gt amp Education gt W ig Il Electronics c9 Arduino IDE n L4 Graphics gt Q Internet gt ai Other gt P D Programming gt gt System Tools p IDLE Preferences gt Run Logout Figure 14 3 Opening the Arduino IDE on the Pi The first line of this script sets the variable ledPin to a number 13 The following setup function sets pin 13 to be an OUTPUT and then opens com
300. udo kill xxxx where xxxx is the PID you noted earlier That will kill the Python script until you remove its line from rc local and reboot The Final Code The final code consists of two parts the plane program and the KML conversion program 157 CHAPTER 10 THE RADIO CONTROLLED AIRPLANE The Plane Program This portion of the program is what runs while the plane is in the air taking pictures and logging GPS coordinates It s available as plane py from Apress com import os from gps import from time import import time import threading import logging from subprocess import call set up logfile logging basicConfig filename locations log level logging DEBUG format message s picnum 0 gpsd None class GpsPoller threading Thread def init self initializes thread threading Thread init self global gpsd gpsd gps mode WATCH ENABLE self current value None self running True def run self actions taken by thread global gpsd while gpsp running gpsd next if name main if in the main program section gpsp GpsPoller start a thread and start logging try and taking pictures gpsp start while True log location from GPS logging info str gpsd fix longitude str gpsd fix altitude str gpsd fix latitude save numbered image in correct directory call raspistill o home pi Documents plane image str picnum jeg shell True picnum pic
301. ulse width modulation PWM signals To control them you must be able to send PWM signals via whatever mechanism you re using whether it s an Arduino pin serial cable or Raspberry Pi s GPIO pin If you want to set a servo s position you need to send it regular pulses of current 50 times a second is an average pulse speed rather than one long pulse That 50 times a second translates if you re wondering to one pulse every 20 milliseconds ms The length of that pulse moreover is what determines the position of the servo An on pulse of 1 5 ms for example sent every 20 milliseconds will send the servo to the center position Shorter pulses will turn it one direction while longer pulses will send it the other Thus by precisely timing the length of the pulses you send to the servo you can precisely position the servo head The graph in Figure 9 3 illustrates this best 132 CHAPTER 9 THE CAT TOY 0 5 0 5 20 ms p 57 D 5 10 15 20 1 5 1 5 7 20 ms 27 527 D 5 10 15 20 2 5 e 5 e0 ms 12 5 Figure 9 3 Duty cycles of a servo If you want to send the servo to the neutral zero position you send it a 1 5 ms on pulse every 20 ms which can be thought of as a duty cycle of 7 5 Likewise if you want to turn it counterclockwise with a 0 5 ms on pulse it has a duty cycle of 2 5 and a longer 2 5 ms on pulse translates to a 12 5 duty cycle In other words the servo is given a high pulse for 2 5 7 5 or 12
302. umbers letters and symbols A good parsing program not only can re form that data stream into the correct symbols it can read the re formed stream and understand what it reads A web bot needs to be able to parse the pages it loads because those pages may should contain links to the information it s programmed to retrieve Python has several different text parser modules available and I encourage you to experiment but the one I have found the most useful is Beautiful Soup Note Beautiful Soup is named after the Mock Turtle s song by Lewis Carroll 1855 Beautiful soup so rich and green Waiting in a hot tureen Who for such dainties would not stoop Soup of the evening beautiful soup Soup of the evening beautiful soup Beautiful Soup the Python library has gone through several versions as of this writing it is on version 4 which works in both Python 2 x and 3 x Beautiful Soup s syntax is pretty basic Once you ve installed it by typing sudo apt get install python bs4 you can start using it in your scripts Open a Python prompt by typing python and try typing the following import BeautifulSoup If you get an error message that says No module named BeautifulSoup you re probably using the beta version of Beautiful Soup 4 BS4 the default version as of this writing In that case type from bs4 import BeautifulSoup Then continue to type import re doc html head title Page title title he
303. upt to the main program to let it know Hey I ve been tripped over here and performs whatever function we want it to In this way we can be sure we won t miss an important button press or switch trip Meanwhile all of the other threads continue their holding pattern At the bottom of this pattern one switch functions as a base if that one switch is tripped you can end the program Otherwise it continues inside a while loop This callback feature is accomplished using either one of two functions GPIO wait for edge or GPIO add event detect GPIO wait for edge does just that waits for a rising or falling edge on any particular pin and then acts when it detects that edge GPIO add event detect on the other hand waits for a rising or falling edge on a particular pin and then calls the function declared in its parameters You can see them both in use in the final code later in this chapter Just be aware that for each sensor or switch we have a unique callback function one that is unique to that sensor so that we know exactly which switch has been tripped Connecting All of the Bits Now that we ve determined how to use all of the pieces of this puzzle let s quickly go over how to connect everything You ll need to use the Ethernet cable to make all of your connections it s strong easy to work with and mostly waterproof Strip the outer casing to reach the wires inside and chop all but the two or three wires you need to connect e
304. ur Pi from the weird things you re probably going to be plugging into the pins There are series resistors in place to protect the Pi s processor if you mistakenly program the GPIO as an output but leave the input jumper in place Likewise sending 9V to a GPIO pin configured as an input could damage the processor if it weren t for those buffered chips 205 CHAPTER 13 THE GERTBOARD Figure 13 5 The I O section An important detail to remember about the pins on the board is that while they can be configured as inputs or outputs the Gertboard is attached to the Pi and is not an extension of it In other words if you call a pin on the Gertboard an input that means it will take as input a Pi output Likewise an output pin on the Gertboard is output to an input pin on the Pi The Motor Controller The motor controller section of the board shown in Figure 13 6 is especially useful for robotics and other power intensive projects It allows you to control high powered items such as large motors with an external power source While we won t be using this in any of the projects in this book Chapter 12 The Submersible uses an external motor controller If you have a Gertboard it s perfectly acceptable to use it rather than the external controller 206 CHAPTER 13 THE GERTBOARD XXE RE E RR 33 mmmTiTmnnmrmTmm Figure 13 6 The motor controller The two middle screw terminals are where you attach the m
305. us low level programming magic But the Raspberry Pi comes with libraries pre installed that allow you to access the pins using Python C or C Additional libraries also exist if you don t happen to like the official preloaded versions This means that you can connect up to eight servos to the Pi right out of the box enough to control a quadruped robot for example The System on a Chip The most important piece on the board is the chip in the middle also referred to as an SoC or System on a Chip The Pi s chip is a Broadcom PCM2835 with an ARM11 processor running at 700 MHz and a Videocore4 GPU The chip can be overclocked to at least 800 MHz without a problem indeed the latest generation of preloaded SD cards offer an overclocking option right from the raspi config file The fastest of the presets will take your processor up to 1 GHz with an on demand function available to prevent your chip from overheating According to the Foundation the result of all that overclocking equals 52 64 percent faster operations Note For more information on overclocking see the article Introducing turbo mode up to 50 percent more performance for free at http www raspberrypi org archives 2008 What all this means is that the Pi s computing power makes it about equal to a 300 MHz Pentium 2 but with the graphics capabilities of a first generation Xbox Not bad for a system about the size of a credit card that costs less than 50 US It also m
306. ut 11 if not prev input and input print Field changed prev input input time sleep 0 05 and run the script Your terminal will remain blank until you wave the magnet past the sensor You might have to experiment with different distances and speeds My experience is that the magnets have to pass pretty closely to register At that point it will tell you field changed After a little experimentation you ll know just where you ll have to mount the magnet in order for the change in field readings to influence your security system Now you can mount the sensor on one pane of a sliding window for instance and a magnet on the other pane and should the window slide open the magnetic sensor will register the movement of the magnet 122 CHAPTER 8 THE HOME SECURITY SYSTEM Setting Up Pi s Camera Finally one of the features that makes the Pi attractive as a security system lynchpin is its ability to take pictures from a small built in camera While this means that the Pi must be positioned in a strategic location in order to pick up anything interesting the Pi is so small that finding a good place for it shouldn t be a problem In order to take pictures you ll have to have two components working on your Pi the wireless and the camera I discussed the wireless setup earlier the camera can be configured with the raspi config tool if you haven t configured it already Once you ve enabled the camera you have two comm
307. ut pin It has three pins Vcc Gnd and Output The pins are from the left in Figure 8 5 OUT and A nice feature of this particular sensor is that it can use any voltage from 3V to 6V To use and test it connect the pin to the Pi s ground pin pin 6 connect the pin to the Pi s 5V pin pin 2 and connect the OUT pin to one of the GPIO pins To test the sensor and our coding prowess we ll start by setting up the GPIO pins accordingly We can use a simple setup to test our code an LED on a breadboard that will light up when the sensor is tripped Start a new Python script let s call it motion py with nano motion py and enter the following import RPi GPIO as GPIO import time GPIO setwarnings False eliminates nagging from the library GPIO setmode GPIO BOARD 118 CHAPTER 8 THE HOME SECURITY SYSTEM GPIO setup 11 GPIO IN pull up downzGPIO PUD UP GPIO setup 13 GPIO OUT while True if GPIO input 11 GPIO output 13 1 else GPIO output 13 0 That s it for the test code In order to test it first connect the pin on the sensor to pin 2 on the Pi Connect the OUT pin to pin 11 on the Pi Connect the pin to a common ground line on your breadboard Finally connect pin 13 on the Pi to the positive leg of your LED through a resistor and connect the negative leg of the LED to the common ground line You should end up with something like you see in Figure 8 6 Figure 8 6 Testing
308. vered with a solder phobic coating which prevents the solder from flowing between connections and shorting them out This makes soldering headers to the connector a simple process even for inexperienced solderers Figure 12 4 Headers soldered to the Wiichuck adapter You ll make four connections to the Wiichuck positive negative SDA the I2C data line and SCL the I2C clock line You ll connect the positive wire to GPIO pin 1 and the negative wire to GPIO pin 6 Connect the SDA wire to pin 3 and the SCL wire to pin 5 You can see the Wiichuk correctly inserted into the controller in Figure 12 5 179 CHAPTER 12 THE SUBMERSIBLE Figure 12 5 Correct positioning of Wiichuck adapter Caution You should connect the nunchuk to the Pi s 1 pin 3 3V notthe 2 pin which is 5V The reason is that the Wii s nunchuk is designed to run on 3 3V not 5V Although it will work with 5V it can severely shorten the life of the controller Activating the Pi s I2C To use the controller with the Pi we need to activate the Pi s I2C capability which is not enabled by default To enable it you need to edit the Pi s blacklist configuration file which lists modules the Pi does not need to load on startup Modules are normally listed here because although they are available they are not often used Open the blacklist configuration file by typing sudo emacs etc modprobe d raspi blacklist conf Comment out the last two lines to remove th
309. vices so we ll need to configure the Pi to make the I2C protocol work Start by editing the etc modules file by typing sudo nano etc modules and add the lines i2c bcm2708 i2c dev to the end of the file saving it when you re done Then reboot your Pi with sudo shutdown r now The Pi also has an I2C utility that makes it possible to see the devices that are currently connected To install it type sudo apt get install python smbus sudo apt get install i2c tools You may also need to edit your blacklist file if you have one The blacklist conf file is used by the Pi s kernel to prevent it from loading unnecessary modules and it may exist only in earlier versions of the Raspbian OS Later versions don t have any modules blocked See if etc modprobe d raspi blacklist conf exists if it does comment out the following two lines blacklist spi bcm2708 blacklist i2c bcm2708 They are there to prevent the kernel from loading the I2C modules and we need to load those modules so we comment them out Now you can run the I2C utility tool called i2cdetect to make sure everything is working and see what devices are connected Type the following line sudo i2cdetect y 1 which should display the screen shown in Figure 6 2 Bum aux eS aat at ca mn Ciccio ciet e Colonie ITT fel AER pi raspberrypi Documents weather sudo iZcdetect y 1 A 4 5 4 c 3 P S 2 J a D 2 e At MGE
310. way speeds and drug users injecting poppy seeds into their veins The 9V battery electrocution incident took place when a Navy sailor in an attempt to measure his body s electrical resistance stuck the pointed probes of his 9V multimeter into his thumbs making his blood a perfect conductor The current traveled across his heart disrupting his heartbeat and killing him You can read more of the Darwin Awards at their website www darwinawards com Basic Electricity Concepts and he spake and spake thusly There shall be one law and that law is of Ohm and it is that V is equal to I times R OK I know this quote is somewhat cheesy however Ohm s Law is indeed the first thing any electrical engineering student learns and it affects everything you do in electronics It means that the total voltage V measured in volts at any point in a circuit is equal to the product of the current I measured in amps times the resistance R measured in ohms The I stands for Inductance which is why it s an I not a C So if you have a 200 ohm resistor that has 0 045 amps moving through it the voltage across that resistor is equal to 9V Like any good algebraic equation it s interchangeable V IxXR IZV R R V I The other important variable in a circuit is power signified by P and measured in watts Power is equal to voltage times current voltage squared divided by resistance or current squared times resistance If this is confusing
311. weather sudo i2cdetect A 1 4 E 6 7 2 2 3 h 4 QQ 60 60 70 pi raspberrypi Documents weather t Figure 6 9 Viewing the compass I2C address If it doesn t appear double check your connections The other address you see listed in Figure 6 9 0x60 is another I2C device I had plugged into my Pi When it shows up start a new Python script to read from the device We ll use the smbus library s I2C tools to read from and write to the sensor First start a directory on your Pi to keep all of your weather station code together by typing cd mkdir weather cd weather 90 CHAPTER 6 THE WEATHER STATION Now that you ve created a weather directory in your home folder and have navigated inside it type the following code into your new Python script import smbus import math bus smbus SMBus 0 address Ox1e def read byte adr return bus read byte data address adr def read word adr high bus read byte data address adr low bus read byte data address adr 1 val high lt lt 8 low return val def read word 2c adr val read word adr if val gt 0x8000 return 65535 val 1 else return val def write byte adr value bus write byte data address adr value write byte 0 0b01110000 write byte 1 0b00100000 write byte 2 0b00000000 scale 0 92 x offset 39 y offset 100 X out y out xead word 2c 3 x offset scale xead word 2c 7 y of
312. wer doing one simple task A simple call to import threading gives you the full power of threads and all they can do for you What do threads actually do Threads allow your computer to seemingly execute several tasks at once I say seemingly because the processor can still execute only one process at a time but threads allow it to switch back and forth between processes so fast it seems to be executing them simultaneously For more of an introduction to threads see the sidebar in Chapter 10 What we ll do with them in this program is use them to poll the GPS receiver By using a thread our main buffer won t fill up with data as we continue to get data yet we can still log the data in our position txt file for later use To use threads in the most efficient way possible we ll create an object called a Poller that will request information from the GPS receiver every 15 seconds using the gps module Every time we get a position reading we ll update the text file and take a picture Note Fora refresher on objects classes and object oriented programming see the sidebar in Chapter 10 Our thread object will be defined like so class myObject threading Thread def init self function used to initiate the class and thread threading Thread init self necessary to start the thread def run self function performed while thread is running From the main portion of the program we can start the thread by declaring a new myOb j
313. with relevant information such as the time and place of the launch predicted altitude balloon description and forecast of the landing location The FAA also requires you to keep track of the balloon s location and have the ability to update the FAA with that information should it be required Regulations differ for moored versus free balloons for more information see the full regulations at http www gpo gov fdsys pkg CFR 2012 title14 vol2 pdf CFR 2012 title14 vol2 part101 pdf A Shopping List of Parts Like the RC plane this is one of the more expensive projects in the book if only because weather balloons can be sort of expensive and you ll need to purchase or rent a tank of helium from a party supply store or welding supply house Here s what you ll need e Raspberry Pi with camera board e LiPo battery and 5V regulator to power the Pi e Latex weather balloon 6 7 foot diameter e GPSreceiver https www adafruit com products 746 161 CHAPTER 11 THE WEATHER BALLOON e Antenna for GPS optional https www adafruit com products 851 e Handheld AM FM radio e 10 foot length of wire e Small Styrofoam cooler e Model rocket parachute e Hand warmers e Fishing line at least 5000 yards e 1 foot surgical tubing about 1 inch I D e Helium about 250 feet e Ducttape electrical tape rubber bands zip ties Setting Up the GPS Receiver As with the RC plane project in Chapter 10 an integral part of this projec
314. with 50 different username password combinations and then fill out an address form afterward mechanize is your tool of choice Another nice thing about it is that it does much of the work such as initiating TCP connections and negotiating with the web server behind the scenes so that you can concentrate on the downloading part To use mechanize in your script you must first download and install it If you ve been following along you still have a Python prompt open but you ll need a regular command line interface for this download and installation process Here you have two options you can exit from the Python entry mode or you can open another terminal session If you prefer to have only one terminal session open exit from the Python prompt in your current window by typing Ctrl d which will return you to the normal terminal prompt On the other hand if you choose to open another terminal session you can leave the Python session running and everything you ve typed so far will still be in memory Whichever option you decide from a command line prompt enter wget http pypi python org packages source m mechanize mechanize 0 2 5 tar gz when that s finished downloading untar the file with tar xzvf mechanize 0 2 5 tar gz and navigate into the resulting folder by typing cd Then run sudo python setup py install Follow any onscreen instructions and mechanize will be installed and ready to use 72 CHAPTER 5 THE WEB BOT Pars
315. working power supply hub monitor mouse and keyboard you re ready to start setting up your Pi The Pi Operating System The Raspberry Pi s default operating system OS the one it s designed to use is Linux If you re not familiar with the Linux operating system don t worry we ll peek under the hood in Chapter 2 For now though know that Linux comes in several flavors or distributions Ubuntu one of the most popular Debian Mint Red Hat Fedora and a few other more obscure varieties The Pi uses a version of Debian called appropriately enough Raspbian Because the Pi doesn t have a hard drive you must download and copy a disk image to an SD card That image is what the Pi will use to boot and it will also act as memory RAM Almost any size will do as long as it s at least 2 GB and more than 4 GB is preferred if you plan on loading any appreciable amount of extra software onto the card You do As mentioned earlier cards up to 32 GB have been tested beyond that your results may be kind of sketchy It s recommended that you use a brand name card and it should be a class 4 which denotes the speed of the card CHAPTER 1 INTRODUCING THE RASPBERRY PI Formatting the Card Your first task is to format the card so that your Pi can read it Insert the SD card into your computer and do the following e For Windows users Download the formatting tool program from the SD Association at https www sdcard org downloads for
316. workshop well ventilated because you ll most likely be sanding painting sawing and doing various other activities that can fill the air and your lungs with dangerous substances You may not be painting enough to be too worried about paint fumes but you ll definitely be around solder fumes for instance Solder contains lead not much but some and lead is poisonous If you come into contact with too much of it too often it can lead to lead poisoning Symptoms include abdominal pain confusion headache and irritability In severe cases it can lead to seizures and even death neither of which facilitate further robotics experimentation Even though you re unlikely to come into contact with enough lead to poison yourself while soldering be aware that it is toxic Don t breathe the fumes and wash your hands thoroughly and often after touching soldered parts You should work in a well ventilated area with windows open or at least a fan going Some experimenters hook up an old computer fan to a dryer vent hose for a customized smoke away solution Organizing Your Workplace As you progress in your experimenting endeavors by buying additional tools parts chips boards and so forth you re going to need a way to organize it all Keeping your work area organized could just as easily fall under safety since having everything stored neatly in its place can eliminate workplace hazards as well At the very least buy several sizes of sandwich ba
317. xercise Navigating in the Linux File System Let s practice moving around Linux s file system with the command line in the following introductory exercise Start by opening a terminal prompt command line prompt by double clicking the LXTerminal icon on the Pi s desktop which is shown in Figure 2 3 LZTerrninal Figure 2 3 The LXTerminal icon on the desktop When it opens make sure you re in the home directory by typing cd and then type pwd The terminal should print out home pi Now make a directory by typing mkdir mydirectory and then without entering it make a subdirectory within it by typing mkdir mydirectory mysubdirectory If you now type Is you should see mydirectory listed as an available directory You can now type cd mydirectory mysubdirectory and you ll be in your newly created subdirectory 21 CHAPTER 2 LINUX BY THE SEAT OF YOUR PANTS Let s test the echo function In the terminal type echo Hello world and the terminal should respond with Hello world True to its name echo merely repeats the arguments you give it However you can echo something to other output formats as well the default simply happens to be the screen For instance you can create a text file by using echo and the gt operator Type echo This is my first text file gt file txt If you then list the contents of your directory by typing 1s you ll see file txt listed Go ahead and create another text file called f
318. xes can receive media files as well as your collection of Macs and Linux boxes It is preinstalled on many Linux distributions the Pi however is not one of them Installing it is as simple as typing sudo apt get install samba SAMBA AS A LIAISON Once upon a time computers all played nicely together Networking was uncomplicated and computers communicated easily over phone lines with low baud rates and small messages If you needed to talk to another computer chances are it was over a BBS Bulletin Board System and it didn t matter what operating system you were using If you weren t using a BBS chances were that you were running DOS as an operating system as was the computer to which you were speaking It was a simpler time Then as computers got more complex different operating systems arose On one side of the dividing wall was the Unix empire with its smaller kingdoms of Linux Mac and BSD On the other side of the wall was the great Microsoft empire beginning with the great King DOS and followed by his heirs the Windows models from Windows 1 01 to today s Windows 8 1 A relative peace existed between the kingdoms in fact the two sides rarely spoke so there were no hostilities As the Internet and other interconnected networks grew however it became necessary for the two sides to exchange files smoothly and without errors The Unix empire being the smaller of the two adjusted all of its operating systems to easily become
319. xt for example the directory name in images picture1 html is images So the first step is to iterate through the linkText again looking for slashes the same way we did to get the base of our web site name like this slashList i for i ind in enumerate linkText if ind directoryName linkText slashList O 1 slashList 1 The preceding code creates a list of indices at which slashes are found in the linkText string Then directoryName slices linkText to just the part between the first two slashes images picture1 html gets cut to images from our earlier example The first line of that snippet bears some explanation because it s an important line of code linkText is a string and as such is enumerable that is the characters within it can be iterated over one by one slashListisalist of the positions indices in linkText where a slash is located After the first line populates slashList directoryName simply grabs the text contained between the first and second slashes The next two lines simply check to see if a directory exists that matches directoryName if it doesn t we create it if not os path exists directoryName os makedirs directoryName This completes our downloadProcess function and with it our simple web bot Give it a try by pointing it at http www irrelevantcheetah com browserimages html and asking for either jpg pdf or txt file types and watch it create folders and download files al
320. you a quick and dirty introduction to Python walking you through the process of creating a few scripts running them and along the way learning some of the basics of this powerful language I ll assume that you have at least a passing knowledge of what Python is and perhaps a slight bit of knowledge of programming but no more than that because let s face it that s why you bought this book Scripting vs a Programming Language Python is a scripting language Some may quibble over whether it s a programming language or a scripting language but to keep the strict technocrats happy we ll call it a scripting language A scripting language differs from a true programming language in a few ways As you read the following comparisons take note of the italics e Programming languages are compiled unlike scripting languages Common languages like C C and Java must be compiled by a compiler The compilation process results in a file of machine code unreadable by humans that the computer can read and follow When you write a program in C and compile it the resulting 0 file is what is read by the computer One of the side effects results of this is that programming languages may produce faster programs both because the compilation only happens once and because the compiler often optimizes the code during the compilation process making it faster than it would be as originally written Scripting languages on the other hand are read interp
321. you can use Python to interface with the Pi and various add ons Well we re going to get to that but before we do I need to explain some other essential prerequisites namely the rules of electronics and electricity tools safety and some how tos They may not be the most sexy topics but any book that deals with building electronics projects should have at least one chapter that deals with concepts like Ohm s Law and How To Solder and the fact that yes it s entirely possible to electrocute yourself with a 9V battery See sidebar Not to mention that I wouldn t want my readers to suffer any bodily injury because I didn t do enough safety instruction So please at least skim this chapter and take some notes if this information is completely new to you If you finish the chapter and feel the need to protect yourself by dressing in a manner similar to Figure 4 1 that is perfectly all right Figure 4 1 Possible lab safety outfit 51 CHAPTER 4 ELECTRONICS AT 100 MPH THE DARWIN AWARDS If you re not aware of them already the Darwin Awards are humorous awards bestowed yearly upon those members of the human race who have managed to remove themselves from the gene pool either through death or sterilization due to their own stupidity Past winners have included thieves electrocuting themselves while stealing copper wire from electrical substations drivers who have switched places with their passengers while driving at high
322. your email and surfing the web but you heard about this Raspberry Pie thingamabob and decided to see what all the ruckus was about Whatever the case may be welcome You re about to join a club not a particularly exclusive one I m afraid since all it takes to join is about 35 US plus shipping but a club nonetheless As a member you ll be able to discuss package managers ARMI1 processors and dot config files intelligently with anyone who will listen You ll know about drivers and APIs You ll become familiar with servos LEDs and cameras on a chip And perhaps most importantly you ll be able to connect to your new mini computer program it in one of many different programming languages though this book deals exclusively with Python build projects and interface those projects with the Pi enabling it to interact with the physical world and do some very cool things With this book I hereby induct you into this club Your experience doesn t matter because I ll take you step by step through the process of setting up your Pi so that you can work with it with a minimum of headaches I ll try to give you a solid background in Linux so that you understand what s going on behind the scenes and I ll devote along chapter on introducing you to Python the scripting language that all the fashionable geeks are scripting in Google uses it NASA uses it and the Book of Faces uses it Let s face it Perl is so yesterday I will also devote a chapter

Learn Programming with

Contents

Download Pdf Manuals

Related Search

Related Contents