The_MagPi_issue_5.pdf

I I S S S S U U E E 0 0 5 5 S S E E P P 2 2 0 0 1 1 2 2

A A M M a a g g a a z z i i n n e e f f o o r r R R a a s s p p b b e e r r r r y y P P i i U U s s e e r r s s

S S t t e e a a d d y y H H a a n n d d F F u u n n

W W i i t t h h T T h h e e R R a a s s p p b b e e r r r r y y P P i i

T T u u t t o o r r i i a a l l b b y y M M i i k k e e C C o o o o k k

A A l l s s o o i i n n t t h h i i s s i i s s s s u u e e

RaspberryPiMediaCentre

AGuideToOpenELECandRaspbmc

SqueezyorWheezy?

DebianDistro'sExamined

http://www.themagpi.com

RaspberryPiisatrademarkofTheRaspberryPiFoundation.

ThismagazinewascreatedusingaRaspberryPicomputer.

WelcometoIssue5,

Thismonthwehaveacollectionofhardwareprojectsforyou,aswellas

ourusualselectionofprogrammingarticlesandgeneraloperatingtips.

WeareproudtopresentanarticlebynoneotherthanMikeCook,who

designedseveralprojectsforTHEMICROUSERmagazine.This

magazinehadagreatinfluenceonmanyofthosewhowerefortunateto

haveaccesstoaBBCmicrocomputer.WithouttheeffortsofMikeand

fellowauthors,theyoungmembersoftheRaspberryPifoundationmay

neverhavethoughtofbuildingtheRaspberryPI.

Wearestilllookingforvolunteerstohelpwithlayoutaswellasauthors

ofnewandexcitingprojects.

AshStone

ChiefEditorofTheMagpi

Ash Stone

ChiefEditor/Administrator/Header

Jason 'Jaseman' Davies

Writer/Website/PageDesigns

Meltwater

Writer/Photographer/PageDesigns

Chris 'tzj' Stagg

Writer/Photographer/PageDesigns

Matt '0the0judge0'

Administrator/Website

Mike Cook

Writer

Duncan Rowland

Writer

Colin Deady

Writer/PageDesigns

Bobby 'bredman' Redmond

Writer/PageDesigns

W.H. Bell & D Shepley

Writers

Colin Norris

Editor/Graphics(CCaveHeader)

Antiloquax

Writer

Lix

PageDesigns/Graphics

Paisleyboy

PageDesigns/Graphics

Andrius Grigaliunas

Photographer

Contents

04 STEADY HANDS

Are you r h an d s stread y en ou g h to beat th e P i ? by M i ke Cook

07 ENVIRONMENTAL MONITORING

Track tem peratu re fl u ctu ati on s. by Du n can Rowl an d .

10 WHAT'S ON GUIDE & COMPETITION

Fi n d ou t wh ere Raspberry J am s' are h appen i n g an d wi n a starter ki t

12 XBMC: Raspbmc and OpenELEC

G et to g ri ps wi th you r m ed i a cen tre setu p. by Col i n Dead y

16 SQUEEZE VS WHEEZY

I m provem en ts an d ch an g es. by J asem an

18 COMMAND LINE CLINIC

Learn h ow to backu p i m portan t d ata. by Bobby (bred m an ) Red m on d

20 C CAVE

Fu n cti on s, poi n ter an d text fi l e en crypti on . by W. H . Bel l & D. Sh epl ey

24 THE SCRATCH PATCH

P rog ram you r own Si m on says g am e. by An ti l oq u ax

26 48HR RASPITHON

Ben , Lu ke, Ryan an d Ed ward recou n t th ei r pyth on ch al l en g e.

27 THE PYTHON PIT

G rad i en t fi l l s, an d u si n g m ath s to pl ot poi n ts of a ci rcl e, by J asem an

32 FEEDBACK & DISCLAIMER

STEADYHANDS

Youdon'thavetogetcomplicatedtogetagreatdealoffun

fromaninterfacingproject.Electricallythisisjustaboutas

simpleasyoucanget,howeverithasaverygoodfunto

technologyratio.

DIFFICULTY: INTERMEDIATE

Steady hands is a very old game, however,

with a Raspberry Pi we can give it a new twist.

The Construction

1. Drill holes in the wooden block for the 'bent

coathanger/wire' just smaller than the

diameter of the coathanger/wire so that the

wire will hold itself up. Make sure to space the

two holes far enough apart to accomodate

your design.

The idea is that you have to guide a wire loop

along a bendy wire without making the two

touch. You can make this as complex or as

easy as you like by having more bends in the

wire or having the loop smaller.

2. Make the wire loop and solder a length of

wire to it. You might want to add a covering of

insulation tape, or better self amalgamating

tape, over the end you hold.

Materials

-Bare single core Wire (2mm Dia)

e.g. Metal coat hanger. If using wire it

needs to be thick enough to hold its shape.

-Stranded wire (insulated)

-Block of wood (size depends on your

design of 'bent coathnager')

-Electrical Tape

3. Put the 'bent coathanger/wire' through the

wire loop and then into the wooden block.

4. Solder a length of stranded wire (insulated)

to one end of the 'bent coathanger/wire'.

Tools

-Drill

-Drill Bit (just smaller than the diameter

of the wire)

-Solder

-Soldering Iron

5. Drill two holes on either side the bent

coathanger/wire as shown in the image below

for the rests.

6. Put two short lengths of coathanger/wire to

act as rests in these holes. These will detect

when the game starts and when the wireloop

reaches the end. Bend them so the loop will

rest against them without shorting out to the

bent wire.

A - Physical pin 7 GPIO pin 4

B - Physical pin 3 GPIO pin 0

C - Physical pin 5 GPIO pin 1

D - Physical pin 6 Ground

7. Solder a length of normal wire (insulated) to

each end stop.

First of all the three lines must be set up as

inputs. They boot up as inputs anyway but it is

always good practice to initialise the lines you

want to use.

8. On each end of the 'bent coathanger/wire'

and both rests, from where they hit the block

of wood, tape them with insulated electrical

tape 4 cm high.

I used the GPIO numbers and not the physical

pin numbers in the code as I strongly believe

that using physical pin numbers is actually not

a sensible thing to do, and not a good way to

teach children. It's like the ITA (Initial

Teaching Alphabet) mistake all over again.

The following table, and image, show how

each part of the 'STEADY HAND' attaches to

which pin of the PI GPIO via the 2.54mm

header:

The game is in three phases:

1) Wait until the loop is placed on the start

rest.

2) Wait until the loop is removed from the start

rest.

3) Time the interval from lifting it off the start

rest until it reaches the end rest. While it is in

this phase monitoring the bendy wire for

touches.

STEADY HAND

PI GPIO

WIRE LOOP

GROUND - PIN 6

BENT WIRE

GPIO 1 - PIN 5

START REST

GPIO 4 - PIN 7

This is then repeated forever, so a control C is

needed to stop the program.

END REST

GPIO 0 - PIN 3

This is just the bare bones of what is possible.

I always think a good way to learn anything is

to extend and modify from a base. This is your

base.

One extension would be to add a sound

whenever the bendy wire is touched. The

August issue of the MagPi showed you how to

incorporate sound effects into a Python

program, so take those bits and graft them

into this program.

Raspberry Pi Physical Pins

You could also keep track of the high scorer,

or even have a table of high scores along with

the names. You can make that permanent by

writing it out to a file and reading the file when

the program first starts up.

How does the GPIO work?

Basically we have three signal wires and a

ground. Using GPIO 0 & 1 means that a pull

up resistor is already connected on the Pi, just

leaving GPIO 4 to have either an external pull

up attached or activating the internal pull up

resistor. I opted for the latter option.

You can add penalty points into the time, say

3 seconds per point to give a single figure. On

a more practical level, see if you can abort a

timed run when the loop is placed back on the

start loop.

There is plenty of scope for adding your own

refinements. Have fun.

The Program

The software was my first venture into writing

in the Python language. It is quite straight

forward.

Continuesonthenextpage

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