samedi 30 mars 2013

A first software installation on the Rasperry Pi

Screenshots on Raspeberry Pi

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After we have created our first SD card, booted it and run the setup procudure, we had the need to install the necessary software to make screenshots on the Raspberry Pi itself and to transfer them on a PC for documenting correctly our blog articles here!

The requirement

A Linux tool on our LXDE desktop environment to make screenshots and why not scrot!

Installing scrot

We can use either the terminal console on the Raspberry Pi or the Windows putty.

We should first run an update on our Raspberry Pi:

sudo apt-get update

The scrot application can be installed with:

sudo apt-get install scrot

and we should answer Y for yes to:

Do you want to continue [Y/n]? Y

The program scrot is now install, and we can execute it from putty or from an LXTerminal on the Raspberry Pi:

scrot for immediate snapshot or with scrot -d 5 for instance after a 5 seconds delay usefull for rearranging or closing some wimdows.

The png file is available in the form 2013-...._1360x768_scrot.png which could be transfered to a Windows PC with WinScp.

ssh and scp on the Raspberry Pi from Windows

ssh and scp on Windows for Rasperry Pi 

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  • ssh allows to access the Raspberry Pi from ouside in console mode

  • scp allows to transfer files between the RaspBerry Pi and an external computer

References for installation:

We can select an installer or copy the software directly into a directory we should remember for later execution!

The IP address of the Raspberry PI 

Before using ssh or scp, we need to find out the IP adress using sudo ifconfig:

The IP address is here

ssh (secure shell) with putty

We can start the putty.exe application for instance from the Windows command start:

Here we have already defined a saved session: no need to retype the IP address.

We can now enter the user pi and the password raspberry if we didn't change it in the first setup:

The session is now active and we can now work in the same way as in a terminal session directly on the Raspberry Pi:

Useful commands and configuration:
  • Ctrl-L to clear the content of the window
  • Click on the tittle bar with the right mouse button, change settings..., Window appearance, Font, and for instance Courier 12 points

scp (secure copy) with winscp

We can start the WinSCP.exe application for instance from the Windows command start:

This is the same as for ssh, with the ip address, the iser and the password, and we can save our configuration fpr later use:

When connected we will see the two parts where we can transfer files in one or another direction:

There are many sites on Internet where we can find a number of good descriptions.
This one is particular impressive:

vendredi 29 mars 2013

A first boot on the Raspberry Pi

Booting our SD card on the Raspberry Pi

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After we have created our first SD card, we can now boot our system on the Raspberry Pi.

The material

On the left side, we need to connect an USB mouse and an USB keyboard. The Ethernet cable for accessing the local network and the Web will be required to add more software from the Internet.

On the top we see the HDMI cable connected to a display with HDMI capabilities.

Finally on the left the micro USB cable to get the power for our device and our SD card coming from Preparing the SD card. We decided to use a 4 Gbytes SD card which is about twice the size of the original size, allowing us to have sufficient space for more applications and data.

The first boot

As soon as we boot the system, we should see the display active showing a huge number of progress messages indicating that the Kernel is booting.

At the end this ncurses based raspi-config tool should appear in order to setup the system:

With ncurses, we cannot use the mouse but the cursor keys like up and down on the keyboard, as well as the return key. The left and right cursor keys allow to select the final <Ok> or <Cancel>.

A number of things are absolutaly required at this point:
  • expand_rootfs to extend the system to fill the SD card.
    The extension will be done on the next reboot.
  • configure_keyboard to set the keyboard. If we don't do it, we could have then surprises with characters like y, z, -, _, and other characters, if we don't have an Englisch keyboard.
    A number of varietes of keyboards, like the Generic 105-key and languages will be presented.
    For swiss French keyboard, we need to select first the German (Switzerkand).
    For the AltGr we can keep the default. No compose key too.
    We will allow tu use the Control+Alt+Backspace to stop the X server.
  • change_pass can be done to change the installed user und password which are pi and raspberry.
  • change_timezone is recommended to be on the right place on the planet earth!
  • ssh is a must to be able to access the board later from the PC. We should se the message: SSH server enabled.
  • boot_behavior allows to start the desktop environment and not in console mode.
    We should set it to Yes.   
We can stop the Raspi-config with the <Finish> selection and the return key. A "Would you like to reboot now?" ist presented and we should select agaib <Yes>.

A a later stage, wenn the system has been already partialy setup, we could run again this configuration with sudo raspi-config.

When everything is ready, we can reboot the system to get the Raspian LXDE desktop environment:

mercredi 27 mars 2013

Starting with the Raspberry Pi - SD card

Preparing the SD card

The first thing to do is to get the Linux software and to write it on an SD card.
We can do it actually before getting the Rasperry Pi board and material, and the day we receive it by post, the system could be running after 5 or 10 minutes of impatience!

We will describe here how to do it on Windows and with a 4 Gbytes SD card which is about twice the size of the original distribution, allowing us to have sufficient space for more future applications and data.

Getting the software

The Linux image file can be downloaded from and the Raspbian “wheezy” can be selected, for instance and then downloaded.
The Zip file contains the image 2013-02-09-wheezy-raspbian.img. This is can be extracted and written on the SD card. We will describe here how to do it on Windows.

Getting the win32diskimager-binary software

This Windows application can be found in This is not a traditional Windows installer and needs to be unziped into a subdirectory where we have our Rasperry Pi Windows PC working environment (here for instance D:\Raspberry\win32diskimager-binary\),

When executing Win32DiskImager.exe we get this:

We see now that we need to specify the image file and the drive where a 2 Gbytes SD card has been inserted. Myself I use a cheap USB 3.0 multi card which is faster and particular interesting when transfering picture files from a camera.

When everything is ready we get this:

Using the Windows explorer, we can then decide to rename the CD card for instance to WHEEZYFEB13, to remember later what is on the card, und even to check the content to find out a number of files with the 09.02.2013 date, the creation date of this Raspian Linux.

As usual, we should eject the SD card with the Windows gadget!

More articles:

dimanche 24 mars 2013

Discovering the Raspberry Pi - Part A

A starting point with Raspberry Pi

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After I got this nice project running successfuly, I decided to write in a blog sufficient information to help beginners with Raspeberry Pi to become familiar with its hardware and software. There are already so many articles on the Web doing more or less the same thing .... but why not again and probably differently!

Being able to switch on or off a 220 Volt home appliance using the light level in the room

So many things have been done before reaching this first running project including:
  • Getting the hardware
  • Installing the software
  • Describing all sort of difficulties before getting my bedside lamp reacting on light level changes in the room
  • Adding features inside and outside to extend this project
The idea is also for the author to collect all possible information in order to be able for him, or other interested "players of this Rasperry Pi game", to find out the essential!

The different parts

This is the sensor part to get the light level:

Photo-resistance circuit

This is the relay to switch on a 220V light or anything else connected for instance to a light bulb cable:

220 Volt Relay

And both connected to the Raspberry Pi board:

The code

The following Python code to deal with this project is more or less some copy/paste from different projects, in particular from:

# Reading an analogue sensor with a single GPIO pin
# Set the relay on off according to the light level

import RPi.GPIO as GPIO, time

# GPIO library to use Broadcom mode

# Charge time measument
def RCtime (PiPin):
  value= 0
  # Discharge capacitor
  GPIO.setup(PiPin, GPIO.OUT)
  GPIO.output(PiPin, GPIO.LOW)

  GPIO.setup(PiPin, GPIO.IN)
  # Count loops until voltage across
  # capacitor reads high on GPIO
  while (GPIO.input(PiPin) == GPIO.LOW):
    value+= 1

  return value

GPIO.setup(14, GPIO.OUT)

# Main program loop
while True:
  lum = RCtime(4)
  print lum # Measure level using GPIO4
  if lum < 360:
     print 'High light'
     GPIO.output(14, False)
     print 'Low light'
     GPIO.output(14, True)

The relay

This is the part dealing with the 220V relay. On the picture, we see that 3 cables are connected (one of the 4 is not required):

·        Yellow - the GPIO pin
·        Red - the 5 Volt power
·        Black - the ground

The wire for the 220 Volt goes to the green connector. A 220V extension cord with 2 o 3 (with ground) wires can be prepared like this:

There is a very nice description of the pins in this Web site:

The pin 8, the fourth from the right on the external side:

correspond to the BCM GPIO pin 14 (see the Python code). The pin 2 is the 5 Volt required for the relay.

Testing the relay

This is actually recommended when building a project with different parts.
Here a small program for verifying our relay:

import RPi.GPIO as GPIO, time

print "Start"


PiPin = 14
GPIO.setup(PiPin, GPIO.OUT)

GPIO.output(PiPin, True)


GPIO.output(PiPin, False)

print "End"

There are many different ways to test this relay.
This could be done using C++ or directly accessing the GPIO from a Terminal session.

There is an interesting article with nice pictures here:

The sensor part

The cables required are:
·        Purple - the 3.3 Volt for the power
·        Black - the ground
·        Grey - the GPIO pin to measure the lightsensor

A complete and nice description here:

There is no need to copy/paste it here! 

A view from inside of the pins may help too:

The first pin is the 3.3 Volt and the fourth the GPIO4.

More articles:

And with the Gertboard: