Python and the Oracle Client

Installing the python cx_Oracle extension module for connecting to Oracle databases on this Fedora 18 workstation turned out to be a bit of a faff by giving an assortment of unhelpful error messages, if you are having the same pain maybe this will help.

You will need two files from the Oracle Database Instant Client download site, the basic client package and the SDK (devel): http://www.oracle.com/technetwork/database/features/instant-client/index-097480.html For Linux choose the correct flavour for your installed operating system: x86 or x86-64 for 64bit operating systems, you will need to register on the site to access the files. For my purposes I got the 11.2 version for x64 RPM files, install them using:
$ sudo rpm -i oracle-instantclient11.2-basic-11.2.0.3.0-1.x86_64.rpm
$ sudo rpm -i oracle-instantclient11.2-devel-11.2.0.3.0-1.x86_64.rpm

You will now need to tell the system where the libraries are:
$ sudo su
# echo /usr/lib/oracle/11.2/client64/lib/ > /etc/ld.so.conf.d/oracle.conf
# ldconfig
# exit

To install cx_Oracle you will need to set some environment variables otherwise you will get an “error: cannot locate an Oracle software installation” message. The easy_install program is found in python-setuptools I have included it in the recipe as a reminder if you have not installed it already.
$ sudo yum install python-setuptools
$ export ORACLE_HOME=/usr/lib/oracle/11.2/client64
$ export LD_LIBRARY_PATH=$ORACLE_HOME/lib:$LD_LIBRARY_PATH
$ export PATH=$ORACLE_HOME/bin:$PATH
$ sudo -E easy_install cx_Oracle

or by downloading the version from http://cx-oracle.sourceforge.net/ and installing it manually, you will still need to set the exports, as above, and do the following for installation:
$ sudo -E python setup.py build
$ sudo -E python setup.py install

The -E on the sudo takes your environment variables, including the three you just set, into your sudo session.

Success:
$ python
Python 2.7.3 (default, Aug 9 2012, 17:23:57)
[GCC 4.7.1 20120720 (Red Hat 4.7.1-5)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import cx_Oracle
>>> exit()

When the the library cannot be seen, you get this error:
$ python
Python 2.7.3 (default, Aug 9 2012, 17:23:57)
[GCC 4.7.1 20120720 (Red Hat 4.7.1-5)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import cx_Oracle
Traceback (most recent call last):
File "", line 1, in
ImportError: libclntsh.so.11.1: cannot open shared object file: No such file or directory
>>> exit()

Taking Photos on the Canon EOS with an Arduino

For my Spangaly Stick project, more of which later, I have been wanting to add a remote control function for the camera for a while now and with the extended winter I found I had the time. I am using an Arduino micro-controller fitted with an XBee wireless shield to respond to a keyword sent by another Arduino with a similar setup, or from a computer with an XBee on a USB port.

take a picture - board

This board had been built to work with the Canon EOS DSLR range of cameras, but should work with other makes of camera fitted with an electronic remote socket. For basic use the camera should be set in Aperture Priority (Av) mode with the lens set to manual focus and if your using a tripod switch off any image stabilization.

For this project you will need:

  • A Windows (XP and above) Computer
  • An Arduino Uno R3
  • Two XBee’s
  • An XBee USB adapter
  • An XBee Shield for the Arduino
  • A battery to power the Arduino, I use a 12v 1.3Ah Sealed Lead Acid.
  • A remote lead for your camera
  • Ability to solder, read circuit diagrams, etc..

For this remote to work, you will need to configure two XBees to talk to each other. The easy way to do this is using the X-CTU tool (unfortunately it is Windows only) and a XBee USB Adapter. The XBees come in two main types, the Series One (S1) and Series Two (S2) they will need to be of both the same series to talk to each other, I have used Series One bees here, but not the ones without the sticking out antenna as I suspect they may be a bit delicate.

While the XbeeSheid configuration is documented on the arduino site, I shall summarise here. With the XBee plugged into the USB adapter and the adapter plugged into the computer wait for it to be detected by Windows then you can configure it. In X-CTU, on the PC Settings Tab, select the USB Serial Port. By default the XBee is set to baud: 9600, flow: None, data: 8, parity: None, stop: 1. Click the Test/Query button you should see some basic XBee settings, if it says it cannot communicate, try a different baud rate. Higher baud rates are available, but whats the rush?

Now click the Modem Configuration tab, under Modem Parameter and Firmware, click Read, after a pause at the top of the list The modem indicated will be whatever model you have, in my case XB24, select the function set we will be using: XBEE 802.5.4 RS485 ADAPTER and the firmware version: 13E8. You will need to set the Networking & Security Channel (CH) and the PAN ID (ID) to the same on both, as well as check the Serial Interfacing are set correctly, Interface Data Rate (BD): 3 – 9600, Parity (NB): 0 – NONE. Click Write to save the settings to the XBee.

For testing the XBee’s, I had one plugged into the USB adapter and the other placed into the the XBee Shield, an LED fitted across Digital Output 12 and Ground, and sent the following program to the Arduino, remembering to flick the little switch on the shield to USB for programming, and Micro for XBee emissions.

The circuit I made for taking photos includes the focus, this is optional but I have included it so the camera can be woken up before the picture is taken. An ILD74 opto-isolater is used to electrically separate the camera from the Arduino, it also simplified the circuit not having to use transistors. The LED’s are useful additions but are optional.

The diagram also shows the Canon Remote connections. Most use a 2.5mm stereo jack plug, but the more expensive cameras have a proprietary Canon N3 connector, to get the lead you will need to sacrifice a wired remote, one of these can be gotten of ebay very cheaply, about £3.00. The colours for the wires can be anything, so you will need check with a continuity tester.

The program on the Arduino listens for a keyword, in this case ‘PHOTO’ which then triggers the picture taking sequence first by setting the focus to wake the camera up then taking the picture. The Indicator LED is used to show activity on the serial port.

Can a Pi Raspberry?

The Raspberry Pi is a small computer, and as such an obvious but important question occurred to me, and despite Google, I was unable to find an answer. So using science, LEGO, a balloon, and a compressed air supply I set out to discover if the Raspberry Pi could indeed blow a raspberry.

To embark on this scientific discovery, first, I needed to be able to control a motor, for this I built a dual relay board that can be switched using a couple of the Pi’s GPIO pins:

LEGO PF Motor Controller v3

Here is the circuit diagram:

LEFO PF Motor Controller v3

And the Python source code:

To which I connected a large LEGO PF motor. This is used to switch the pneumatic valves via a clutch cog and a large cog. I used a 9v power supply for this, but a PF Battery box can be used, cut an PF extension lead in half, use the light grey side for the motor, and the dark grey end to connect to the battery box. My compressed air supply operates at 2bar / 30 psi, it was built to work with LEGO pneumatics, I found that anything much above that pressure would cause the pipes to pop off the connectors.

The Pi Raspberry Project

Obviously I needed something that would make a sound. For this, a balloon (the sausage type), a small pop bottle, and some more LEGO were suffice. The air is injected into the bottle trough a couple of holes at the rear.

The Pi Raspberry Project

I would like to say thanks to the people on the Raspberry Pi forum for their advice on the electronics: http://www.raspberrypi.org/phpBB3/ and further reading about LEGO PF motors can be found here: http://www.philohome.com/pf/pf.htm, and the raspberry http://en.wikipedia.org/wiki/Blowing_a_raspberry