Infra-Red Coin Detector for Arduino

For something I’m building I need have the Arduino detect a coin being dropped trough a slot, for this I have built an IR detector, it comprises of an IR LED, IR Photo-Diode, Op-amp and ATtiny85 micro-controller.

IR Coin Detector (Mk3)

The circuit works by having the IR LED flood the Photo-diode so that when an object passes between them the Photo-diode stops letting current through, this is fed into the op-amp to provide a consistent output for the ATtiny85 micro-controller to detect the change in signal to then flash a couple of LED’s and provide a signal to an Arduino.

IR Coin Detector (Mk3)

Here is a program that flashes a couple of LED’s and makes output pin 4 high:

Sources:

  1. DIY Science: Measuring Light with a Photodiode II
  2. Pin Change Interrupt on the ATtiny
  3. Programming an ATtiny85 with an Arduino

Recording Sound on the Raspberry Pi

The Raspberry Pi does not have a microphone socket, which is inconvenient when you wish to record sound. To fix this you will need a USB Sound Card, for which I bought a Creative Sound Blaster Play! for about £20 and a short USB extension lead as the sound card is slightly too large and blocks the other USB port.

With the latest Raspbian “wheezy” installed on a Pi Model B with 512Mb of RAM and the overclocking set to High in raspi-config, here is a recipe for getting your Raspberry Pi to record sound from the command line. For the test setup I connected my iPod to the microphone port of the sound card, plugged everything in and powered up.

Raspberry Pi Records

After logging into the Pi, check that the computer can see the card, use lsusb to find it, here the card is highlighted in blue:
$ lsusb
Bus 001 Device 002: ID 0424:9512 Standard Microsystems Corp.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp.
Bus 001 Device 004: ID 046d:c52e Logitech, Inc.
Bus 001 Device 005: ID 041e:30d3 Creative Technology, Ltd Sound Blaster Play!
remember that different makes of card will have different names and ID’s

Your user will need to be in the audio group, check this with groups <username>:

$ groups pi
pi : pi adm dialout cdrom sudo audio video plugdev games users netdev input
if not, then add them with:$ sudo usermod -a -G audio <username>

There is/was an issue with the Pi’s USB port that meant it can/could become overwhelmed1 with data which causes popping and bubbling noises to be included in your recordings, this can be fixed with an update of the Pi’s firmware:

$ sudo apt-get update
$ sudo apt-get upgrade
$ sudo apt-get install rpi-update
$ sudo rpi-update

The Raspbian image already has the alsa-utils for sound already installed, the programs I am using for recording and playback are:

  • alsamixer – GUI for setting the recording and playback levels
  • amixer – Command Line for setting the recording and playback levels
  • alsactl – for saving the settings set in alsamixer or amixer to use again after a reboot
  • arecord – For recording the sound
  • aplay – For playing back your recording

All of these programs have a –help option.

There are two methods for setting up the the microphone port on the card, the first is alsamixer:

alsa mixer

$ alsamixerPress F6: Select Sound Card, and choose yours from the list, the bcm2835 ALSA is the on-board sound, for me the one to pick was: USB Device 0x41e:0x30d3 and take a note of the card number, in my case: 1. Now select the Mic and increase the volume to 52, or the first white blob, you’ll need to change it later, but its a good place to start. The Auto Gain Control wants to be off, select the gain control and press M to toggle so it displays [MM] for mute. Press Esc to exit and save the settings with:$ sudo alsactl store 1 where 1 is the card number.

Alternatively, you can use amixer. First find your sound card, in amixer there does not appear to be a method of listing the available cards, but on a Raspberry Pi I guess it will always be card 1, you can list the cards current status with:

$ amixer --card 1 contents
numid=1,iface=MIXER,name='Mic Playback Switch'
; type=BOOLEAN,access=rw------,values=1
: values=off
numid=2,iface=MIXER,name='Mic Playback Volume'
; type=INTEGER,access=rw---R--,values=1,min=0,max=32,step=0
: values=21
| dBminmax-min=0.00dB,max=47.81dB
numid=5,iface=MIXER,name='Mic Capture Switch'
; type=BOOLEAN,access=rw------,values=1
: values=on
numid=6,iface=MIXER,name='Mic Capture Volume'
; type=INTEGER,access=rw---R--,values=1,min=0,max=16,step=0
: values=7
| dBminmax-min=0.00dB,max=23.81dB
numid=7,iface=MIXER,name='Auto Gain Control'
; type=BOOLEAN,access=rw------,values=1
: values=on
numid=3,iface=MIXER,name='Speaker Playback Switch'
; type=BOOLEAN,access=rw------,values=1
: values=on
numid=4,iface=MIXER,name='Speaker Playback Volume'
; type=INTEGER,access=rw---R--,values=2,min=0,max=151,step=0
: values=52,52
| dBminmax-min=-28.37dB,max=0.06dB

So I want to turn the Auto Gain Control off, and the recording volume to 14:
$ amixer -c 1 cset numid=7,iface=MIXER,name='Auto Gain Control' 0
numid=7,iface=MIXER,name='Auto Gain Control'
; type=BOOLEAN,access=rw------,values=1
: values=off
$ amixer -c 1 cset numid=6,iface=MIXER,name='Mic Capture Volume' 14
numid=6,iface=MIXER,name='Mic Capture Volume'
; type=INTEGER,access=rw---R--,values=1,min=0,max=16,step=0
: values=14
| dBminmax-min=0.00dB,max=23.81dB

again, store the settings so that they will be used again on a reboot:$ sudo alsactl store 1

Now we are ready to do a test recording, first check that arecord will see your card:

$ arecord -l
**** List of CAPTURE Hardware Devices ****
card 1: U0x41e0x30d3 [USB Device 0x41e:0x30d3], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0

and now for a ten second test recording, this will create a file called rectest.vav in your home directory. Remember to set the Device (-D plughw:1) number to the right card (card 1):

arecord -D plughw:1 --duration=10 -f cd -vv ~/rectest.wav the -vv option displays extra information on the screen as well as a volume meter, this should be peaking at around 95% on the loudest sounds, if it is at 100% all a lot of the time then you are probably recording distortion. Playback the recording with aplay:

aplay ~/rectest.wav

the default settings will play the wav fie through the TV if it is connected by HDMI, To playback through the USB sound card set the device to the card number, like in arecord:

aplay -D plughw:1 ~/rectest.wav

Congratulations, you now have a fully working Pi Recording Device. Remember to experiment with the volume levels, too high and your recording will sound distorted.

References:

  1.  Raspberry Pi Usb Audio fix (10 May 2013)

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.