OWON Digital Oscilloscope
1. Battery Pack Hack
2. Spectrum Analyser Hack (download this Python Program from the files listed at the end of this page)
Python Download
I have recently obtained an OWON digital oscilloscope (PDS5022S) from CPC in the UK (approx £225 2009). Several very similar versions are available, all very competitively priced.
These Chinese oscilloscopes are definitely not as well built as the more expensive laboratory grade ones from Agilent, Tektronix and the others but they do still represent good value for money for most general purpose applications. They are excellent for schools, hobbyists and for general purpose work. However if you were using one all day you might prefer a brighter CRT screen.
1. BATTERY PACK HACK
As this probably invalidates your warranty it is totally at your own risk!
The first improvement concerns the addition of a battery pack in order to make the oscilloscope a little more portable. The standard product offers a battery pack as a very expensive option (£60). Clearly this can be improved. In my case I don't actually need hours of use, just a few minutes would normally be enough to get some provisional readings to justify either bringing jobs into the workshop or running an extension lead or rigging up a remote supply. Therefore a number of rechargeable NiMH cells would probably do the trick.
A visit to POUNDLAND (where everything costs £1) soon obtained a total of 6 rechargeable AA cells for a total cost of £3.
Opening the battery compartment on the rear of the oscilloscope showed that there was easily enough room for these six cells. Measuring the voltage across the charging points when mains powered, showed 8.4v. Thus 6 cells giving 7.2 v would allow them to be charged without further modification. Note that the polarity is NOT the way you would expect! The RED wire is the POSITIVE one.
The batteries were connected together in series with some insulated wire. The battery pack was reinforced using some double sided tape and a couple of pieces of cardboard. Two more pieces of card prevent the batteries from sliding around the inside of the compartment. I soldered the wires directly to the battery tags.
OK, so its not brilliant and the batteries only last half an hour but at 1/20 the price I don't care!
Note that in order to charge them up, you ned to turn on the oscilloscope and select the correct menu items.

2. SPECTRUM ANALYSER
One of the really great things about a digital osciloscope is that the waveform can be exported to a computer. It can this be saved, printed, e-mailed or even subjected to further analysis. The OWON scope comes with a Windows driver and some very basic software. This software is mostly written using JAVA but unfortunately it's not possible to easily write your own code without doing a little reverse engineering. If you want to analyse the data from the oscilloscope in Windows you basically have to use the OWON applicaton to grab the data and then export the data file in text format to be analysed by another application such as Excel. This is alright if you only need to analyse a few waveforms but is a real nuisance if you want to analyse lots of data. Not only that but it is also a bit difficult to automate certain operations such as implementing a SPECTRUM ANALYZER
As usual I wanted a LINUX implementation because it would be much easier to write a short script to evaluate data on my LINUX machine. Initially I had intended to start reverse-engineering the oscilloscope myself but then discovered that this had already been done. The application called 'Owondump' is written by Michael Murphy.
You can download the latest source code from here.
Although these files are provided as source code, it is really easy to compile and the instructions are excellent. On my laptop PC it compiled in just a few seconds!
On my machine all I had to do was follow the instructions:
1. Download the owondump-0.2.tar.gz. Then extract the files to a suitable working directory.
2. You also need to download and install
gnuplot (using synaptic package manager)
gcc (almost certainly already on your PC)
GNU make (almost certainly already on your PC)
libusb-0.1-4 - http://libusb.wiki.sourceforge.net/
and
libusb-0.1-4 dev
If they are not already installed.
Actually you only need GnuPlot if you intend to use it to plot the captured data.
3. Compile everything yourself using gcc. Just open a terminal window and navigate to the directory where you extracted the files. At the command line type the folowing (some machines may require you to do this as root).
gcc -lusb -o owondump owondump.c
and
gcc -lusb -o owonfileread owonfileread.c
This creates two executable files called owondump and owonfileread.
To run the capture from the scope you need to be root
# ./owonscope
Note that the dot-slash tells Linux to run the program from its current location.
As usual there are a few Gotchs. You have to remember to connect your oscilloscope using the usb cable. And remember to turn it on... And one last point; you must set your oscilloscope to export vectors not bitmaps. It worked first time for me (Mepis 8 -a Debian Lenny based distro running on some quite old hardware).
The above command should create a data file in your default directory called output.bin.txt. This file will contain the plain text raw data captured from the oscilloscope. You can either open it with a spreadsheet or process it further using other tools.
Of course its a bit of a problem opening a terminal and switching to root every time you want to run the owondump capture utility. The solution is to use visudo to and the owondump application to the list your user can use without a password. There are a few other useful tricks you can do as well. Read on for more....
PYTHON-GNUPLOT-SPECTRUM-ANALYSER
You can easily automate the process of data capture and analysis using a simple PYTHON script (right click, save as...) program.
In order to use this your system must have the folowing components installed
1. Python (I use version 2.5.2)
2. Python-Numpy
3. Python-Gnuplot
4. GnuPlot (so you can do the job manually as well if needed)
You could just open a terminal and type 'python fft_spectrum.py' and hit enter. Again, I'm lazy and like to just click on an on-screen icon. In order for this to work you will need to add the owondump application to the list of allowed applications for sudo.
Here is a rough set of instructions. You may need to modify paths for your own machine.
PREPARATION:
Copy all the following files to a suitable directory. The following examples use the path
/home/chris/Documents/owon-app/ . If you use a different path you will need to use it throughout. Also note that the python script is set up to use this path as well so you may need to change it slightly for your own machine.
There are three places in the python program where you need to insert your own path instead of my default one. You need at least the following in the correct folder mentioned above.
1. owondump (Right click and check the properties of this program to ensure it is executable otherwise you won't be able to run it)
2. fft_spectrum.py
This is the PYTHON application which does the processing.
PRE-REQUISITES:
You must have :
PYTHON installed on your machine. Most distros have this installed by default.
You will also need
GNUPLOT
PYTHON-GNUPLOT
PYTHON-NUMPY
You can normally obtain these via your distibution's package manager.
ENABLE A NORMAL USER TO RUN OWONDUMP:
To enable a user to run the owon dump application without a password
As ROOT run the VISUDO command. Open a terminal and switch to ROOT (su or sudo) to do this.
Add an entry as follows
%users ALL=NOPASSWD:/home/chris/Documents/owon-app/owondump
This will enable users to run a shell script which can call owondump without the need to enter a password each time. (Using your own path of course!) Since owondump is in a directory owned by chris, other users would not actually be able to run the owondump application because normally they would not have permission to access chris' home folders. Don't be tempted to simply allow users to run all commands without passwords as this severely compromises your system security.
DESKTOP ICON:
Create a Desktop quick launch icon (Using KDE 3.5)
Right click on the Desktop
Create New -> Link to Application
In the GENERAL TAB:
Then enter a suitable name such as OWON-GRAB
Click on the default icon to change it to something more interesting
In the APPLICATION TAB:
Command: python fft_spectrum.py
Work Path:/home/chris/Documents/owon-app/
(Use your own path as it is very probably different)
ADVANCED OPTIONS: Tick Run In Terminal
And select apply/ok as needed.
Provided you have allowed users to run 'owondump' you can just click on the new icon to grab and analyse data from the oscillocope.
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And here is what you get if you measure the calibration square wave using the standard probe.
Original Data
FFT Spectrum