Advanced MATLAB: Data acquisition in MATLAB

MATLAB is often used for post-test data analysis. You can get more value from your data acquisition session if you do the MATLAB analysis on the data as it is being collected. This can be done by having MATLAB be the software for collecting your data.

This video shows a very simple way of getting data into MATLAB from a DAQ board, in this case the windows soundcard.

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14 Responses to “Advanced MATLAB: Data acquisition in MATLAB”

Juan Manuel Merlo replied on December 4th, 2007 at 7:45 pm :

Hi Doug, I saw your demonstrations of http://blogs.mathworks.com/pick/2007/12/04/advanced-matlab-data-acquisition-in-matlab/, but I can’t see the winsound input, matlab said me the following:
??? Error using ==> analoginput.analoginput
Error using ==> analoginput.analoginput>localCreateAnalogInputObject
Failure to find requested data acquisition device: adaptor.
Can you help me please?
Thanks
Juan Manuel “El Mer” Merlo

Doug replied on December 5th, 2007 at 11:12 am :

Juan,

This is a question best answered by my colleagues in Technical support. They can be reached here:

http://www.mathworks.com/support

Doug

Di-An Hong replied on May 21st, 2008 at 12:19 pm :

My questions are
How to use Matlab to record computer mouse movement
Do I need the Data Acquistion Toolbox to do so

Thanks,
Di-An

Doug replied on May 27th, 2008 at 12:21 pm :

Di-An

I just put up this video:

http://blogs.mathworks.com/pick/2008/05/27/advanced-matlab-capture-mouse-movement/

This should help you.

Doug

Dayal Strub replied on May 29th, 2008 at 8:31 am :

Hi Doug, I have a question regarding DAT and usb mice, which doesn’t fit under either of your two previous posts.

I am trying to devise a cheap pendula experiment for university and highschool students,
the idea is to use a usb mouse (as has been done before, but differently and not using Matlab) as the sensor. I would like to use Matlab to acquire data from the usb mouse (specificaly the coordinates which would now be angles), but it should not be identified as a mouse, and should not interfere with the computers primary one.
I thought it might be possible to use DAT by creating an adaptor for the usb port, and then considering considering it as a digital input and not as a mouse.

As I have never used DAT before I am not sure this is possible, and if it is, exactly how to go about it.
Any help would therefore be very much apreciated!

Thanks!

Doug replied on May 29th, 2008 at 10:54 am :

Dayal,

USB is not a protocol but if you have a dll driver for the mouse and know the API you can write a DAT adaptor.

Having said that, writing a DAT adaptor is not an easy task and we usually recommend it only for the hardware vendors themselves. This doc

http://www.mathworks.com/access/helpdesk/help/pdf_doc/daq/adaptorkit.pdf

has all the information necessary for writing an adaptor.

There are some inexpensive USB devices available that we do support (some from Measurement Computing, some from National Instruments) but you would then need to find a sensor.

DAT does not appear to be the correct solution for this problem.

Doug

Bob replied on May 29th, 2008 at 11:32 am :

Dayal, here’s another thought that could use the Data Acquisition Toolbox. Use a rotary potentiometer (variable resistor) as a sensor. The basic idea here is voltage divider. Place a reference voltage (say 5V) across the ends and connect the wiper pin to the analog input channel. The digitized voltage would be proportional to the rotation angle of the pot. Many cars now use exactly this for the gas pedal sensor, In fact, maybe you can take the foot pedal off a video game, or from a sewing machine, etc.

Cheers
Bob

Gert replied on June 13th, 2008 at 2:04 pm :

Hi Doug,
Is there a way to analyze the rpm of an engine from the sound with Matlab? I downloaded an example “Real time octave analysis” http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=3076 and I tried to put in a band-pass filter but the program crashes every time when I try to run it.
If there is a way to do that, can you give me an idea how? For an 12 cylinder 4stroke engine and rpm between 800 – 9000 (16.67-150 Hz) it gives a maximum of 900 pulses a second. So I think I will need than a Fs > 1800 Hz. But is there a way to filter real time data ?

Thanks,
Gert

Doug replied on June 13th, 2008 at 2:16 pm :

Gert,

I can not speak to the stability of any of the File Exchange, you will need to speak to the original author about that. However, to filter “Real Time Data”, you need to be more specific. Are you tying to get the results of your analysis while the test is running, or is this post test analysis. If you want the results while the test is running, how “Real Time” do you need to be. You might end up using Real Time Workshop. Explain more what you are looking for, and I will try to help.

Doug

Bryan replied on June 27th, 2008 at 9:57 am :

Hi Doug -

I’m trying to use an accelerometer to measure the tilt angle and record that data in MATLAB. I have it hooked up to a power supply and to a Measurement Computer USB-1208FS DAQ. Then I have code in MATLAB to acquire the data. It works for a second or two, but then it stops. Is there a template code for doing something like this? Any clue on the problem?

- Bryan

pierre replied on August 28th, 2008 at 11:47 am :

Hi all,
I have the Data Acquisition Toolbox, and I’m trying for 2 weeks to send a step voltage, and just after another one of a different voltage WITHOUT going back to “zero” between the two..
I tried to do it little by little and I saw that the “start” function between the two steps reinitialize the voltage at a value of zero volts. And I wouldn’t like it because the piezo I want to control has a really fast response time..

Furthermore I think I am compelled to use a “start” function between the two steps because I have to compute de Amplitude of the second step in real time so I don’t have to prepare the two steps before and put both of them in the engine using one “putdata”.

Is there a way to avoid it ?
Thank you a lot, This problem is really annoying me.

Pierre

Sherryl replied on August 28th, 2008 at 1:05 pm :

Hello Pierre,

Please look at the OutOfDataMode property.
http://www.mathworks.com/access/helpdesk/help/toolbox/daq/outofdatamode.html
You can use it to set a value that will be held when the queued data has been output.

start will not set the output voltage to zero until that value is in your output signal.

Regards,
Sherryl

Sherryl replied on August 28th, 2008 at 1:10 pm :

In Response to Post #10 by Bryan -
Hi Bryan,
By default the analog input object will acquire one second worth of data.
There are many ways to acquire more than that.
1. Set TriggerRepeat to greater than 0
2. Set SamplesPerTrigger to a larger number than the default, which matches the default SampleRate
3. Use either a TimerFcn or SamplesAcquiredFcn callback to restart the acquisition

All of these things are well documented here:
http://www.mathworks.com/access/helpdesk/help/toolbox/daq/daq.html
They can also be seen in the demos . Bring up MATLAB and type:
demo(’toolbox’,'data acquisition’)
at the command line (requires that Data Acquisition Toolbox already is installed).

Regards,
Sherryl

pierre replied on August 28th, 2008 at 2:04 pm :

Hi sherryl and thank you for answering me,

Actually, I already tried before to use this property because I saw that it was what I wanted, nevertheless I got this error:

EDU>> AO = analogoutput(’ueidaq’,'pwrdaq://dev0′);
EDU>> addchannel (AO, 0);
EDU>> AO.OutOfDataMode = ‘DefaultValue’;
??? Error using ==> daqdevice.subsasgn at 108
Error using ==> daqdevice.set at 261
Invalid property: ‘OutOfDataMode’.

Then I tried to skip it just by doing :
EDU>> AO.Channel.DefaultChannelValue = 5;

And then I had no error but also no effect : I still got a value of “zero” instead of 5 volts between the two steps ..

I don’t know why this property is not recongnized, do you ?
I am using the R2007a student version of matlab.

Thanks,
pierre

About

Doug Hull is an Application Engineer at The MathWorks. A MATLAB user since 1994, he gets paid to live, eat, and breathe MATLAB! This blog is dedicated to promoting the File Exchange by highlighting files and original video content.

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