Doug's MATLAB Video Tutorials

December 4th, 2007

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. This demo uses the Data Acquisition Toolbox.
Find the files here. PodCast here Other videos have been gathered here: http://blogs.mathworks.com/pick/category/video/ Other Advanced MATLAB posts have been gathered here: http://blogs.mathworks.com/pick/category/advanced-matlab/
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By Doug Hull

Doug first used MATLAB in 1994, could not figure it out until he got some help in 1995. He is now dedicated to making sure that no one else wastes a year of their life not knowing MATLAB like he did.

09:51 UTC | Posted in Format: PodCast, Format: Video, Level: Advanced | Permalink | 26 Comments »

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

  1. Juan Manuel Merlo replied on December 4th, 2007 at 19:45 UTC :

    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

  2. Doug replied on December 5th, 2007 at 11:12 UTC :

    Juan,

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

    http://www.mathworks.com/support

    Doug

  3. Di-An Hong replied on May 21st, 2008 at 12:19 UTC :

    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

  4. Doug replied on May 27th, 2008 at 12:21 UTC :

    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

  5. Dayal Strub replied on May 29th, 2008 at 08:31 UTC :

    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!

  6. Doug replied on May 29th, 2008 at 10:54 UTC :

    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

  7. Bob replied on May 29th, 2008 at 11:32 UTC :

    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

  8. Gert replied on June 13th, 2008 at 14:04 UTC :

    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

  9. Doug replied on June 13th, 2008 at 14:16 UTC :

    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

  10. Bryan replied on June 27th, 2008 at 09:57 UTC :

    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

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

    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

  12. Sherryl replied on August 28th, 2008 at 13:05 UTC :

    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

  13. Sherryl replied on August 28th, 2008 at 13:10 UTC :

    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

  14. pierre replied on August 28th, 2008 at 14:04 UTC :

    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

  15. Gamal replied on October 5th, 2008 at 11:17 UTC :

    Dear Sir,
    I am working in a project that i use an Analogue to digital converter HW to transfer analogue electrical data to digital. I want to read this digital these data via Matlab using USB port in order to get its FFT. I would be very glad if you tell me how to do that. thanks alot for your help.
    Gamal

  16. Doug replied on October 6th, 2008 at 08:19 UTC :

    Gamal,

    That is something that can be done. Do you have the Data Acquisition toolbox? What have you tried, can you connect to the board? What board is it?

    Doug

  17. Gamal replied on October 10th, 2008 at 14:12 UTC :

    Thank u Doug for ur fast reply. yes I have an NI-DAQ USB 6008. and I have an Analogue voltage sinusoidal signal that have a maximum frequency of 500KHz which means i want a minimum sampling of 1 Mhz. I want to analyze this signal using matlab( getting FFT) real time. can this be done by using the ADC in NI-DAQ or i have to get another ADC. if so how can i interface it with matlab. thanks alot Doug and I am waiting for your reply.
    Gamal

  18. Javier replied on July 6th, 2009 at 13:43 UTC :

    i’d like to know how can i import data for a transducer of human pulses into matlab without help of other hardware. the sensor has a USB terminal?

  19. Pirat replied on July 30th, 2009 at 12:30 UTC :

    hi doug. i want to ask you about using data acquisition card to record data from an oscilloscope realtime and process it with Matlab. i’m able to use getdata, but it’s blocking since i want real time recording and processing, then i will write a GUI to calculate the period, amplitude and some other things.Thank you

  20. dhull replied on July 30th, 2009 at 13:26 UTC :

    @pirat,

    You are best talking to htt://www.mathworks.com/support for this.

    Thanks,
    Doug

  21. Sal22 replied on February 6th, 2010 at 18:24 UTC :

    Greetings All

    I have a question on how I can prevent clicks/pause while trying to
    play a looped audio file (created in matlab) continuously.

    The working example below plays a 1 second 100hz signal 5 times but I
    can’t figure out a way to make it continuous so it doesn’t start and
    stop with that pause/click. I tried to increase the array to like 30
    seconds which would work but I want to run the loop for an hour or
    three. When I tried this I ran out of memory (the array was just to
    large to store in my 32bit 2gig ram windows system) Any suggestions/help

    I also would like to be able to change the frequency (nSigRepeat) using a slider in a GUI and have it update / play the audio in realtime are their any video tutorials on this

    
clear;
fs=44100;
nSigRepeat=100; %how many times signal repeats in a second
nTimeIncreaseTo=1; %Duration of signal in seconds
x=linspace(0,nTimeIncreaseTo,fs);
y=sin(2*pi*x*nSigRepeat)*.8; %adjust amplitude by multiplying to
prevent clipping

xi=linspace(0,nTimeIncreaseTo,fs*nTimeIncreaseTo);
xi=xi';
yinterp=interp1(x,y,xi,'linear');
wavwrite(yinterp,fs,16,'c:\delHz.wav');

subplot(2,1,1)
plot(yinterp);
subplot(2,1,2)
plot(x,y);

%Plays audio file for 1 second 5 times at 100 hz.
for i=1:5
    soundsc(y,fs);
end;

    tia sal22
    and keep up the great work

  22. dhull replied on February 8th, 2010 at 17:19 UTC :

    @sal22

    http://www.mathworks.com/access/helpdesk/help/techdoc/ref/audioplayer.html

    I think that you might be able to get audioplayer to do what you want. I wonder if the click you are getting is because of a discontinuity between the end and beginning of the loop.

    If you have Data Acquisition Toolbox, then you might be able to create and analog output and push data out that way and avoid the discontinuity problem also.

    What kind of audio data are you attempting this with?

    Doug

  23. Guillaume Defrance replied on March 15th, 2010 at 14:42 UTC :

    Hi Doug,

    I have a question about how to use a National Instruments PCI 6120 card with Matlab. The sampling frequency can go up to 1MHz, as far as I undesrtand from the specifications. However, with MatLab, I can’t set it greater than 500kHz.

    set(ai,'SampleRate', Fe); % this is my input line
% Here is the Matlab answer
??? Error using ==> daqdevice/set
Unable to set SampleRate above maximum value of 500000.

    Do you or anybody have heard about this problem? I am pretty sure there exists a way to force the NI card to a larger sampling frequency when it is given in the specifications of the card, maybe by changing some properties of the card using Matlab?
    Thank you in advance for your answer.

    – Guillaume

  24. Amin replied on April 2nd, 2010 at 20:34 UTC :

    Hi,
    i m working on a project, i must control my PCI Data Acquisition Card (Keithley KPCI-3103A) and make it send (with matlab commands) Pulses through a Digital Output to a Sensor board.
    These Signals must be at least 13µs High and 13µs Low (with adjustable pulses Number, Duration and Pulse Width) i looked maybe the whole Documentation about DAQ Toolbox and another Privat things, but nothing of that helped me. I m really confused.
    I can get the Analog signal from the Sensor Board (Adaptor is already registred) but when it´s not controlled with the mentioned signal it is just a normal Input Signal.

    I hope somebody can help

  25. dhull replied on April 2nd, 2010 at 20:36 UTC :

    @Amin,

    The best place for this kind of question is:

    http://www.mathworks.com/support

  26. Navin Kumar replied on May 3rd, 2012 at 21:07 UTC :

    Hi Doug, I am doing my final year project in which I need your help. My project is based on real time system(Level sensor). I have to control the level of the water in the tank using microcontroller and MATLAB. Till now I have already done the microcontroller part but, I am stuck with MATLAB GUI. I need your help to show the data in MATLAB GUI while the test is running. I have used ATMega32 microcontroller and ZigBee Transceiver Module.
    Thanks.

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