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Lessons on how to use UltimaSerial
A very frequently requested application is to study the frequency domain of an analog signal. Although the serial devices from Dataq is too slow to analyze audio frequency (We do have an example on how to study frequency spectrum in real-time using UltimaSerial), I find their high-end products very useful. Unfortunately, they don't have a spectrogram add-in for their WinDaq software. So, based on the new features of their latest ActiveX control, a sample program WWB.VBP from their ActiveX package, and a shareware Spectrogram downloaded from the internet, I put together this fun project within an hour to show you how to view the frequency domain of an analog signal. You can even try to playback the converted sound file through your speaker!
With little modification, you can
easily convert this to fetch data from a serial device. If you do so, make sure you use
maximum sample rate of 240Hz, otherwise the Spectrogram will reject the file. We do have an example on how to display frequency spectrum in real-time
using UltimaSerial!
This VB program has the following limitations:
1) Only one channel can be extracted at a time
2) The sample rate is rounded to integer so that it can be opened by Spectrogram
3) The maximum sample rate per channel accepted is 50000Hz, while the minimum sample rate is 100Hz so that it won't be rejected by Spectrogram
4) The .WAV file size cannot be too big (to be determined), or the Spectrogram will not work
5) The maximum channel number in WinDaq file is 78 channels
6) When you try to play it back through your speaker, the sound card on your computer may not accept the sample rate of the file
To try this out, you need to:
1) Download the Dataq's latest data acquisition ActiveX control
2) Download the codes of my VB program.
3) Visit this page to get a better understanding of the WAV file format
4) Download the shareware Spectrogram
5) Generate a WinDaq file and name it sample.wdq, or download a sample here if you don't have one around.
6) Place it in the root directory of C:\ (if you use the default path of my sample)
7) Run Windaq Waveform Browser to take a look at the waveform
8) Run my VB program to extract a specified channel from c:\sample.wdq
9) Use the Spectrogram to open c:\sample.wav (if you use the default path of my sample)
When you are done with this, please go to my Home page to learn how to program Dataq's serial devices, including DI-194/190/150RS/151RS/195B, in VisualBASIC, Visual C++, LabView and Excel
Here are some screen shots:
The original WinDaq file opened under WWB.
The first channel is extracted from the above Sample.Wdq and convert it to .WAV file (Sample.wav)
Sample.Wav file is studied by the Spectrogram:
Last update: 10/05/07
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