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This section presents the Java [8] software application
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which controls and monitors the OpenLab Signal Generator.
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Furthermore, the features and functions of this measurement
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tool, as well as the benefits for students, are discussed. The
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main window of the signal generator with its arbitrary signal
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generation function is illustrated in figure 11.
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The application is able to output standard waveforms such
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as sinusoidal, rectangular, saw tooth shaped, and triangular
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signals. Furthermore, students are able to generate arbitrary
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waveforms using the built in tool. This feature is especially
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useful during courses dedicated to audio signal processing
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and analog/digital signal processing. The signal generator
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supports two different methods in order to output arbitrary
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signals. The ”Definition Through Points and Interpolation”
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method enables the user to define a signal graphically by
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placing key-points on the graph. After pressing the ”Generate
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Waveform” Button, the software calculates the missing steps
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between the key-points, using interpolation, and displays the
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final waveform. This approach is best suited for beginner
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students, due to the easy-to-understand procedure. The
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”Definition in Frequency Domain” method requires the user
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to specify the sine components that should occur in the output
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signal. Through the main menu of the user application, the
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user can open the input mask for the frequency components.
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In order to ensure correctness of the user input, the data is
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validated by the application. Students are able to choose the
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FFT Bin, the magnitude, and the angle of the harmonics.
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Based on the user input a wavetable with dedicated FFT
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Bins is stored and an Fast Fourier Transformation (iFFT) is
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performed on this set of values. For the iFFT the Cooley-
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Tukey algorithm [15] is used within the application. After the
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iFFT, the real components are extracted from the complex
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output and are scaled to the range of 1, in order to fit the
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allowed ranged of the wavetable values. The calculated data
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is displayed within the preview window of the application
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and can be applied to one of the signal generator outputs.
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This signal generator provides two channels which can be
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controlled separately. Students are able to vary the output
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frequency for each channel using the corresponding knob in
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the Frequency section. The same applies for adjusting the
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required signal amplitude and for adding any desired offset
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value.
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In order to enable further development of the OpenLab
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Signal Generator, the user application is designed to support
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additional signal generator hardware. This means that the
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output logic is encapsulated and can be handled in a generic
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way. Each signal generator solution has to inherit from a
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specific class and implement all the functions to be compatible
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with the user application. It can be seen as a high level device
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driver that communicates with the device. As a result, students
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are able to design and built their own hardware, which can be
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added to the Java software using a common interface. In the
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current state of development, the OpenLab Signal Generator
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supports generic PC soundcard devices as signal source. To
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ensure platform independence, the Java software utilizes the
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open-source PortAudio [16] library. Even without the external
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signal processing hardware, described in V, students are able
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to perform basic measurement tasks. Therefore, in order to
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demonstrate signal characteristics, only a PC running the
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OpenLab software is required. |
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