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The virtual Instrument based on labVIEW and Sound Card


Card ZHAO Xian-ling College of Electronic Information Engineering Taiyuan University of Science and Technology Taiyuan China hdhchx163.com Abstract—Sound card is a multi-channel digital and a

nalog signal conversion system each other. It can replace data acquisition card in some virtual instruments. A virtual oscilloscope and function waveform generator have been designed to use labVIEW and sound card. The oscilloscope can accurately display the external signals acquisitioned by sound card. The function waveform generator can produce sine waveform square waveform triangle waveform saw tooth waveform Gaussian white noise waveform tones and sine waveform and formula waveform. The amplitude of these signals are within 1V and the frequency of these signals are within the scope of 20Hz to 20kHz. It proves virtual instrument based on sound card that can be applied to data acquisition and control applications. Keywords- virtual instrument labVIEW sound cardoscilloscope function waveform generator I. INTRODUCTION The I/O interfaces of virtual instruments are mainly five kinds: PC-DAQ/PCI card GPIB bus VXI bus and Serial bus and PXI bus. PC-DAQ/PCI card is the most basic and cheapest composition of VI 1. Generally LabVIEW only supports the data acquisition card of the national instrument while the prices of these cards are relatively expensive. In order to be able to drive common data in

LabVIEW the user must call Library Function Nodes and the Code Interface Node to write the corresponding driver of the acquisition card. Sound card is a dual channel A / D and D / A signal acquisition and output devices. As the sound of high-volume production the price much lower than similar in terms of A / D or D / A card usually a few ten-fold difference. Sound Card is designed with PCI and it can better communicate with CPU. LabVIEW has a strong signal processing capabilities including image and sound. The functions of sound processing are in the Functions PaletteGraphicsSoundSound. This series of functions are written with the windows low-level functions. As the windows low-level functions are to deal directly with the sound card driver they speed fast and package a low-level. They can access acquisition data from anywhere in the buffer. They have a lot of flexibility to meet the needs of real-time continuous acquisition. II. THE I/O INTERFANCES OF SOUND CARD Generally sound card has 4-5 external interfaces. There are two input interfaces namely Mic In and Line In. Mic In receives weaker signal amplitude for the 0.02-0.2V Line In receives not more than 1.5V signals. These two interfaces can be used for the oscilloscope input interfaces. There are two output interfaces namely Wave Out and SPK Out. The output signal from the Wave Out without amplification requires an external power amplifier. The output

signal from SPK Out is amplified and it can be directly received by the speaker. These two interfaces can be used as a dual-channel signal generator outputs. Musical Instrument Digital Interface MIDI can record and playback a variety of realist ic acoustic instruments of music. III. THE REALIZATION AND PERFORMANCE INDICATORS OF THE VIRTUAL OSCILLOSCOPE A. The realization of the virtual oscilloscope In the LabVIEW data acquisition objects the sound signals are special. After the sound signals are converted to the analog electrical signals by the sensor they are acquisitioned by the sound card. After that the analog signals are converted into digital signals into the user program. In this case the sound card will completely replace the data acquisition card DAQ to acquisition the analog signal. As shown in Figure 1 we can use sound card to acquisition electrical signals. There are several functions about sound processing such as Sound Input Configure. VI and the Sound Input read. VI in LabVIEW. Using the functions and the sound card I designed a virtual oscilloscope. In this paper all procedures were programmed with LabVIEW8.20. Figure 1. Sound signals into the user program. Figure 2 is the front panel virtual oscilloscope which shows in detail waveform the average phase cycle peak-peak

instantaneous

amplitude

RMS

amplitude-frequency

characteristic and phase-frequency the signal characteristic of the

sine. Sine waveform was generated by Good WillGFG-8250A Function Generatorfrequency range 1HZ - 1M Hz. sensor sound card audio signals electrical signals digital signals user program 2010 International Conference on Computational Aspects of Social Networks978-0-7695-4202-7/10 26.00 ?? 2010 IEEEDOI

10.1109/CASoN.2010.170743Figure 3 is the block diagram of the VI which includes sound input configure .VI sound input read. VI FFT.VI and Amplitude and Level Measurements.VI. The function of Amplitude Measurements. VI. can calculate a complete cycle of the signal the average level and the signal level of positive and negative peak and peak-peak. Figure 2. the sine waveform acquisition and analysis in the system Figure 3. the diagram of sound acquisition and analysis in the system There are pre-amplifier in Mic In. It can introduce noise to cause signal overload. When the signal is imported into the users program through Line In the interference is small. Therefore choose Line In to import signal 2. On the front panel we set the device ID number is 0. Connect the Line In to the signal generator. Set system parameters in the Sound Input Configure .VI as below: buffer length is 8KB sampling frequency is 22.05 kHz. From the computer screen we may observe the sine waveform. The oscilloscope successfully displayed the signal from the Good Will GFG-8250A Function Generator. In order to protect

the sound card we should fully estimate the amplitude of the measured signals. If they are large they can not directly enter the sound card. They must be limited in the range of 1V. B. The performance indicators of the virtual oscilloscope Sound card can achieve dual channel 16-bit or 32-bit high-precision data acquisition. The sampling frequency can be 44.1 kHz 22.05 kHz 11.025 kHz 8 kHz. Each channel sampling frequency can be up to 44.1 kHz. The sampling depth is up to 24 bit. It can be almost perfect to measure any sound signals within the scope for example: vibration speed heart and lung auscultation electrocardiogram seismic waves sound power harmonics and so on. Simultaneously acquisition mult i-channel signal you can choose to configure high-end sound card or multi-block sound card 3. Now there are 8 channel sound cards on the market and its maximum sampling frequency is 48 kHz. The performance of the sound card is better. IV. THE REALIZATION AND PERFORMANCE INDICATORS OF THE VIRTUAL FUNCTION

GENERATOR Sound card also has D / A functions. There are several sound processing functions such as Sound Output Configure.VI Sound Output Write.VI Sound Output Clear.VI in LabVIEW. We can use these functions and the sound card to complete a function waveform generator. A. The realization of the virtual function generator After the digital data are converted into analog data by

sound card they are transited into the devices such as the speaker box etc. To use the sound card D / A functions we can design a virtual generator. Sound output configure.vi Sound Output Write.vi Sound Output Clear.vi coupled with the necessary functions and controls can be completed function generator design. Figure 4 is a virtual front panel of the virtual signal generator waveform chart control for real-time display of the output waveform. Figure 4. the panel of the function waveform generator Figure 5. the diagram of the function waveform generator 744Figure 5 is the diagram of the signal generator. It mainly consists of while loop case structure Sound Output Configure.VI Sound Output Write.VI and Sound Output Clear.VI. While loop is a device switches. Case structure is used to select the type of signal. There are a variety of signal types including the formula nodes in the signal processing functions. There are sine waveform square waveform triangle waveform saw tooth waveform Gaussian white noise waveform tones and sine waveform and formula waveform in this program. Each of the signals has been programmed into subroutine. In these subroutines we may set the parameters such as amplitude frequency phase and so on. The amplitude and frequency can be arbitrarily set in the subroutines. In fact the output signal amplitude and frequency is restricted. Sound Output Configure.VI is used to set the parameters

of sound card such as sample rate data format the buffer length. Sound Output Write.VI is used to wait for the full message of data buffer. When the message is generated CPU writes the contents of the data buffer to the user program array. Sound Input Clear. VI completes the final clean-up. For example it turns off the sound card sampling channel and releases of a series of system resources including the MDA the buffer memory the I/O interfaces of sound card etc. Firstly connect the Wave Out of sound card and the oscilloscope CA1022/CA1052 with wires. Secondly set the signal sampling frequency and buffer size in the Sound Input Configure.VI. Thirdly select the type of output signal. Finally run the program. Adjusting the oscilloscope the waveform generated by the virtual signal generator is shown on the screen of the oscilloscope. B. The performance of the virtual function generator If the maximum sampling frequency of the sound card is 44.1 kHz according to sampling theory the frequency of maximum analog signal is 22.05 kHz. Systematic sampling accuracy is related to the sound card bits. If we choose 16-bit sound card the sampling accuracy is 1 / 216 0.000015 the resolution is about 0.0015.The maximum bandwidth of sound card can be up to 133 kHz. V. CONCLUSION Sound card is a professional data acquisition system. It has stable performance and low price. A virtual oscilloscope and signal

generator are designed using sound card and labVIEW. The instruments based on sound card and LabVIEW open up a new design method of VI. It proves that the VI based on sound card can be applied to common data acquisition and control applications. They are convenient flexible and inexpensive for some applications is a good choice. On the market the high-performance sound cards appear continuously. The sound card connected to USB is next generation trend. The virtual instrument based on sound card will be widespread. REFERENCES 1 Liu JH Jia HQ. Virtual Instruments LabVIEW graphical programming language tutorialM. XIDIAN University Press. 2003.05. p102 2 Qu XQLiu Z. Audio signal acquisition and analysis system design based on sound cardJ Electronic TestTest Tool s Solution.200902:75-77 3 Chen DF Wu GH. A virtual oscilloscope based on sound cardJ. Micro Computer Information Control Automation. 2008249:189-190. 745


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