Application of virtual instrument LabVIEW in digital circuit experimental teaching

1 Introduction

The so-called virtual instrument is a computer instrument system that is based on a hardware platform with a computer as the core, equipped with corresponding input/output interfaces, a virtual panel of a computer display, and the test function is implemented by test software [1-2]. Since the National Instruments (NI) of the United States proposed the concept of virtual instrument in 1986, virtual instrument technology has become a research hotspot and application frontier in the field of automatic measurement and control in developed countries. At present, the most famous virtual instrument system is NI's LabVIEW, and its most widely used application field is the field of measurement and control [3-4]. This article will discuss the application of this system to the teaching and experiment of digital logic circuits. This article believes that due to the characteristics of virtual instruments and the differences between digital and analog circuits, virtual instrument systems are not suitable for the teaching or experiment of analog circuit systems, but have strong and special advantages for digital circuit systems.

2. Problem Solving

The virtual instrument LabVIEW has a typical graphical language style. The process of compiling its program (rear panel) is the process of selecting, combining and connecting different icons (VIs). Its different icons (VIs) are equivalent to "subroutines" with different functions. The connection between icons specifies the flow of data, which is equivalent to the "assignment" statement of the code language [5]. The function palette of LabVIEW contains a large number of special VI icons such as signal processing and signal operation, as well as basic VI icons for various numerical operations and logical operations. The icon of the logical operation VI is the standard logical operation symbol. The corresponding logical operation VI palette in LabVIEW is shown in Figure 1.

It is not difficult to see that the logic operation program (LabVIEW back panel) compiled using these icons is a standard logic diagram of a digital logic circuit. As for signal input/output, LabVIEW also provides a wealth of input controls and output controls, such as various forms of switches, buttons, indicator lights, waveform displays, etc. These "devices" can be directly dragged and dropped to the corresponding position for use.

Figure 1. Boolean VI palette in LabVIEW

More importantly, the virtual instrument system is different from virtual reality technology or simulation technology. The latter two are just a simulation of the real system. Although the virtual instrument is called "virtual", its essence is a real instrument system based on computer software and hardware systems as support, which completes the processing process by adopting certain mathematical models and algorithms. In a word, the virtual instrument system is not a "virtual" instrument, but a "real" instrument, which is to complete the functions of the real instrument system. In other words, the corresponding experiments or teaching processes based on the virtual instrument system, by configuring the relevant A/D or DAQ interface, become instruments that can complete the functions of actual instruments. Therefore, teaching and experiments based on virtual instruments are more practical than teaching experiments based on virtual reality technology or simulation technology!

Since the Boolean operation VI provided by the virtual instrument LabVIEW is relatively complete, coupled with the graphical language style of the system itself, it is completely possible to combine the processes of "program-logic diagram-experimental process-input and output", making the process simple and clear, and can complete almost all experiments and demonstrations in digital logic circuits, such as: encoders, decoders, data selectors/distributors, adders, various counters, etc. Moreover, for specific experiments or demonstrations, the "high-brightness single-step execution" mode of the program execution process in LabVIEW can be used to fully observe the dynamic flow of signals and the operation process of logic circuits. Even a certain logic operation process can be developed separately as a special user VI, forming a new concept of "virtual chip" with unique functions for direct call when needed. The following takes a simple seven-segment digital display decoder as an example to discuss the process of using the virtual instrument LabVIEW to realize digital circuit experiments.

3 Design of digital circuit teaching experiment

Digital displays are commonly used display devices, and seven-segment display decoder logic is a typical design example commonly used in digital logic circuit teaching. The following takes the design of a seven-segment display decoder as an example to illustrate the application of the virtual instrument LabVIEW in digital logic circuits.

3.1 Design requirements

The required digital display font is shown in Figure 2. Assume that the input I3 I2 I1 I0 is a four-bit binary number, ag is the corresponding seven-segment display output, and its logical relationship is equation group 1.

Figure 2 Seven-segment digital display font

3.2 Design process and experiments[page]

The program is constructed using the virtual instrument LabVIEW, and the rear panel constructed according to equation group 1 is shown in FIG3 .

Figure 3 LabVIEW back panel of the seven-segment display decoder (program)

As can be seen from Figure 3, the LabVIEW back panel (program) and the corresponding logic circuit are completely corresponding in form, that is, the LabVIEW program is actually the concrete embodiment of the logic diagram. If the "high-brightness single-step execution" method is used, the flow of information (signals) and the intermediate calculation results of each link can be observed intuitively, which is beyond the reach of other digital logic experiments. This is also the intuitiveness, simplicity and practicality of digital logic experiments based on the virtual instrument LabVIEW.

The corresponding program front panel (output/operation interface) is shown in Figure 4.

Figure 4. The front panel of the seven-segment display decoder experiment

In the experiment, four switches I0~I3 are used as logic devices for generating four-bit codes, and seven indicator lights a~g are used as display units of the seven-segment digital display. These "devices" are ready-made input/output controls provided by LabVIEW and can be used directly.

What is currently shown in the figure is the decoded display "9" when the input is "1001". During experiments or demonstrations, you only need to use the mouse to operate the horizontal rocker switches I0~I3 to obtain the relevant input codes, and the corresponding output (decoding display) will be displayed on the right. Of course, you can also use the "CTRL+E" key combination to call up the program back panel window Figure 3, and use the single-step high-brightness execution method to observe the working process of the decoder.

4 Advantages of virtual instruments in digital circuit experimental teaching

Introducing virtual instruments for experiments and teaching, in addition to the above-mentioned characteristics of easy implementation, simple process and obvious effect, can also achieve the following goals:

Low cost of advanced instruments
Shorten the development cycle of new instruments
Reduce the maintenance and configuration costs of instruments
Easily implement interactive experiments and teaching based on the network
Strengthen the autonomy and creativity of learning and experimental processes

Achieving the above goals can improve the corresponding teaching model, create very favorable conditions for cultivating innovative talents adapting to the new century, and provide an ideal development space for improving the strength of colleges and universities and reducing teaching costs. It can be predicted that virtual instrument technology will be an important direction for the development of instrument science for a considerable period of time in the future [6-7].

5 Conclusion

The application of virtual instrument systems in experiments or teaching is another application field of virtual instrument systems besides the testing field. The application of virtual instrument systems in experimental teaching of digital logic circuits can give full play to the advantages of virtual instrument systems, make the teaching process more intuitive, enable the experimental process to fully reflect the participation of students, and strengthen the design and practice of self-created experiments. Moreover, virtual instruments have a wide range of applications in digital logic circuit experiments. With the addition of appropriate A/D or DAQ, such systems can be easily upgraded to practical virtual instrument-based experimental/analysis systems.

The application of virtual instruments in the teaching and experiments of digital logic circuits has great practical significance and is also another important supplement to the application of virtual instruments outside the testing field.