Authors:
Marko Dimitrijević, Vančo Litovski - Faculty of Electronic Engineering, University of Niš, Serbia
Introduction
There are several approaches to the implementation of a computer-assisted laboratory for electronic education. In trying to keep the advantages of available concepts such as classical individual work, remote access laboratory, virtual laboratory and similar, this proposal is a mixed concept of a course laboratory for basic electronics at the introductory undergraduate level. A Computer Integrated Laboratory (CIL) allows for distance learning and virtual laboratory work while also keeping the physical experiment, substituting the majority of the instruments for virtual ones. The computer is used in practically in all phases of the work, starting from access and authorization, documentation, student-teacher interaction, simulation, virtual instrumentation synthesis, measurement control, distance learning and others. The results presented here are mostly related to virtual instrumentation
development and physical laboratory work.
Among the technologies that enabled the blooming of this educational subject is clearly the development of the Internet. It brought several new procedures, commonly referred to as e-learning, distance learning, remote learning, collaborative learning and other similar ones. The Internet not only allowed for easy and cheap access to knowledge and better, faster student-teacher interaction but also introduced the possibility for new concepts such as virtual laboratories based mainly on simulations. The term “Remote” is now limited only by the borders of the Internet. In addition, several software packages such as LabVIEWTM enabled the development of what is now called virtual instrumentation, which completely simplified the subject of instrumentation. Thanks to this kind of
software and accompanying hardware, practically every conceivable electronic instrument may be synthesized and made available to students at an incomparably low price.
A review of the solution
The goal of the laboratory work is to give students the possibility to experimentally verify theoretical lessons as they advance. The following exercises in basic electronics have been implemented:
Diodes
BJT–NPN and PNP transistors
JFET
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MOSFET
BJT Amplifier
MOSFET Amplifier
Multistage JFET amplifier
Operational amplifier
Colpitts oscillator
Audio frequency power amplifier
Rectifier and linear stabilizer
The layout of the laboratory is depicted in Figure 1.
Figure 1. Layout of the Laboratory
The virtual instruments used for exercises that include diodes and various types of transistors have the characteristic curve tracer VI, which when used for amplifiers are a type of scalar network analyzer. An
oscilloscope, frequency-meter and spectrum analyzer are also used to analyze specific electronic linear circuits.
Hardware implementation
The measuring unit, in our case, was implemented using the National Instruments USB-6251 acquisition module.
The module has 16 analogue inputs with 1.25MS/s sampling rate, two analogue outputs with 2.8MS/s sampling rate, 24 digital I/O channels and two 24-bit counters. USB-6251 is a USB-based acquisition module. External signals or devices under testing can be connected with an acquisition module using a block panel. The analogue outputs of the acquisition module are used as DC voltage generators for the power supply and stimulus voltage.
Maximal DC output voltage is limited to ±10V. This voltage is adequate for power supply, polarization and measurement of static characteristics of the semiconductor components. The measurement of voltages can be performed directly. Maximum input voltage is limited to ±10V. The measurement of currents can be performed only indirectly, by transforming current into voltage using a parallel resistor. In this implementation, a 100Ω, 1%
tolerance metal-film resistor was used, due to the increased precision of the measurement. Consequently, the value
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of 1mA is equivalent to 0.1V. The value calculation is performed as a software function. The sampling rate of analogue inputs/outputs is sufficient to analyze transistor amplifiers and filters.
Software implementation
Virtual instruments are implemented in National Instruments’ LabVIEWTM development package, which provides simple software creation and testing. Virtual instruments consist of an interface-to-acquisition card and an application with a graphical user interface. The user interface of the virtual instrument consists of visual controls and indicators. It provides basic functions for signal conditioning, measurement, and calculation of physical quantities. The user interface also provides controls for data manipulation and saving measured values.
Figure. 2. User Interface of Component Characteristic Tracer—MOSFET Characteristic
The interface-to-acquisition card is implemented as device driver. Modules are supported by NI-DAQmx drivers.
All the measurements are performed using virtual channels. A virtual channel is a collection of property settings that can include a name, a physical channel, input terminal connections, the type of measurement or generation and scaling information. A physical channel is a terminal or pin at which an analogue signal can be measured or generated. Virtual channels can be configured globally at the operating system level or by using an application interface in the program. Every physical channel on a device has a unique name.
The user interface (Figure 2) of the component characteristic tracer consists of visual controls and indicators. It provides basic functions for measurement. Visual controls—knobs and switches—provide control of analogue signal generation. The indicators—gauges and graphs—show the measured values. All measured values are placed in a table and, after the measurement process, in an appropriate file. The user interface also provides controls for data manipulation and saving measured values.
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Figure. 3. Main Thread of the Application
For better performance, the main application has been separated into two threads. The first thread has functions for file manipulation and saving measured values (Figure 3).
Conclusion
A computer-integrated laboratory for analogue electronics has an educational purpose. The main goal of this system is to simplify the manipulation of instruments, speed measurement and notate the results, providing students the opportunity to concentrate on acquiring measurements. It can be successfully implemented at a graduate-level basic electronics course.
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