A zero-cost, real-time, Windows signal laboratory

International Journal of Electrical Engineering Education, Jan 2009 by Leis, John, Snook, Chris

Abstract This paper introduces a Windows-based signal capture, display, and waveform synthesis package called 'Win-eLab'. The software is able to run on a conventional desktop or laptop with no additional hardware, and can perform real-time Fourier analysis on audio-frequency signals. This paper is intended as an introduction to Win-eLab, aimed at motivating further use of it in both teaching and self-directed learning contexts. The use of the software to familiarize students with the concept of 'laboratory' instrumentation is discussed, as well as the usefulness of a simultaneous time-domain/frequency-domain display for understanding signals, particularly in signal processing and communications systems courses. It is anticipated that applications may extend beyond electrical and electronic engineering - for example, as an aid to understanding mechanical vibrations, acoustics, and in other discipline areas.

Keywords computer instruments; educational software; laboratory work

Laboratory work is well entrenched in most, if not all, engineering curricula. This is ostensibly for two compelling reasons. The first is to give the student a practical grounding in the instruments, hardware or other apparatus which they might encounter in professional life. The second, perhaps more subtle reason, is to support the learning process itself: the theoretical work becomes grounded in practice; the practice, in turn, supports and motivates theory. This is not an isolated view: Edward concurred with Doughty's view that 'in engineering, practical experiments and projects lie at the heart of the relationship between meaning and understanding'.1,2 Somewhat paradoxically, Evans observed that 'many [engineering] students derive the least satisfaction and sense of achievement from the formal laboratory content'.3

We set out to implement a software instrument that would enable students to grasp the principles of electronic instrumentation, before actual laboratory sessions with real equipment commenced. However, it soon became apparent that a self-contained, PC-based instrument would allow students the opportunity to do much more than simply prepare for laboratory sessions. It would allow students to experiment with 'what-if' scenarios in signal analysis and communications systems, without the need for extensive initial grounding in theory. Once the theory is introduced, the displays may be interpreted in the light of the underlying theory. Such an approach has a sound basis in educational psychology. As discussed by Kolb,4 the Lewinian Experiential Learning Model proceeds in exactly this circular fashion, from concrete experience to reflections, to abstract generalizations, and testing of the underlying theory. Thus, using the PC instrument presented herein, learning is reinforced by practical experimentation - but not in the environment of crowded, rushed laboratory sessions, where there is little time for reflective learning.

Simulations and virtual instruments

The relationship between academic or theoretical treatment and practical or laboratory work is not always clear, particularly in the mind of the student. This is especially so in the distance-learning context, where theory and practice may be somewhat decoupled. We reasoned that, especially in the distance- or self-directed learning modes, reflective learning would be enhanced if students could access laboratory equipment in their own time and space. One often-used model for such reflective learning is the virtual laboratory (see, for example, Ref. 5). This learning paradigm certainly has its place, as do simulated or virtual instruments. In the distance education context, multimedia and Internet-based courseware also has widespread applicability.6 Our contribution is a PC instrument for self-directed learning which is not a simulation, but rather a fully functional audio spectrum analyser and signal generator.

Win-eLab: a PC-based instrument

Motivated by a consideration of the above factors, and realizing that students today typically have powerful PCs with audio input/output capability, we set out to develop a PC-based instrument that could provide signal analysis in real-time. It was not to be a simulation in any way: the software is the instrument. The primary goal was to provide a method for students to familiarize themselves with the underlying operational concepts of the oscilloscope, spectrum analyzer and signal generator, prior to undertaking 'real' laboratory sessions. However, during the course of the project, it became apparent that the software itself would be a powerful vehicle to enhance learning.

The software, dubbed 'Win-eLab', is designed to loosely emulate the 'look-andfeel' of conventional instrument control panels and displays, although emphasis is given to simplicity over extensive functionality (Fig. 1). Further thoughts on the user-interface and operational design - which we consider to be a crucial aspect if the software is to be successful as a learning tool - are discussed throughout the paper.