Abstract:

In the COVID-19 pandemic it is essential that educational institutions continue to conduct the online learning process in electronic environments. COVID-19 posed new challenges for academic lecturers at the University of Plovdiv, so they continued to develop a set of e-learning tools that directly correspond to the syllabi of the respective courses.

The authors of this article share their experience in the online teaching of oscillator circuits, which are the main units of radio receiver and transmitter devices taught in the course "Fundamentals of Communication Technology".

Creating computer models of oscillator circuits with Multisim assists students in their examination and analysis. The learners gain a deeper understanding of oscillators with different types of frequency selective filter used in the feedback. Computer models allow for the demonstration of the operation of these devices under different criteria. With the help of virtual instruments, students perform real-time measurements of the amplitude, the frequency and the nonlinear distortions of the generated signals.

The article presents computer models of:
- RC Phase Shift Oscillator, implemented with Оp-amp TL 082CD;
- Colpitts oscillator, implemented with Оp-amp LM741CH;
- Wien Bridge oscillator with Frequency Control, implemented with Оp-amp LM741CH;
- Triangle & Square Wave Oscillator, implemented with Оp-amp OPA364ID.

The calculated and simulated readings of the measured parameters are presented and analyzed. The oscillograms of the generated signals of the oscillators under examination, observed with a virtual oscilloscope, are presented and compared. A time domain analysis is performed.

Using the free version of the NI Multisim software environment (Analog Devices Edition) provides an opportunity for the students to solve various problems which arise while they are mastering the lecture material and this makes the concepts taught more easy to understand.

The experience shared here is characterized by the fact that in the process of teaching oscillator devices, engineering students can quickly change the parameters of the elements and the configuration of the circuits, which allows them to visually demonstrate the result of real-time actions on a computer screen.

The developed electronic tools allow the lecturers to assign an individual project to each student, and the students to independently conduct the research required to complete the project.

The computer models of oscillatory schemes which are presented in this article, are developed and researched within the online learning environment, and they prepare the students for conducting more efficient experimental research with the models available in the university laboratories, according to a schedule that is consistent with the pandemic situation.

Keywords:

Oscillators, online learning, NI Multisim, student projects.