Electronics with Discrete Components

Book Preface

This text is designed for a one-semester course on electronics. Its primary audience is second-year physics students, but it can include students from other disciplines or levels who understand elementary notions of circuits and complex numbers. Most physics programs, especially those in liberal arts colleges, can afford only a one-semester course in electronics. Electronics is a vital part of a curriculum because it trains students in a basic skill of experimentation. With this knowledge, students can design circuits to manipulate electronic signals or drive mechanical devices. An electronics course also gives students a basic understanding of the inner workings of electronics instruments. Thus, an electronics course prepares students for advanced laboratories and, ultimately, experimental research.
Because of the nature of the topic, the course must have a huge hands-on component. Electronics is learned by experience. At Colgate University, we have been teaching a course that meets two days a week, with a one-hour lecture followed by a two- to three-hour lab. In the lab, students build circuits that closely follow the topic of the class. We have put special effort into making those labs instructive but at the same time interesting, empowering, and fun. We made a special effort to introduce transducers in the labs, highlighting applications. Today’s students live around black boxes, mostly ignorant of the circuits that lie within them. Our recent experience tells us that students find the discovery of how those boxes work, or even the task of building them, extremely interesting, rewarding, and useful. Thus, we can use this “revelation’’ as a way to motivate students to learn electronics.
Instructors who adopt this text may have labs in place and may not have use for the labs in this book. However, the experiments listed may give instructors ideas to renew or modify the labs in place. In addition to the normal curricular plan, we devote two weeks in the middle of the semester and two weeks at the end of the semester to unscripted projects, in which students design the device of their choice. This is where students learn tremendously and enjoy the experience. Their ambition to build the device of their choice pushes them to invest much energy and time, and along the way, they learn invaluable aspects of building devices, such as creating new designs and troubleshooting. In the first project, students do mostly digital work (more on this choice below), but they still use a little bit of analog, because they need switches or pushbuttons for digital inputs and light-emitting diodes (LED) for digital outputs. In the second project, students do mostly analog work, but they can combine analog and digital electronics. Whatever the case, students end up doing amazing projects. Some of the analog projects can be combined with real computers, but this is an aspect that we do not cover here. If lab PCs have interface cards, the projects will be more powerful. A word of caution from experience: Make sure that the project does not become a computer project. Although knowing programming is not that bad of a goal these days, it is not the objective of this course.
The text is divided into two parts: digital and analog. In each part, we cover the essential components needed to understand and design circuits with discrete components. We cover the digital part first. This may seem like heresy to some instructors, but I urge them to re-consider the concept. Covering digital first makes sense because digital electronics focuses mostly on logic. The topic is not as intellectually demanding as analog. Besides a few rules of thumb for wiring, students have little need to know about the currents that flow through the gates or even the analog circuits that make up those gates. Later in the semester, after covering the analog part, the class revisits the details of gates. The digital part is demand-ing on wiring practices, but not on conceptual understanding. This way, students get early exposure to demanding circuits and are forced to embrace systematic wiring practices. By the time students reach analog, they no longer have trouble wiring and powering circuits. It makes sense to cover analog after digital because students end with the understanding of the complexity and importance of analog. Otherwise, students would get the wrong message: Since analog is not needed to do digital, it is unnecessary altogether. An instructor who strongly disagrees with this strategy could swap the two parts without major logistic com-plications, but he or she would have to continue to emphasize analog concepts throughout the digital part.
The content of this text borrows ideas on the organization of topics from two classics in the field: Digital Design, by M. Morris Mano, and The Art of Electronics, by Paul Horowitz and Winfield Hill. The chapters are designed so that they take an integral number of days. Labs may also extend one day, and in digital, several labs build upon the circuit of the previous lab. The topics of the specific chapters go as follows. The first chapter, “The Basics,’’ reviews the fundamentals of electricity and electrical components. It brings the student, especially the nonphysics major, up to speed with the physics and basics of electric circuits. The second chapter, “Introduction to Digital Electronics,’’ covers digital signals and electronic gates. It is followed by two chapters on combinational logic, namely “Combinational Logic’’ and “Advanced Combinational Devices.’’ They are followed by a chapter titled “Sequential Logic,’’ which emphasizes counting circuits, and an important application in memory. Throughout this part, we include tables of integrated circuits that are useful for designing circuits. A rack of ICs of various types is vital in an electronics lab. The lab exercises use a “logic board,’’ which is a homemade or commercial box with switches that generate input states, and LEDs to display output states. Appendix A gives the details of this device and its construction. Some versions of these boards are commercially available. If time permits, the instructor may consider other adventures, such as microcontrollers and interfacing using Labview, but such endeavors are specialized to particular equipment for which there is no uniform agreement. Instead of attempting a partial or incomplete description, we do not cover those at all.

The analog part starts with the chapter “AC Signals.’’ It covers a more sophisticated analysis of circuits than the first chapter and centers on the use of complex numbers for defining signals and impedances. We find this advantageous and practical. To complement this, we include a short introduction to complex numbers. It ends with an important concept to students: Thevenin equivalent circuits. Throughout, this part reduces circuits to single-loop modules, building up the concepts of input and output impedance. We follow with the chapter “Filters and the Frequency Domain,’’ where the role of frequency and frequency response comes to the surface. The use of multiple filter stages underscores the role of source and load impedance. At the end of this chapter, we insert a section on Fourier Series. This is important because electronics’ processing of signals can be understood easily at the single frequency level. Therefore, knowing the decomposition of a complex signal into its frequency spectrum is vital in understanding the frequency response of a circuit. This part can be skipped if the curriculum already contains Fourier series. The chapter that follows, “Diodes,’’ starts with a physical explanation of semiconductors that gives the student an intuitive and informed basic understanding of the physics of these materials. It emphasizes nonlinear responses and the use of the load line, and ends with an application on the design of power supplies, among other diode tricks. The chapter titled “Transistors,’’ covers both bipolar-junction and field-effect transistors. Because operational amplifiers are much better suited for signal conditioning, we do not cover in detail some of the traditional circuits on biasing the transistor. Increasingly, modern devices use field-effect transistors instead of bipolar transistors, so we give both nearly equal coverage and focus on power drivers, followers, and current sources. These are applications that even operational amplifiers cannot deliver and in which transistors have rightful place. The final part of analog is the experimenters delight: “Operational Amplifiers.’’ We give ample coverage to numerous circuits, plus we use them to smuggle in other interesting topics, such as comparators and feedback. We wrap up with a chapter that interfaces digital and analog signals and transducers, in “Connecting Digital to Analog and to the World.’’
At the end of most chapters is a section titled “Lab Projects’’ that contains many interesting circuits that have been proven to work well for instruction. Many of them have interesting twists that make the experience a fun one. I like to follow this motto: “Let the kids have fun.’’ If they do, they will learn electronics. Our tests also have a practi-cal component. When students work in groups there is a danger that they are passive and let their partner(s) do valuable laboratory know-how. To force them to be active participants, we test them individually on building simple circuits. The final section of each chapter is titled “Practicum Test.’’ It gives questions that we have often asked on simple aspects of the lab that students should know. This includes powering components and diagnosing signals with the oscilloscope. The goal is for each student be able to do every task and not leave any activity, and know-how, to his or her partner.
I owe immense gratitude to Joseph Amato. Together we designed this course almost 20 years ago. His prolific expertise and creativity led to the design of a number of lab experiences described in this text. I also want to thank Wes Walters for selling me the idea of covering digital before analog; Dave Glenar, Ken Segall, and Steve Slivan for ideas for labs and problems; Juan Burciaga and Danielle Solomon for useful suggestions and edits; Timothy Kidd, M.K. Kim, Bryan Suits, Christos Velissaris and other anonymous reviewers of the drafts of this book for their valuable advice; and Samantha and Daniel Galvez for helping Dad with aspects of this project.