Preface

The idea for this book first occurred while teaching audio electronics, where basic concepts were proving difficult to explain quickly enough to allow audio amplifier and filter projects to be built. Thus, many students would struggle with the fundamentals and then lose interest before the more interesting circuits could be discussed. There are many good books on audio electronics that require a prior knowledge of electronic circuit theory and conversely the books that discuss these theories do not cover audio in detail. Similarly, there are many good audio project tutorials available, but they do not introduce fundamentals like programming and system control. After trying to teach theory before project, then project before theory, it was becoming clear that a text combining both in a series of smaller steps would be more useful – the chapters in this book are those resulting steps.

The Arduino is a great learning resource, and this book tries to use it to get circuits built quickly whilst introducing audio electronics fundamentals. Part of the reason for this is the large user base for Arduino – there are many great resources available that significantly extend the concepts introduced in these chapters. In addition, DC circuit theory is much easier to learn when building circuits, and the Arduino can quickly extend these circuits into digital control systems. In this book, building MIDI circuits is a great way to put DC circuit theory into practice and there is significant scope to progress beyond the MIDI drum trigger that represents the first milestone project.

The second half of the book uses AC circuit theory to introduce capacitors, which are fundamental to time-varying signals and can often be the ‘extra’ components in an audio circuit. Although this is only an introductory text, amplification and filtering circuits are arguably much easier to learn when the role of capacitors in DC blocking, AC decoupling and load balancing is also understood. Many students spend significant amounts of time starting at schematics for well-known pedals and amplifiers, thinking that those circuits are unbelievably complex. In reality, these circuits often take simpler amplification and filtering principles and combine them with practical techniques for stability and noise reduction (mostly capacitors) – the reality is much less complex than the circuit may initially suggest. It is partly for this reason that some transistor theory is included in the text – though it is provided for information rather than application. Many classic effects pedals use transistors, but operational amplifiers are a much better option for modern circuits.

In combining audio circuits with Arduino control, the main aim of this book is to show how digital control of analogue signals is a rich area of potential investigation. It is argued that this is not well covered by existing texts, even though most commercial audio equipment incorporates these techniques. The final project in chapter 9 is much more complex (and challenging) than any of the previous chapters, but it helps to underline how quickly the Arduino can be used for control in an audio circuit. If you work through the book it is hoped that you will finish chapter 9 with lots of ideas for potential circuits of your own – this is where electronics becomes really interesting!