Glad you asked!

Let me begin by explaining why I wanted to write an interactive ebook and not a print book on Feedback Control Systems. I know from personal experience that control system theory is a difficult subject to learn. It is often taught at the college level in the senior year or later in graduate school. Most textbooks on this subject are difficult to understand unless the reader has a firm grip on higher mathematics subjects, including, at a minimum, differential equations and complex variable theory. I might also mention that these textbooks typically cost well over a hundred dollars. Difficult math and high cost of textbooks are barriers to learning a subject that I believe can be taught to technicians, all types of engineering students, and any practicing engineer who never had a course in feedback controls.

Textbooks filled with graphs and equations are not, in my opinion, the way to teach or learn control system theory. I wanted to explore new methods for teaching this subject, as it is my passion to make it easier for anyone wishing to learn difficult engineering subjects like feedback control systems.

**About Apple iBooks Author**

It wasn't until Apple came out with their iBooks Author program that I got excited about producing interactive ebooks. I saw in this authoring program an alternative way to teach control system theory. I previously converted my first book, Modeling Engineering Systems, into an ebook using the Kindle Format 8 and the Apple ePub 2 format, so I knew the limitations of these formats. The biggest limitation of these formats is they can for the most part only render equations as bitmaps. This means that equations will not resize as the reader resizes fonts. Another major drawback is these formats have only the simplest kind of interactivity (embed a video and link to another page in the book, to name two). They cannot handle embedded interactive simulations written in JavaScript. Mainly for these two reasons, I turned to Apple iBooks Author to develop my new feedback control systems ebook because iBooks Author could accept MathML, (and in my case) MathType, and I could develop interactive widgets (dynamic simulators, root locus plotter, etc.) using JavaScript and HTML. Both scalable equations and interactive simulators could be directly embedded into my ebook. With iBooks Author I could now engage students with many interactive elements. This, I hope, will allow students to make discoveries on their own, and allowed me to eliminate countless static graphs from the ebook.

Feedback Control Systems Demystified iBook turned out to be exactly what I wanted. Text, equations, videos, enhanced root locus plotters, open loop and closed loop simulators, workbooks, quizzes and more are all embedded into the ebook and are available at the touch or swipe of a finger. I wanted to get the book out to everyone who wanted to learn about feedback control systems, but there was a problem. iBooks originally could only be viewed on an Apple iPad. Shortly after I released the book, Apple made an iBooks reader available for Apple desktops and laptops that use the latest Apple operating system. I have hopes that Apple will soon make the iBooks reader available for Windows-based systems, much like they do now with QuickTime and iTunes. Unfortunately, Apple has not at this writing made the iBooks reader available for Windows computers or Google-based tablets. Amazon, on the other hand, has made the Kindle ebook reader available for just about every computer operating system. As a result, Amazon Kindle ebooks far outsell Apple iBooks. From an author's point of view this is unacceptable.

**About Kindle Format 8**

How then could I produce a Kindle version of Feedback Control Systems Demystified and still retain all the interactivity I considered so important to teaching this subject? I clearly could not embed all the interactive elements because the Kindle format does not allow resizable equations or embedded JavaScript coding. Kindle Format 8 claims to support SVG (scalable vector graphics), but I found it very difficult and time consuming to use SVG with equations. In the end, I used extra large bitmaps for my equations. Kindle Format 8 does allow a user connected to the web to link to a page on a website. Kindle readers creates an overlay that shows the website page and a "Done" button which the reader can select to remove the web page and reveal the underlying page of the ebook. This gave me the idea that I could move most of my interactive elements to my book website. After some experimentation, I was able to place most of my interactive elements on the web. About the only interactive elements included in the iBooks version that are not included in the Kindle ebook are the interactive quizzes. To handle the equation sizing problem, I decided to make each equation as large as possible so they were clearly readable. I did this because I have found so many engineering textbooks converted (mostly by major publishers) for the Kindle that are loaded with equations you cannot read. The same comment applies to many tables and graphs in these converted ebooks. So I made sure that all my tables and graphs could be enlarged and clearly readable.

Unlike the Apple iBooks version of Feedback Control Systems Demystified, the Kindle Format 8 version requires the reader to be connected to the internet to enjoy the full interactivity. So although you can't access all the interactive elements unless you have an online connection, you can read it on any computer/notebook/tablet that has the Kindle Reader installed. Here are links for a few examples taken from the Kindle version of Feedback Control Systems Demystified.

Sample Workbook

Sample Dynamic Circuit Simulator

Sample Enhanced Root Locus Plotter (click and drag the slider)