About
Welcome to Spinning Numbers. The topics covered here are what you will find in an undergraduate electrical engineering course on circuits. My goal is to explain things to you as a good friend who wants to help you understand these elegant ideas.
I got interested electricity when I was about eight years old. My first sense of wonder came from a tube radio. This glowing box played music sent on invisible waves from miles away. Are you kidding me! How great is that! How did someone figure that out? Electricity is invisible, and yet people understand it and can invent radios and other great stuff. I wanted to understand, too.
In college I majored in electrical engineering. My career began designing integrated circuits and computers for TRW and Hewlett-Packard. Later on I got to work at Agilent Technologies on DNA and protein measurement, and then two exciting medical device startup companies.
I had a great year as a Content Fellow at Khan Academy. Sal and the other content creators taught me the approach to teaching in the KA style.
Here at Spinning Numbers I have been improving the articles based on questions from learners, and writing new articles as well. The videos are mostly the same ones you see on KA EE.
All through my career, for each new project I would go back to my college textbooks to re-study the fundamentals I needed. Years after graduation there were moments I would slap my head and say, “So that’s what my teacher meant!” My goal is for these videos and articles to help you to have similar head-slapping Aha! moments, but without the long years in between.
Circuit sandbox
Circuit simulation is a critical tool for engineers. A special feature at Spinning Numbers is the Circuit sandbox simulator. You can study circuits by simulation and try out your own ideas.
Under the hood
This site is saved at GitHub, hosted by GitHub Pages. The site is generated by Jekyll using the ‘minima’ theme. GitHub provides a free ssl security certificate (https) to protect user information.
The articles are written in Jekyll’s Kramdown, a superset of Markdown. I use home-grown templates for positioning images and to create <details> tags in markdown files (the hints that appear everywhere in articles),
Equations are beautifully rendered by $\KaTeX$, the super-fast math typesetting library from Khan Academy.
Drawings of circuits and other images come from Adobe Illustrator and Inkscape. Here are my home-grown schematic symbols.
Animated images and computed graphs are created with D3.js. The source code for animations and graphs are in the /assets/d3 folder.
Videos are drawn in Sketchbook Pro. The screen and audio are captured and edited in Camtasia. I use a Wacom Bamboo tablet, and a Sampson USB microphone.
Comments are implemented with Staticman running at Heroku, with protection from scalawags provided by reCAPTCHA. If you contribute a question, comment, or reply, you can optionally enter your email address to be notified of new comments. The notification email is sent by Staticman using a secure private email service provider, MailGun. Your address will only be used for notifications. You may unsubscribe at any time.
My write-up on implementing [Staticman at Heroku[(https://spinningnumbers.org/a/staticman-heroku.html).
Acknowledgments
I’m grateful to Sal Khan and everyone at Khan Academy for the inspiring vision of a free world-class education for anyone, anywhere.
Questions
Thank you for the circuit, it’s the only thing I understand in my classes
Love your stuff man! Keep up the amazing work!
why don’t you make posts on mathematics as you have a good command over it.
Dear Mr. McAllister,
First of all, let me thank you for all this incredible content. I would like to ask you if you could recommend any sources for practicing (ideally with worked solutions) the principles thought in this series. I feel I understand the theory fairly well but I know the real questions arise when you start working on problems on your own.
Looking forward to hearing from you. Kind regards,
Filippos, I’m glad you are enjoying the site. My suggestion for practice is to revisit the articles on DC Circuit Design and collect all the example circuits on paper. Then solve each circuit using as many Methods as you can remember. Node Voltage, Mesh Current, Superposition, Fundamental Laws (winging it), Source Transformation. Also, modify the resistor and/or source values and do it again. Sometimes you can get a current to reverse itself in a resistor by picking different component/source values. Try this on the Floating Voltage Source at the end of Node Voltage Method article. Apply Thevenin’s Theorem to a few of the sample circuits. Pick a port anywhere you like, and derive the Thevenin and Norton equivalent. To check your work, use the Circuit Sandbox as a second opinion on the solution. Don’t Cheat by using the simulator first.
Thanks so much for the videos and articles! I’m an IT graduate who found a love for electronics, but only studied high school physics and felt really lost. Your teaching style is really engaging and I definitely feel like I’m learning a lot from you!
What textbooks or other resources would you recommend a beginner? I wonder if you’ve ever thought about writing your own book on EE! :)
Cherie, Thanks for your kind comment. For other resources I suggest you visit a nearby college or university bookstore. Find out which text is used in the introductory EE circuits class. Look for the MIT online class 6.002 Circuits by Agarwal, or 6.003 Signals and Systems. https://ocw.mit.edu/courses/find-by-number/ Another resource is Digikey or Mouser, both excellent suppliers. Buy a powerful microprocessor development board for less than $10. Look for ARM or Arduino or Raspberry. Dream up a gizmo and create it. Water your plants, scare squirrels, build a robot.
As you work through the DC Circuit Analysis section, make a collection of all the example circuits. Then go back over them and solve each one using as many Methods as you can remember.
When I think about writing a book I worry about how to fix mistakes in paper copies already sold. I like web publishing because I can fix or improve something in minutes. But who know, maybe someday I’ll commit to a book.
Thank you for doing this. Do you recommend someone who is learning study these pages, the KA ones, or both?..?
Robert - Welcome to spinningnumbers. Here are the pro’s and con’s for using this site vs KA.
As of right now, the videos are all the same. My new year’s resolution is to add new videos to spinningnumbers. in the coming year.
Pro’s for spinningnumbers…
All of the articles I wrote for KA have been reviewed and improved and posted to spinningnumbers. There are some new articles here that don’t appear on KA. (The first example is Charge at the top of the introduction section.) Spinningnumbers has a circuit simulator (Circuit Sandbox) that KA does not. The Sandbox has been integrated into several articles to help you understand the concepts. This is a great learning tool. If you find an error in a spinningnumber article or video, I can fix it in a few minutes.
Pro’s for KA…
KA has a sophisticated point tracking and badge-awarding system that keeps track of your progress. Spinningnumbers does not. The webmaster is me and I don’t know how to do that stuff. KA has a few other volunteers besides myself who answer questions. But the lion’s share of EE answers still come from me.
I hope you enjoy your learning experience here.
Took EE101 40 years ago but went into software. Finally have time to go through the KA refresher. Great job! Thanks. Looking forward to the rest of the course;-)
Jon, Welcome to spinningnumbers. The articles you find here are all freshened up and improved compared to the ones on KA with a similar title. Many articles included simulation models so you can fiddle with the circuits yourself. So far, the videos posted here at spinningnumbers are the same ones I did for KA. I hope you enjoy your studies. Please ask questions and let me know what works and what doesn’t as far as making the ideas understandable.
I’m studying your course in Khan Academy. I would like to express you my gratitude an my intention of take advantage too of these materials you offer us.
Thank you, you are an awesome teacher!
Fernando - Thank you! And welcome to Spinning Numbers. I’m working hard to update and improve all the articles you find in KA’s EE section. Then I hope to create more videos. I would love to hear your comments on anything you think can be improved.
Very interesting. Will(y)! definitely look into it as I would to understand what EE colleagues’ cryptic “sign language”
PS: little typo above “Available”
Thanks Remy. I fixed the typo. I hope the sign language becomes less cryptic and more “oh, yeah, sure”.