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.