Stop reading about circuits. Start turning the knobs.
The textbook is free and open. This site is where you use it — every chapter gets circuits you can change, breakers you can trip, and practice problems that generate fresh numbers every time so you can't memorise your way out.
Consequences, not answers
Switch on the hair dryer and the breaker actually trips. Short out a branch and watch the power stop reaching three elements. The circuit reacts, so the rule sticks.
New numbers, every time
Every drill regenerates its own values. You can run the same exercise ten times and get ten genuinely different problems — the way practice is supposed to work.
Signs made visible
The book warns that ignoring direction and polarity “is the cause of many sign errors.” So the exercises here mark where your sign went wrong, not just that it did.
The thirteen chapters
Chapter 1 is live now. The rest follow the same shape: a short recap of what you need, then a set of interactives — simulators to build intuition, drills to build speed.
Electrical Engineering Fundamentals
Maryam A. Al-Othman, John H. Cole, and Dimitrios Peroulis · Purdue University Press, 2025
The textbook for ECE 20001 at Purdue University. Its authors decided it should be free for everyone — this companion follows the same principle. Nothing here replaces the book; it gives you somewhere to put the ideas to work.