Ohm Sweet Ohm

Light one LED without burning it out. That's the first bench. Thirty-four later you'll have built a working binary adder out of relays. Ohm Sweet Ohm is a real breadboard you can carry around. Push components into the holes, run wires between them, and the circuit is actually simulated: current flows, resistors limit it, and if you skip one your LED burns out in front of you. You start with a battery, a resistor and one LED, and work up through series and parallel wiring, Ohm's law, dimmer dials, switches, logic gates built from relays, capacitors that hold a circuit open after you let go, binary and hexadecimal, and finally a full adder—the circuit at the heart of every computer that has ever done arithmetic. Every bench explains the idea behind it in plain language. Why a resistor is needed at all. Why series shares current and parallel shares voltage. Why a capacitor makes a delay…