Your first gate

A signal that flips. One lever, one lamp, one surprise. Build a NOT gate — the simplest gate that actually does something.

What you'll learn

• What a logic gate actually is: a rule that turns inputs into outputs.
• Why a NOT gate is the smallest gate that's still interesting.
• How to connect a lever to a lamp through a single gate on the canvas.

The idea

Logic circuits are built out of tiny rule-machines called gates. The simplest one you'll ever meet is the NOT gate. Its rule is boring on purpose: if the input is ON, the output is OFF; if the input is OFF, the output is ON.

That flip — from high to low or low to high — is the foundation for every clever circuit in this course. Decoders, adders, memory cells, CPUs: all of them start with a gate that says "no".

The challenge

Wire a Lever labeled Input into a NOT gate, then send the gate into a Lamp labeled Output. When you flip the lever, the lamp should do the opposite of what you'd expect.

Tip — labels matter for this lesson's check. Click each component and rename your lever to Input and your lamp to Output before you hit Check solution.

Going deeper

A NOT gate on its own is useful, but the real power comes from chaining it with the gates you'll meet next: AND, OR, and XOR. Combine a NOT with any of those and you get its dual — NAND, NOR, XNOR — and from those, you can build anything a computer can compute.