The NOT Gate
The NOT gate, or inverter, is the simplest logic gate: it takes one input and outputs its opposite, true becomes false and false becomes true. Applying an inverter twice returns the original signal unchanged, a property circuits rely on when they need to reverse logic partway through a design. An advanced companion to Andy, Orla, and Nottie Team Up, naming the real term directly for an older audience instead of the character Nottie.
Say on, and the inverter answers off. Say off, and it answers on. One input only, a single rule small and true, whatever signal enters, the inverter turns it through.
High becomes low. Low becomes high. True becomes false. False, in reply.
Wire it after a switch, and a light works backward now, press the button down, and the bulb, once bright, goes dark.
Bubble drawn on a gate's own symbol marks this flipping act, a single circle turning true to false, and false right back.
Every input finds its mirror the instant it walks through the door, the inverter keeps one promise only: never the same as before.
Stack two inverters together, and the signal returns unchanged, flip it twice, and the signal lands right back where it began.
On, off. Off, on. High, low. Low, high. The simplest gate of all answers opposite, and says goodbye.
Key Concepts: The NOT gate (inverter) takes one input and outputs its logical opposite | True becomes false and false becomes true, high voltage becomes low and low becomes high | Applying an inverter twice in a row returns the original signal unchanged | The NOT gate is the only basic gate with a single input, distinct from AND, OR, and XOR
Key Words: NOT gate, inverter, logical negation, single input, invert
Advanced companion note: This is the real-term companion to Nottie in and-or-not-team-up.md, written for an older audience directly about the NOT gate rather than through the character.