How does a calculator work?

Open a pocket calculator and you find rubber keys with carbon pills, a circuit board with a grid of pads, one chip under a blob of black epoxy, an LCD, and a solar cell with a button cell for backup.

Read how it works: How does a calculator work? · The history of the calculator · More boxes on Glassbox

Chapters in this interactive model

1. Inside a pocket calculator: Twenty rubber keys, one chip, one display and a solar cell the size of a stamp.
2. From a key press to binary: The chip scans a grid of wires to find your key, waits out the bounce, and stores the digit as 4 bits.
3. Switches that make decisions: A transistor is a switch worked by electricity. Wire a few together and you get gates: NOT, AND, OR, XOR.
4. Adding with logic gates: Two gates add two bits. Five add three. Chain four and the carry ripples from bit to bit.
5. Seven segments of liquid crystal: A digit is seven bars. Each bar is a sandwich that twists light, until a small voltage stops the twist.
6. Sunlight, and the last digit: Why a stamp-sized solar cell is enough, why 1 ÷ 3 × 3 isn't always 1, and how sin and cos come from adding.