The 555 Timer

A capacitor that blinks

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• The 555 charges a capacitor between ⅓ and ⅔ of the supply voltage.
• Each stage lasts ln 2 ≈ 0.693 time constants.
• Astable frequency f ≈ 1.44 / ((R₁ + 2R₂)C).

Steps

1. Charging between two thresholds
2. How fast does it tick?
3. Blink once a second
4. Where does ln 2 come from?
5. On for how long?
6. A quick pulse