555 Monostable Mode

A falling edge on pin 2 (below ⅓ $V_{CC}$) sets the output high; it stays high while the capacitor charges through $R$ to ⅔ $V_{CC}$:

$T = 1.1\, R\, C$

Example: R = 100 kΩ, C = 10 µF → $T$ ≈ 1.1 s. Uses: timers, missing-pulse detectors, switch debouncing and pulse stretching.