Vol. IV — Electronics · Tool
NE555 astable and monostable. Change R and C — frequency, period, duty, and pulse width update as you type. Classic bipolar formulas.
Astable (free-run): timing capacitor charges through R1+R2 and discharges through R2 alone. Datasheet shortcuts: f ≈ 1.44 / ((R1 + 2·R2)·C), Thigh ≈ 0.693·(R1+R2)·C, Tlow ≈ 0.693·R2·C. Duty is always above 50% in this wiring unless you add a discharge diode.
Monostable (one-shot): a trigger starts the pulse; width T ≈ 1.1·R·C until the capacitor reaches 2/3 Vcc.
Pair with RC time for τ marks, Resistor codes and Capacitor codes to pick parts. Back to the electronics bench.