555 timer calculator

Astable frequency and duty from R1/R2/C, monostable pulse width, and an E24 resistor picker for a target frequency.

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Standard bipolar 555 formulas; duty is always above 50% in astable. Component tolerance is not modeled — verify on the bench.

How to use

  1. Choose astable or monostable.
  2. Enter R1/R2/C to get frequency and duty, or set a target frequency to pick resistors.
  3. Read the timing values.

What it supports

Standard bipolar 555 formulas: astable f = 1.44/((R1+2R2)C), monostable t = 1.1·R·C for 1 µs–3600 s pulses. Resistors 100 Ω–100 MΩ, capacitors 100 pF–10,000 µF, astable targets 0.01 Hz–500 kHz. Duty in astable is always above 50%.

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