NE555 Timer Calculator
Calculate frequency, duty cycle, and timing for astable and monostable 555 configurations.
Configuration
Results
Time HIGH—
Time LOW—
Period—
Frequency—
Duty Cycle—
💡 Usage & Formula
NE555 Timers are popular analog ICs that generate precise square waves (astable mode) or single-shot pulses (monostable mode).
Formulas:
- Astable Frequency:
f = 1.44 / ((R1 + 2 * R2) * C) - Astable Duty Cycle:
(R1 + R2) / (R1 + 2 * R2) - Monostable Period (Delay):
T = 1.1 * R1 * C
Usage: Choose the operating mode, enter your resistor and capacitor values, and view the resulting frequency, period, and duty cycle.
When you need it: Designing an astable oscillator or a monostable one-shot with the classic 555 — an LED blinker, a rough PWM source, a debounce delay, or a simple clock.
Worked example: Astable with Ra = 1 kΩ, Rb = 10 kΩ, C = 10 µF → f = 1.44 / ((Ra + 2Rb) × C) ≈ 6.9 Hz at a duty of (Ra + Rb)/(Ra + 2Rb) ≈ 52%. A monostable pulse is t = 1.1 × R × C.
Tips & gotchas:
- A standard astable duty is always above 50% because it charges through Ra+Rb but discharges through Rb only.
- A diode across Rb (charge path bypassing Ra) lets you reach 50% or below.
- Use a CMOS 555 (LMC555/TLC555) for low supply current, rail-to-rail output and higher frequencies.
- Decouple pin 8 and tie the control pin 5 to ground through 10 nF to keep the thresholds quiet.