555 Timer Calculator
How to use the 555 timer calculator
- Choose astable (oscillator) or monostable (one pulse).
- Enter R1, R2 for astable mode, and C.
- See the frequency, high and low times and duty cycle, or the pulse length.
Frequently asked questions
What are the formulas?
Astable: high time = 0.693 × (R1 + R2) × C, low time = 0.693 × R2 × C. Monostable: pulse = 1.1 × R × C.
Why is the duty cycle always over 50%?
In the standard astable circuit the capacitor charges through R1 and R2 but discharges only through R2. Add a diode across R2 for duty cycles below 50%.
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