555 Timer (Astable)

The 555 is the most famous chip ever made. Set two resistors and a capacitor and watch it oscillate — the beating heart of blinkers, tones, and clocks.

555 Timer (Astable)Live

the classic square-wave oscillator

Controls

Presets

R1 (kΩ)

R2 (kΩ)

C (µF)

In astable mode the 555 oscillates on its own, charging the capacitor through R1+R2 and discharging through R2. Frequency f = 1.44 / ((R1+2R2)·C), and the duty cycle always exceeds 50% for this classic circuit. Educational tool.

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Data Inspector

Frequency1.4 Hz

Duty cycle55%

High time395.01 ms

Low time325.71 ms

Governing equation

f = \frac{1.44}{( R _{1} + 2 R _{2} ) C} = 1.4 Hz, D = \frac{R _{1} + R _{2}}{R _{1} + 2 R _{2}} = 55%

Reading this result: A slow 1.38 Hz output (period 0.72 s) suits an LED blinker; the large 10 µF capacitor dominates the timing.

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How it works

In astable mode the 555 charges a capacitor through R1+R2 and discharges through R2, producing a square wave at f = 1.44/((R1+2R2)·C). Because charge and discharge use different paths, the duty cycle always exceeds 50%. Educational tool.

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Frequently asked questions

Is this 555 timer astable calculator tool really free?▾

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No. Everything runs client-side in a modern browser — no downloads, no license, no account required to start.

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How accurate are the results?▾

The solver uses established numerical methods, but results are for research and educational purposes and should be validated against experiment or professional review before you rely on them.