555 Timer Calculator

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Frequency, high and low time and duty cycle in astable mode, and pulse width in monostable mode — from R and C

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Enter the values

What to work out

Capacitance (C)

Result

Frequency (f)

6.857Hz

Duty cycle

52.381%

In this basic circuit the duty cycle is always above 50 %; a diode across R2 is used for lower duty cycles.

1.44 ≈ 1 ÷ 0.693, so f and 1 ÷ period agree up to rounding.

Working

Formulas

Assumptions

With the 555's 1/3 and 2/3 Vcc thresholds: 0.693 = ln 2 and 1.1 ≈ ln 3.
Capacitor tolerance and leakage shift the timing; check the allowed resistor and capacitor range in the chip's datasheet.

Sources: Robert Boylestad, Electronic Devices and Circuit Theory · Texas Instruments NE555 datasheet

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