GlenCalc

555 timer calculator

In the classic astable circuit, the capacitor charges through R1 + R2 and discharges through R2.

Your answer

Frequency6.871 Hz
Duty cycle52.4 %
High time76.23 ms
Low time69.3 ms

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How we worked it out

Updated as you change the numbers.

  1. High = 0.693(R1 + R2)C. Low = 0.693 R2 C. f = 1.44 ÷ ((R1 + 2R2)C).

Method and assumptions

The 0.693 factor is ln 2: the capacitor swings between 1/3 and 2/3 of the supply. The duty cycle is always above 50% in this circuit unless a diode bypasses R2.

Questions

What frequency do 1 kΩ, 10 kΩ and 10 µF give?

About 6.86 Hz with a 52.4% duty cycle.

Sources

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