555 Timer Calculator | Astable & Monostable Mode

Formula

This calculator uses the standard 555 timer calculator formula:

Astable Frequency Formula

f = 1.44 / ((Ra + 2×Rb) × C)

Frequently Asked Questions

What is a 555 timer? ⌄

The 555 timer is a versatile integrated circuit used to generate precise time delays and oscillations. It operates in three modes: astable, monostable, and bistable.

What is astable mode in 555 timer? ⌄

In astable mode, the 555 timer continuously oscillates, producing a square wave output. Frequency = 1.44 / ((Ra + 2×Rb) × C).

What is monostable mode in 555 timer? ⌄

In monostable mode, the 555 timer produces one output pulse of defined width when triggered. Time delay = 1.1 × Ra × C.

How do I calculate the duty cycle of a 555 timer? ⌄

Duty cycle = (Ra + Rb) / (Ra + 2×Rb) × 100%. To get 50% duty cycle, use a diode in parallel with Rb (so charging goes through Ra only).

How do I change the frequency of a 555 timer? ⌄

Frequency f = 1.44 / ((Ra + 2Rb) × C). Increase C or R values to lower frequency; decrease them to increase frequency. Frequency is inversely proportional to both.

What capacitor value gives 1 Hz with a 555 timer? ⌄

For 1 Hz: 1 = 1.44/((Ra+2Rb)×C). With Ra=Rb=47kΩ: C = 1.44/((47k+94k)×1) = 1.44/(141,000) ≈ 10.2 µF. Use a 10 µF capacitor with fine-tune resistors.

⏱️ 555 Timer Calculator