IC 555 Astable Timer Calculator

555 Timer Frequency and Duty Cycle Estimator

Input Fields

Resistor 1

R₁

Ω

Resistor connected between Vcc and discharge pin

Resistor 2

R₂

Ω

Resistor connected between discharge and threshold pin

Capacitor

C

µF

Capacitor connected from threshold to ground

CalculateReset

Calculate automaticallyIf enabled, the result will update automatically when you change any value.

Your Results

Time High

Time Low

Total Period

Frequency

Duty Cycle

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Astable Mode Output Formulas

$$f = \frac{1.44}{(R_1 + 2R_2)C}$$ $$T = \frac{1}{f}$$ $$\text{Duty Cycle } (\%) = \frac{R_1 + R_2}{R_1 + 2R_2} \cdot 100$$

Where:

• $$f$$ = frequency (Hz)
• $$T$$ = period (s)
• $$R_1$$ = resistor between Vcc and discharge pin (Ω)
• $$R_2$$ = resistor between discharge pin and threshold pin (Ω)
• $$C$$ = capacitor between threshold and ground (F)

These formulas define how the 555 timer behaves in continuous oscillation (astable) mode.

IC 555 Astable Timer – Calculation Example

Given:

• $$R_1$$ = 10 kΩ
• $$R_2$$ = 4.7 kΩ
• $$C$$ = 100 nF = 0.0000001 F

Calculation:

1. $$f = \frac{1.44}{(10,000 + 2 \cdot 4700) \cdot 0.0000001} = \frac{1.44}{19,400 \cdot 0.0000001} = \frac{1.44}{0.00194} ≈ 742.27~\text{Hz}$$
2. $$T = \frac{1}{742.27} ≈ 0.001347~s $$
3. $$\text{Duty Cycle} = \frac{10,000 + 4700}{10,000 + 2 \cdot 4700} \cdot 100 = \frac{14,700}{19,400} \cdot 100 ≈ 75.77\%$$

The 555 timer in astable mode continuously switches between high and low states, making it ideal for generating clock pulses, blinking LEDs, and tone generation. This calculator simplifies the configuration process by letting you input resistor and capacitor values to get exact output frequency, time period, and duty cycle. It’s an essential tool for students, engineers, and hobbyists working with analog and digital timing circuits.