NE555 Timer Astable Circuit Calculator

Astable Oscillator Timing Values for NE555

Input Fields

Resistor 1

R₁

Ω

Resistor between Vcc and discharge pin

Resistor 2

R₂

Ω

Resistor between discharge and threshold pin

Capacitor C

C

µF

Capacitor connected between threshold and ground

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Your Results

High Time

Low Time

Total Period

Frequency

Duty Cycle

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NE555 Astable Circuit Formulas

$$T = 0.693 \cdot (R_1 + 2R_2) \cdot C$$ $$f = \frac{1}{T} = \frac{1.44}{(R_1 + 2R_2) \cdot C}$$ $$\text{Duty Cycle} (\%) = \frac{R_1 + R_2}{R_1 + 2R_2} \cdot 100$$

Where:

• $$T$$ = period (seconds)
• $$f$$ = frequency (Hz)
• $$R_1$$ = resistor from Vcc to discharge (Ω)
• $$R_2$$ = resistor from discharge to threshold (Ω)
• $$C$$ = timing capacitor (F)

These formulas are standard for configuring the NE555 timer in astable mode.

NE555 Timer Astable Circuit – Calculation Example

Given:

• $$R_1$$ = 1 kΩ
• $$R_2$$ = 3.3 kΩ
• $$C$$ = 10 µF = 0.00001 F

Calculation:

1. $$T = 0.693 \cdot (1000 + 2 \cdot 3300) \cdot 0.00001 = 0.693 \cdot 7600 \cdot 0.00001 ≈ 0.0527~s$$
2. $$f = \frac{1}{0.0527} ≈ 18.97~Hz$$
3. $$\text{Duty Cycle} = \frac{1000 + 3300}{1000 + 6600} \cdot 100 = \frac{4300}{7600} \cdot 100 ≈ 56.6\%$$

The NE555 timer is a highly stable IC for generating precise timing pulses. In astable mode, it oscillates continuously, making it perfect for applications like LED blinkers, tone generation, PWM control, and clocks. This calculator helps determine output characteristics based on resistor and capacitor values, enabling fast and accurate prototyping of oscillator circuits.