555 Timer Calculator
Calculate frequency, duty cycle, and timing for 555 timer in astable mode
Kilohms (kΩ)
Kilohms (kΩ)
Microfarads (µF)
How to Use This Calculator
Enter Resistor Values
Enter R1 and R2 in kilohms. R1 is between Vcc and discharge pin, R2 is between discharge and trigger/threshold pins.
Enter Capacitor Value
Enter the timing capacitor value in microfarads (µF). This capacitor charges through R1+R2 and discharges through R2.
Get Results
Click calculate to see output frequency, duty cycle, high time, and low time for the 555 timer in astable mode.
Formula
Thigh = 0.693 × (R1 + R2) × C
Tlow = 0.693 × R2 × C
f = 1 / (Thigh + Tlow)
Duty Cycle = (Thigh / T) × 100%
Where:
- Thigh = High time (output ON) (s)
- Tlow = Low time (output OFF) (s)
- R1, R2 = Resistors (Ω)
- C = Capacitor (F)
- f = Frequency (Hz)
Example:
R1 = 10 kΩ, R2 = 10 kΩ, C = 10 µF
Thigh = 0.693 × (10,000 + 10,000) × 10×10⁻⁶ = 0.1386 s
Tlow = 0.693 × 10,000 × 10×10⁻⁶ = 0.0693 s
f = 1 / (0.1386 + 0.0693) = 4.81 Hz
Duty Cycle = (0.1386 / 0.2079) × 100 = 66.7%
About 555 Timer Calculator
The 555 Timer Calculator helps you design 555 timer circuits in astable (oscillator) mode. The 555 timer is one of the most popular integrated circuits, used for generating square waves, pulses, and timing signals. This calculator determines frequency, duty cycle, and timing parameters based on resistor and capacitor values.
When to Use This Calculator
- Pulse Generation: Design circuits for generating pulses and square waves
- LED Flashing: Create blinking LED circuits
- Clock Signals: Generate clock signals for digital circuits
- Educational Purposes: Learn about 555 timer operation
Why Use Our Calculator?
- ✅ Accurate Calculations: Uses correct 555 timer formulas
- ✅ Multiple Outputs: Shows frequency, duty cycle, and timing
- ✅ Easy to Use: Simple interface
- ✅ Free Tool: No registration required
Common Applications
LED Flashing: 555 timers are commonly used to create blinking LED circuits. A typical setup with R1=10kΩ, R2=10kΩ, C=10µF gives about 5Hz (5 blinks per second).
Pulse Generation: Generate square wave pulses for digital circuits, clock signals, and timing applications.
Tips for Accurate Results
- Enter resistances in kilohms (kΩ)
- Enter capacitance in microfarads (µF)
- Duty cycle is always > 50% (cannot achieve < 50% with standard astable circuit)
- For 50% duty cycle, use monostable mode or external modifications
- Larger R and C values = lower frequency
Frequently Asked Questions
What is astable mode?
Astable mode creates a continuous square wave oscillation. The 555 timer switches between high and low states continuously, creating a clock signal. No external trigger is needed.
Why is duty cycle always > 50%?
In standard astable configuration, the capacitor charges through R1+R2 (longer) and discharges through R2 only (shorter). This makes high time longer than low time, giving duty cycle > 50%.
How do I get 50% duty cycle?
For 50% duty cycle, use monostable mode, add a diode across R2, or use a different circuit configuration. The standard astable circuit cannot achieve exactly 50%.
What's the typical frequency range?
555 timers can operate from less than 1 Hz to over 500 kHz, depending on R and C values. Very low frequencies require large capacitors, very high frequencies require small components.