555 Timer Astable Circuit Calculator
Output
Theory of Operation
The 555 timer in astable mode is a multivibrator circuit that oscillates between high and low states continuously, producing a square wave output. The frequency and duty cycle of this output waveform depend on the resistor and capacitor values in the circuit.
Frequency: f = 1.44 / ((R1 + 2 × R2) × C)
- R1: External resistor connected to the discharge pin (in Ohms).
- R2: External resistor connected to the threshold pin (in Ohms).
- C: Capacitor connected to the timing network (in Farads).
Duty Cycle: D = ((R1 + R2) / (R1 + 2 × R2)) × 100%
The high and low time durations of the output waveform are given by:
- Time High (TH): 0.693 × (R1 + R2) × C
- Time Low (TL): 0.693 × R2 × C
Applications
- Waveform Generators: Used to generate square waves for timing and control applications.
- PWM Circuits: Pulse width modulation for motor speed control.
- Flashing Lights: Ideal for creating blinking LEDs or other oscillatory circuits.
Example Calculations
Example 1: Basic Calculation
Given:
- Resistor R1 = 10kΩ (10,000 Ω)
- Resistor R2 = 100kΩ (100,000 Ω)
- Capacitor C = 10µF (0.00001 F)
Formula:
- f = 1.44 / ((R1 + 2 × R2) × C)
- D = ((R1 + R2) / (R1 + 2 × R2)) × 100%
Calculation:
- f = 1.44 / ((10,000 + 2 × 100,000) × 0.00001) = 0.69 Hz
- D = ((10,000 + 100,000) / (10,000 + 2 × 100,000)) × 100% = 35%
Result: Frequency is 0.69 Hz, and Duty Cycle is 35%.