555 Timer Calculator

555 Timer Calculator

Example: 1kΩ for typical circuits
Example: 1kΩ for typical circuits
Example: 10μF for typical circuits

Results

Period:
Frequency:
Duty Cycle:
Time High:
Time Low:
Astable Mode Equations:
Frequency = 1.44 / ((R1 + 2R2) × C)
Duty Cycle = (R1 + R2) / (R1 + 2R2) × 100%
thigh = 0.693 × (R1 + R2) × C
tlow = 0.693 × R2 × C
555 Timer Modes Explained: Monostable vs Astable

Understanding 555 Timer Modes: Monostable vs Astable

Introduction to 555 Timer

The 555 timer IC is one of the most versatile integrated circuits in electronics. It can operate in two fundamental modes:

  • Monostable Mode (One-shot pulse generator)
  • Astable Mode (Free-running oscillator)

Monostable Mode

Characteristics

  • Generates single output pulse when triggered
  • Pulse duration determined by external RC components
  • Remains stable in one state until triggered
  • Common applications: Timers, push-button switches, bounce elimination

Key Formula

Time Delay (T) = 1.1 × R1 × C1

Astable Mode

Characteristics

  • Generates continuous square wave output
  • No stable state - oscillates between high and low
  • Frequency determined by two resistors and one capacitor
  • Common applications: LED flashers, clock generators, tone generation

Key Formulas

Frequency (f) = 1.44 / ((R1 + 2R2) × C)
Duty Cycle = (R1 + R2) / (R1 + 2R2) × 100%

Mode Comparison

Feature Monostable Astable
Output Type Single pulse Continuous square wave
Stable States One None
Components Required 1 Resistor, 1 Capacitor 2 Resistors, 1 Capacitor
Trigger Requirement External trigger needed Self-triggering

Using the 555 Timer Calculator

For Monostable Mode:

  1. Select "Monostable" mode
  2. Enter resistor (R1) value
  3. Enter capacitor (C1) value
  4. Get time delay calculation

For Astable Mode:

  1. Select "Astable" mode
  2. Enter both resistor values (R1 & R2)
  3. Enter capacitor (C1) value
  4. Get frequency and duty cycle

Component Selection Tips

  • Use ceramic capacitors for high frequency applications
  • Electrolytic capacitors for long time delays (>1 second)
  • Keep resistor values between 1kΩ and 10MΩ
  • Add decoupling capacitor (0.01μF) between VCC and GND