IC 555 Timer Calculator
Ω
kΩ
MΩ
Ω
kΩ
MΩ
Ω
kΩ
MΩ
F
mF
µF
nF
pF
Astable Calculations
Frequency (f): –
Period (T): –
Duty Cycle: –
Time High (t1): –
Time Low (t2): –
Monostable Calculations
Pulse Width (Time Delay): –
Understanding the 555 Timer IC
The IC 555 timer is one of the most versatile and widely used integrated circuits in electronics. Developed in 1971, it functions as an oscillator, pulse generator, or timer. This calculator helps you determine the output frequency, duty cycle, and pulse widths based on your resistor and capacitor values.
Astable Mode (Free Running)
In astable mode, the 555 timer triggers itself and runs as an oscillator (a multivibrator). This generates a continuous square wave. It is commonly used for LEDs flashers, pulse-width modulation (PWM), and clock signals.
t1 (High) = 0.693 × (R1 + R2) × C
t2 (Low) = 0.693 × R2 × C
Frequency = 1.44 / ((R1 + 2 × R2) × C)
t2 (Low) = 0.693 × R2 × C
Frequency = 1.44 / ((R1 + 2 × R2) × C)
Monostable Mode (One-Shot)
In monostable mode, the 555 timer acts as a single pulse generator. When a trigger signal is received at Pin 2, the output goes High for a specific duration and then returns to Low until triggered again. This is ideal for timers, touch switches, and frequency dividers.
Pulse Width (t) = 1.1 × R × C
Practical Example
If you are building an LED blinker using Astable mode with R1 = 1kΩ, R2 = 100kΩ, and C = 10µF:
- Time High: 0.70 seconds
- Time Low: 0.69 seconds
- Frequency: 0.716 Hz (roughly one blink every 1.4 seconds)
- Duty Cycle: 50.2%
Component Selection Tips
For best results, avoid using very small resistor values (below 1kΩ) to prevent excessive current draw, and avoid very large values (above 10MΩ) where leakage current might interfere with timing accuracy. For the timing capacitor, tantalum or polyester capacitors are preferred over electrolytic ones for high-precision applications due to lower leakage and tighter tolerances.