555 Timer Multivibrator Calculator
Calculate Astable and Monostable circuit values for the NE555 timer. Features dynamic SVG diagrams and suggests standard E12/E24 components.
Freq-
Period-
Duty Cycle-
About
The NE555 timer is the workhorse of timing circuits, capable of operating in Astable (continuous oscillation) or Monostable (one-shot) modes. Precise component selection is required to set the desired Frequency and Duty Cycle.
This tool solves the charging and discharging equations for the external capacitor C through resistors R1 and R2. Unlike theoretical calculators, this tool references standard component values to ensure your design can actually be built using E12/E24 series parts.
555 timer
electronics
pwm
frequency
circuit design
Formulas
Astable Mode:
f = 1.44(R1 + 2R2) C
Duty Cycle:
D = R1 + R2R1 + 2R2
Reference Data
| Capacitor Code | Value | Common Usage |
|---|---|---|
| 102 | 1 nF | High Freq / Debounce |
| 103 | 10 nF | Audio Freq |
| 104 | 100 nF | Standard Timing |
| 105 | 1 µF | Slow Pulses |
| 475 | 4.7 µF | Long Delays |
Frequently Asked Questions
In standard Astable configuration, the capacitor charges through R1+R2 but discharges only through R2. Since R1 cannot be zero, charge time is always longer than discharge time, meaning Duty Cycle > 50%. You need a bypass diode across R2 to achieve < 50%.
If R1 is less than 1k Ohm, excessive current flows into the Discharge pin (Pin 7) when the internal transistor is ON, potentially destroying the timer.