NE555 Timer Calculator with Waveform Simulation
Calculate R/C component values for the NE555 timer IC in astable (free-running oscillator) and monostable (one-shot) modes. Simulates the output and capacitor voltage waveforms.
Circuit Constants
- To increase frequency, decrease R or C.
- In astable mode, set R2 >> R1 to approach a 50% duty cycle.
Calculated Results
Timing Chart & Charge/Discharge Waveform
NE555 Timer IC Operating Modes
The NE555, designed in 1971, remains one of the most widely produced ICs in history. With only an external resistor and capacitor, its two internal comparators and an RS flip-flop produce precise switching clocks or timed pulses.
Astable Multivibrator (Free-Running)
The output continuously alternates between HIGH and LOW, generating a square wave. The capacitor charges and discharges between the internal reference thresholds of 1/3 Vcc and 2/3 Vcc.
- Charge path (Output HIGH): Current flows through R1 + R2 to charge C, so t_high = 0.693 × (R1 + R2) × C.
- Discharge path (Output LOW): The internal discharge transistor (pin 7) pulls C down through R2 to ground, so t_low = 0.693 × R2 × C.
Monostable Multivibrator (One-Shot)
The output stays LOW in its stable state. When a LOW trigger pulse is applied to pin 2, the output goes HIGH for a precisely timed interval (t = 1.1 × R1 × C) before latching back to LOW.