555 Timer IC — NE555 Circuit Modes

Real-time dual-trace oscilloscope showing capacitor voltage (V_C) and output (V_out). Thresholds at V_CC/3 and 2V_CC/3 shown as reference lines.

Timer Mode

Astable Components

R1 (charge) 10kΩ

1kΩ 100kΩ

R2 (discharge) 10kΩ

1kΩ 100kΩ

C (timing) 100nF

10nF 10000nF

Monostable Components

R (timing) 10kΩ

1kΩ 500kΩ

C (timing) 10000nF

100nF 100000nF

Bistable Controls

SET drives TRIG (pin 2) LOW → Q goes HIGH
RESET drives RST (pin 4) LOW → Q goes LOW

CURRENT OUTPUT Q

LOW

Supply Voltage

V_CC 5V

5V 15V

Live Readings

Frequency — Hz

Period — ms

t_HIGH — ms

t_LOW — ms

Duty Cycle —%

Astable Mode — Free-Running Square Wave

f = 1.44 / ((R1 + 2·R2)·C) | V_C oscillates between V_CC/3 ↔ 2V_CC/3

V_C cap

V_out

ACTIVE FORMULA


f = 1.44 / ((R1 + 2·R2)·C)   |   DC = (R1 + R2) / (R1 + 2·R2)


Charge τ = (R1+R2)·C   |   Discharge τ = R2·C   |   V_thresh = 2·V_CC/3 ≈ 3.33V

Circuit Diagram — NE555