Calculadora do Timer 555

Temporização monoestável e astável

Operating Mode

Required Parameters

Resistor R1

Ohm

Resistor R2

Ohm

Timing capacitor C

Waiting for input data...

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Quick Answer

The 555 timer IC generates precise time delays (monostable: T = 1.1 x R x C) or continuous square waves (astable: f = 1.44 / ((R1 + 2xR2) x C)).

Documentation

555 Timer Astable Calculator

Design an NE555 / TLC555 astable oscillator. Enter R1, R2, and C to get frequency, period, high/low times, and duty cycle.

Quick start: R1 = 1 kΩ, R2 = 6.8 kΩ, C = 100 nF → about 986 Hz at 53% duty. This page is astable only.

555 astable frequency formula

f = 1.44 / ((R1 + 2×R2) × C)

T_high = 0.693 × (R1 + R2) × C

T_low = 0.693 × R2 × C

Duty = (R1 + R2) / (R1 + 2×R2)

Symbol	Pin / meaning
R1	VCC → pin 7 (discharge)
R2	pin 7 → pins 6/2 (threshold / trigger)
C	pins 6/2 → GND

Period T = 0.693 × (R1 + 2 R2) × C. Frequency is 1 / T, which is the 1.44 form above.

Why duty cycle is always over 50%

The capacitor charges through R1+R2 and discharges only through R2. Duty is therefore (R1+R2)/(R1+2 R2) — always above 50% on a standard bipolar 555.

Make R1 ≪ R2 to approach 50% (R1 = 1 kΩ, R2 = 100 kΩ → 50.5%)
Or add a diode across R2 (cathode toward pin 7) so charge bypasses R2
CMOS TLC555 / LMC555 can do true 50% with output feedback

Worked example — 1 kHz square wave

Choose C = 100 nF
R1 = 1 kΩ, R2 = 6.8 kΩ
f = 1.44 / ((1k + 2×6.8k) × 100n) = 986 Hz
Duty = (1k + 6.8k) / (1k + 13.6k) = 53.4%

Need a one-shot pulse instead? Open the full 555 Timer Calculator and switch to monostable (T = 1.1 RC).

Component ranges

Parameter	Recommended range	Notes
R1, R2	1 kΩ – 10 MΩ	Below 1 kΩ draws excess current
C (timing)	100 pF – 1000 µF	Film or C0G; avoid electrolytics
C (pin 5)	10–100 nF	Always bypass Control to GND
VCC	4.5 V – 16 V	Standard NE555 range

NE555 vs TLC555

Bipolar NE555 / LM555 draw a few mA and top out near 500 kHz. CMOS TLC555 / LMC555 draw microamps and run to about 2 MHz. The astable formulas are the same if the thresholds stay at 1/3 and 2/3 VCC.

Related tools

555 Timer Calculator — astable and monostable
RC Time Constant Calculator — τ = RC charging
Frequency to Period Converter — f ↔ T
RC Filter Calculator — timing-network cutoff
LED Resistor Calculator — blinker current limit

Design Notes

The NE555 works from 4.5V to 16V and can source/sink up to 200 mA. For low-power use, the CMOS TLC555/ICM7555 draws only 60-250 uA vs 3-10 mA for the bipolar NE555. The standard astable duty cycle is always greater than 50 percent because the cap charges through (R1+R2) but discharges only through R2. Add a diode across R2 for 50 percent duty cycle.

Common Mistakes

1
Forgetting the 0.01uF bypass capacitor on pin 5 (Control Voltage), causing erratic timing from noise.
2
Using electrolytic capacitors for timing: their 20 percent tolerance and leakage make timing inaccurate. Use ceramic or film caps.
3
Exceeding the bipolar NE555 max frequency (~500 kHz). Use the CMOS TLC555 for up to 2 MHz.
4
In monostable mode, the trigger pulse (pin 2) must be shorter than the output pulse and drop below 1/3 Vcc.

Engineering Handbox

1. T_high = 0.693 x (R1+R2) x C = 0.693 x 57k x 100nF = 3.95 ms 2. T_low = 0.693 x R2 x C = 0.693 x 47k x 100nF = 3.26 ms 3. Period T = 7.21 ms, f = 138.7 Hz 4. Duty Cycle = 57k/104k x 100 = 54.8 percent

VerificationOutput: 138.7 Hz square wave with 54.8 percent duty cycle.

Knowledge Base

Diferença entre astável e monoestável?

Astável: onda quadrada contínua (oscilador). Monoestável: pulso único quando acionado.

Fórmula monoestável?

Largura de pulso T = 1,1 × R × C. A constante 1,1 = ln(3).

Fórmula de frequência astável?

f = 1,44/((R1+2×R2)×C). Tempo HIGH = 0,693×(R1+R2)×C.

Para que serve o capacitor no pino 5?

Filtra ruído que causa jitter. Omiti-lo é o erro mais comum em projetos com 555.

Frequência máxima do 555?

NE555 bipolar: ~500 kHz. TLC555 CMOS: até 2 MHz.

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