What is the 555 astable frequency formula?

f = 1.44 / ((R1 + 2·R2) × C), with the high and low times set by R1, R2 and C.

Can a 555 produce a 50% duty cycle?

The standard astable output is always above 50%. Add a diode across R2 (or use a different topology) to reach close to 50%.

t = 1.1 × R × C — a single pulse of that length each time the timer is triggered.

免费555 定时器计算器，输入值直接在您的设备上计算。

Mode

R1 (Ω)

R2 (Ω)

Unit

Choose astable (oscillator) or monostable (one-shot).
Enter R1, R2 (astable) or R (monostable) and C with its unit.
Click Calculate for frequency, period and duty cycle, or the output pulse width.

Astable mode (continuous square wave):

f = 1.44 / ((R1 + 2·R2) · C)

t_high = 0.693 · (R1 + R2) · C | t_low = 0.693 · R2 · C

Duty cycle = (R1 + R2) / (R1 + 2·R2). The standard 555 astable output is always above 50% duty; add a diode across R2 to get close to 50%.

Monostable mode (single pulse on trigger):

t = 1.1 · R · C

What is the 555 astable frequency formula?: f = 1.44 / ((R1 + 2·R2) × C), with the high and low times set by R1, R2 and C.
Can a 555 produce a 50% duty cycle?: The standard astable output is always above 50%. Add a diode across R2 (or use a different topology) to reach close to 50%.
What is the monostable pulse width?: t = 1.1 × R × C — a single pulse of that length each time the timer is triggered.