555 timer frequency calculator
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Inputs (astable mode)
Results
Frequency (f)
f = 1.44 / ((R1 + 2R2) × C)
480 Hz
Period (T)
T = 1 / f
2.08 ms
Duty cycle (D)
D = (R1 + R2) / (R1 + 2R2)
66.7 %
High time (t_high)
t_high = 0.693 × (R1 + R2) × C
1.39 ms
Low time (t_low)
t_low = 0.693 × R2 × C
693 µs
R1 and R2 are the current values (10 kΩ and 10 kΩ), C is 100 nF. The astable model above assumes the classic 555 timing equations.
About the 555 astable circuit
In astable mode the 555 charges and discharges C through R1 and R2, producing a square wave. Charge goes through R1 + R2, discharge only through R2, so the output is high for longer than it is low — duty cycle always exceeds 50%.
Need parts for the build? Find NE555 and timer ICs or timing capacitors in our catalog.