RA 1 kΩ, RB 10 kΩ, C 1 µF
- Input
- RA=1k, RB=10k, C=1u
- Expected output
- 68,7 Hz
Period of 14.56 ms and a high duty cycle of 52.4%.
Carregando ferramenta… / Loading tool…
555 astable calculator
Fill in RA, RB and C with the unit of each and the frequency shows up at once, along with the period, the high time, the low time and both duty cycles. The same math applies to any 555 oscillator built with two resistors and one capacitor.
Period of 14.56 ms and a high duty cycle of 52.4%.
With RA equal to RB the high duty cycle is 66.7%.
High of 138.6 µs and low of 69.3 µs.
High duty cycle of 55.0%, close to 50%.
High of 138.6 ms and low of 69.3 ms.
Per the TI datasheet, f = 1 / T and T = 0.693 x (RA + 2RB) x C, giving f ≈ 1.44 / ((RA + 2RB) x C). With RA = 1 kΩ, RB = 10 kΩ and C = 1 µF, T is 14.56 ms and f is 68.7 Hz.
RA takes part in charging the capacitor and is the load on pin 7 while it discharges. The datasheet tests astable mode with RA between 1 kΩ and 100 kΩ, and the calculator warns below and above that. Very high values let capacitor leakage and threshold current matter.
No. Charging and discharging happen between 1/3 and 2/3 of the supply itself, so the frequency does not depend on it as long as it holds constant during the cycle. The NE555 operating range runs from 4.5 V to 16 V.
The math assumes ideal components. A wide-tolerance electrolytic capacitor, 5% resistors and capacitor leakage move the result. Enter the tolerances in Options to see the possible range, and measure with a frequency counter or oscilloscope.
With 5% on the resistors and 10% on the capacitor: frequency from 911.7 mHz to 1.232 Hz and high duty cycle from 50.3% to 50.4%.
Everything is calculated in your browser. No values are sent to servers.