R 100 kΩ and C 10 µF
- Input
- R=100k, C=10u
- Expected output
- 1,099 s
About 1.1 x R x C, as in the datasheet.
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555 monostable pulse calculator
In monostable mode, a negative pulse on pin 2 triggers the output, which goes high for a time set by R and C. Pick the Monostable mode, type the two values and the duration appears. For the reverse path, enter the time and the resistor series.
About 1.1 x R x C, as in the datasheet.
One tenth of the previous case, with R ten times smaller.
Same RC product, same time, but with a very high resistor.
A timer of a few seconds.
2.1% error relative to the target.
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.
A negative pulse on pin 2 (TRIG) that drops below about one third of the supply. The output goes high and stays there until the capacitor reaches two thirds of the supply at the threshold, ending the cycle.
The capacitor rises from zero to two thirds of the supply, and that takes RC x ln 3, which is 1.0986 RC. The datasheet rounds it to 1.1. A full time constant, 1 x RC, would reach only 63% of the supply.
Down to a minimum of 10 µs, according to the TI datasheet. Below that, comparator storage dominates and the real pulse stops following the formula. For shorter pulses, use another circuit.
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%.
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