Science & engineering
555 astable timer calculator
Estimate standard 555 timing, frequency and high-state duty cycle.
A clear answer. Here’s how.
For the standard two-resistor astable connection without bypass diodes, tHIGH≈ln(2)(RA+RB)C and tLOW≈ln(2)RB C. Frequency is 1/(tHIGH+tLOW); high duty cycle is (RA+RB)/(RA+2RB), always above 50% for positive RA. These are ideal threshold estimates; actual device, supply, leakage, tolerances and permitted component ranges require the selected datasheet.
See a worked example
Worked example
A fixed demonstration, separate from the values you enter above.
- Charging resistor RA (Ω)
- 1000
- Charging/discharging resistor RB (Ω)
- 10000
- Timing capacitance (µF)
- 10
Example result
- High-state time
- 0.0762461898616 s
- Low-state time
- 0.069314718056 s
- Period
- 0.145560907918 s
- Frequency
- 6.86997638519 Hz
- High-state duty cycle
- 52.380952381%