Enter R_A and R_B in kΩ and C in µF. For example, 10,000 Ω is 10 kΩ, and 100 nF is 0.1 µF. Results show seconds, hertz and the percentage of each period that the output is high.
Accepted calculator bounds are 1–1000 kΩ for each resistor and 0.001–100 µF for the capacitor. These are input limits, not a guarantee that every combination is suitable for a physical circuit. Component tolerances, leakage and device behavior affect actual timing.
The two reference inputs have equal minimum and maximum values: leave them at their displayed values. Component entries are numerical magnitudes in the labeled units; the timing scale converts their product to seconds.
R_A connects the supply to DISCH; R_B connects DISCH to the joined TRIG/THRES timing node; C connects that node to ground. RESET remains inactive and CONT does not alter the thresholds. C charges through R_A + R_B and discharges through R_B, between approximately one-third and two-thirds of the supply voltage. This calculation excludes diode-modified circuits and the initial startup interval. See Texas Instruments, Astable Operation, section 6.3.2.
| R_A (kΩ) | R_B (kΩ) | C (µF) | High time (s) | Low time (s) | Period (s) | Frequency (Hz) | High-state duty (%) |
|---|---|---|---|---|---|---|---|
| 1 | 10 | 0.1 | 0.00076230 | 0.00069300 | 0.00145530 | 687.143544 | 52.3810 |
| 10 | 10 | 1 | 0.01386000 | 0.00693000 | 0.02079000 | 48.100048 | 66.6667 |
For R_A = 1 kΩ, R_B = 10 kΩ and C = 0.1 µF:
- High time = 0.000693 × (1 + 10) × 0.1 = 0.0007623 s.
- Low time = 0.000693 × 10 × 0.1 = 0.000693 s.
- Period = 0.0007623 + 0.000693 = 0.0014553 s.
- Frequency = 1 ÷ 0.0014553 ≈ 687.143544 Hz.
- High-state duty = 100 × 0.0007623 ÷ 0.0014553 ≈ 52.3810%.
Displayed results are rounded. An unavailable result indicates a calculation error, not a zero-valued time or frequency.
Can this topology produce exactly 50% high-state duty cycle?
For positive R_A and R_B, the formula gives a duty cycle above 50%. It approaches 50% as R_A becomes small relative to R_B. Setting R_A to zero is outside this calculator’s allowed inputs.
How are units handled?
Resistors and capacitance use numerical magnitudes in kΩ and µF, respectively. The fixed scale supplies the conversion to seconds. Dividing the fixed one-second reference by the period produces the numerical frequency in hertz. Keep the indicated entry units and fixed references unchanged.