555 timer calculator
Get a 555's frequency and its high and low time, or the length of a single pulse, from its resistors and capacitor.
6.87 Hz
- Frequency
- 6.87 Hz
- Period
- 146 ms
- High time
- 76.2 ms
- Low time
- 69.3 ms
- Duty cycle
- 52.4%
The formulas
| To find | Formula |
|---|---|
| High time | t1 = 0,693 × (R1 + R2) × C |
| Low time | t2 = 0,693 × R2 × C |
| Frequency | f = 1,44 ÷ ((R1 + 2 × R2) × C) |
| One pulse | t = 1,1 × R1 × C |
How a 555 works
In the astable circuit the capacitor charges through R1 and R2 and discharges through R2 into pin 7; the output (pin 3) is HIGH while it charges and LOW while it discharges. So the high time is always longer than the low time and the duty cycle stays above 50%; for a shorter high, a diode goes across R2. To blink an LED once a second, R1 = 1 kΩ, R2 = 68 kΩ and C = 10 µF: about 1 Hz. The monostable circuit keeps its output on for a set time after a button press, like a timed light.
In the app, tick off every wire, match the parts to your inventory and pick up where you left off.
