The oscillation frequency ( ) for a 74HC14 Schmitt trigger relaxation oscillator is approximately determined by the formula:
If we express thresholds as fractions of Vcc (Vth+ = αVcc, Vth− = βVcc): tch = R·C · ln[(1 − β)/(1 − α)] tdis = R·C · ln(α/β) T = R·C · [ln((1 − β)/(1 − α)) + ln(α/β)] T = R·C · ln[ (α(1 − β)) / (β(1 − α)) ] f = 1 / (R·C · ln[ (α(1 − β)) / (β(1 − α)) ]) 74hc14 oscillator calculator full
| R | C | 1.2/(R×C) | Notes | |---------|---------|-----------|---------------------------| | 10 kΩ | 100 nF | 1.2 kHz | Audible range | | 100 kΩ | 100 nF | 120 Hz | Low freq, LED blinking | | 10 kΩ | 10 nF | 12 kHz | Audio/mid-range | | 1 MΩ | 1 nF | 1.2 kHz | Large R, small C | | 1 kΩ | 1 nF | 1.2 MHz | Max practical for 74HC14 | The oscillation frequency ( ) for a 74HC14
$$R \approx \frac0.8f \times C$$
Add a column for nearest E12/E24 component values, and you have your own custom calculator. Maximum Resistance: Do not go above 1MΩ (or
The 74HC14 is a hex Schmitt-trigger inverter (six independent inverters with Schmitt-trigger inputs). It’s commonly used to build simple, reliable oscillators—especially relaxation oscillators—because its Schmitt inputs provide clean switching with hysteresis, making oscillators tolerant to noisy or slowly changing signals. This guide covers principles, design equations, calculator-style worked examples, component selection, practical tips, and troubleshooting.