This write-up explains the Schmitt-trigger inverter oscillator using the 74HC14 (hex Schmitt-trigger inverter), gives the formulas for frequency and duty cycle, shows design steps, and provides example calculations and practical notes.
The 74HC14 oscillator is a robust and forgiving circuit. While online calculators provide quick answers, remembering the simplified formula is often faster for on-the-fly prototyping. When precision is required, always consult the specific manufacturer's datasheet for the hysteresis ($V_T+/V_T-$) values and use the full logarithmic formula. 74hc14 oscillator calculator