To build a 74HC14 relaxation oscillator , the frequency is determined by a single resistor ( ) and capacitor ( ). Because the 74HC14 is an inverting Schmitt trigger

He swapped the resistor for $2.2\textk\Omega$. Clipped. Now it was oscillating at $3.5\textkHz$. Too high.

  • Result: Use an $80\textk\Omega$ resistor (or a $100\textk\Omega$ potentiometer to tune it exactly).

    • Accurate for Low-Frequency Designs
    Matches the standard formula ( f = \frac1RC ) (with a correction factor ~0.55–0.7 depending on hysteresis thresholds). Many calculators include an empirical factor for the 74HC14.

    The "hysteresis" is the difference between these two points (

    2. The High-Frequency Limit ( > 1 MHz )

    As frequency increases, the internal propagation delay of the 74HC14 ($\approx 10-20$ ns) becomes significant. The simple $1/(0.55RC)$ formula fails. For 2-10 MHz:

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