The capacitor then discharges through the same resistor toward the LOW output voltage. When the capacitor voltage drops to cap V sub cap T minus end-sub , the output flips HIGH again, restarting the cycle. 2. Calculation Formula The frequency of oscillation ( ) is inversely proportional to the resistance ( ) and capacitance (
R │ └───┐ │ Inv1 ─┼──► Inv2 ──► Output (clean square) │ C │ GND
The 74HC14 oscillator is a fundamental building block utilized across various circuit designs:
The Ultimate 74HC14 Oscillator Calculator Guide: Design & Principles 74hc14 oscillator calculator
To build a highly accurate or adjustable circuit, it is best practice to use a fixed resistor in series with a potentiometer. This allows you to manually tune the oscillator to your exact target frequency using an oscilloscope or frequency counter.
tlow=R⋅C⋅ln(VT+VT−)t sub l o w end-sub equals cap R center dot cap C center dot l n open paren the fraction with numerator cap V sub cap T plus end-sub and denominator cap V sub cap T minus end-sub end-fraction close paren The Total Period ( ) and Frequency (
To build a 74HC14 relaxation oscillator , the frequency is determined by a single resistor ( ) and capacitor ( ). Because the 74HC14 is an inverting Schmitt trigger The capacitor then discharges through the same resistor
+---[Ra]---+ | | D1 | +---[Rb]---+---C | | Inv1 out Inv1 in
f is approximately equal to the fraction with numerator 1.2 and denominator cap R center dot cap C end-fraction (Note: Using
Here is a quick reference table to get you started with common component values: Calculation Formula The frequency of oscillation ( )
For the most common configuration (single inverter, feedback resistor + capacitor to input):
Calculating the exact frequency of a 74HC14 oscillator is trickier than standard timers like the 555. The frequency depends directly on the internal threshold voltages ( VT+cap V sub cap T plus end-sub VT−cap V sub cap T minus end-sub ), which vary slightly based on your supply voltage ( VCCcap V sub cap C cap C end-sub