In case of the CMOS(Complementary Metal Oxide Semiconductor) of the 74HC series, it is designed to use at the +5V supply voltage like other the 74 series TTL(Transistor Transistor Logic). The maximum supply voltage is +7V. The recommendation supply voltage is + 2V to +6V.
The upper limit of the oscillation frequency when using 74HC14 is about 20 MHz.
 Oscillation frequency
When making the value of the capacitor (C) is 1000 pF and the value of the resistor (R) is 22K-ohm, the oscillation frequency is as follows.
 The frequency by the calculation
| T | = | CR |
| = | 1000 x 10-12 x 22 x 103 |
| = | 22 x 10-6 (sec) |
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| f | = | 1/T |
| = | 45.5 KHz |
The measurement frequency
The oscillation frequency of the circuit which was made this time was 54.7 KHz. The power supply is +5 V.
This value is about 20% higher than the calculation. I think this difference according to the error of the parts.
Frequency change by the power supply voltage change
The graph on the left is the result which measured the change of the oscillation frequency when changing the power supply voltage.
The regulation is about 4 KHz/V.
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