Oscillating with the 74HC14

Posted by on Apr 9, 2011 in Blog, Etc | 6 Comments

Today, I built an oscillator with the 74HC14 hex inverter Schmitt trigger.
Here’s the datasheet.
I thought this was interesting, the inventor of the Schmitt trigger, Otto Herbert Schmitt (1913 – 1998), was a scientist who worked both in physics and biology. He figured out the trigger while studying neural impulse propagation in squid nerves.


I built this circuit with a capacitor 0.01uF and resistor 14.8k, which were just lying on the bench. I calculate a frequency of about 6.75kHz. Freq (Hz) = 1/ (R*F)

Which is pretty close to what shows on the oscilloscope … I’m looking at the output signal on pin 12.
Time (seconds) = 1/Frequency (Hz)

I then used all the gates available and made three oscillators. By using different values for R (Mohm range) and C (uF range) on each oscillator, and therefore creating three out of phase oscillators, I was able to get a nice color cycling effect on an RGB LED.


  1. lamin ceesay
    November 4, 2011

    very interesting little project. i just have a quick question on how u got your frequency.

    you stated freq = 1/(C*F)
    am guessing c = capacitor and F = resistor and * = multiplication yes/no . if yes then

    1/(0.01uF * 14.8K) = 1/(148^-6) = 6.75KHz

    please help me correct my way if am wrong. thanks

    • Sophi
      November 6, 2011

      Good catch- you are correct, and I have corrected the 2 typos.
      If you look at the oscilloscope, each square is 100us.
      You can see that a full cycle is just under a square and a half, say 150us.

      Frequency = 1/cycle = 1/(150*10^-6) = 6666.66Hz =6.7kHz

  2. ed
    August 27, 2014

    i understood the formula to be in this case: 1.2/(RC) and in that case it would be 8.1 kHz

    • fuqthegovt
      August 29, 2015

      It depends on the k factor, which in turn depends on the power voltage to the chip. It could be anywhere from 1.7 down to .8 within the datasheet limits of 2-6v (and the relationship isn’t linear at all). So if the supply varies by even a few mV (from a typical LM7805) your frequency will vary as well by a few parts per thousand (even when using 30-50 ppm RC components). This is why quartz crystal oscillators are used if you need a relatively stable frequency.

      • fuqthegovt
        August 29, 2015

        I guess I should also mention that temperature variations have an even bigger effect, close to 1% per C.

  3. Lee
    June 24, 2015

    So what does the input require to get it to oscillate?


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