Quick Schmitt Trigger

Discussion in 'General Electronics Chat' started by nDever, Mar 4, 2011.

  1. nDever

    Thread Starter Active Member

    Jan 13, 2011
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    Greetings Fellow Members,

    Are there any common household devices that carry a Schmitt trigger? I need a circuit that can digitize my clock signals.
     
  2. Jaguarjoe

    Active Member

    Apr 7, 2010
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    Did you look at a CD4093?
     
  3. nDever

    Thread Starter Active Member

    Jan 13, 2011
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    I do not have any of those; only normal NAND gates.
     
  4. KMoffett

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    Dec 19, 2007
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  5. Wendy

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  6. nDever

    Thread Starter Active Member

    Jan 13, 2011
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    The original signal is as depicted in the attachment. It is based from this schematic. I built a Schmitt trigger from the attached schematic and achieved the corresponding signal. The high voltage threshold was about 2.5V and the low threshold was about 2.4V. I am not sure why the signal from the trigger looks this way.


    [​IMG]
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Your last post makes no sense to me.
     
    Last edited: Mar 5, 2011
  8. nDever

    Thread Starter Active Member

    Jan 13, 2011
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    I apologize for being unclear. I require a square wave with a peak voltage of about 4V (5V ideally) for a general clock driver for my Z80. I built a circuit from the schematic below

    [​IMG]

    and achieved a signal that looks like the signal in the first image attached. This signal would not serve as a good clock signal for a CPU because of the voltage spikes. I need to have a clean square wave signal and I have tried to debounce the signal by adding an RC circuit across the crystal but did not yield any better results. I then decided to try a Schmitt trigger to digitize my signal. I do not have any trigger ICs, so I decided to construct one from NPN transistors (the schematic for this circuit is the second attachment). When I applied the original signal to the trigger circuit, I received a signal that looks like the signal in the third image attached. As you can see, that is no square wave. This is a problem.
     
  9. Ron H

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    Apr 14, 2005
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    The signal from your oscillator cannot be cleaned up with a Schmitt trigger. The ringing you see is probably due either or both of the following:
    1. The ground lead on your scope probe is too long.
    2. You have no ground plane, or a very poor one.
    3. Your IC does not have a proper decoupling cap between Vcc and GND pins.

    The Schmitt trigger schematic you posted will not give TTL levels at the output, but, as I said, you don't need one. In fact, if you did pass the clock signal through a good, high speed Schmitt trigger (such as 74XX14), you would probably see almost exactly the same ringing and overshoot.
     
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