Quick Schmitt Trigger

Thread Starter

nDever

Joined Jan 13, 2011
153
Greetings Fellow Members,

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

Thread Starter

nDever

Joined Jan 13, 2011
153
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.


 

Attachments

Thread Starter

nDever

Joined Jan 13, 2011
153
Your last post makes no sense.
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



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.
 

Attachments

Ron H

Joined Apr 14, 2005
7,063
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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