any good site, where i may learn about NON INVERTING SCHMITT TRIGGERS???

 

I don't know the answer to your question, but there are some of us here who know a lot about Schmitt triggers. What do you need one for?

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Ron

 

This is one question I'm always about to ask but I'm always shy... in simple words, what is a schmidt trigger and what are the general uses for it?

 

if you install PYTHON and the GTK+GLADE libs I am working on a program atm

I have no spare time atm (a project at work getting into hardware testing and I am moving house).

This is in a usable state (be it a few maths bugs)
Hopefully within a month I will have it finsihed then I will package all the libs and runtime environement together into a single installer so you wouldn't have to isntall:

python, GTK,GLADE

Attached Images

comp-program.png (17.8 KB, 757 views)

Attached Files

comparator.zip (112.3 KB, 22 views)

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Nothing is impossible.
Once a problem is realised, the rest is just details

 

Schmitt trigger:

is a comparator-arrangement , transistor-arrangement, logic chip whose puropse is to clean up a slow-moving signal and/or a noisy signal into a fast,clean rising/falling edge usable signal

Take the logic chip 74HC14 hex inverting Schmitt-trigger package. If you have a noisy signal OR an analogue signal and you wnat to make sure that even with all that noise (or slow-changing analogue signal) you still get a valid digital signal change then a schmitt is used.

It is used to clean up a signal with lots-o-noise that if it was passed into a standard gate it would cause lots of logic transitions, the hystesis within the sChmitt trigger ensures a clean signal

say you want to detect when a signal crosses a threshold, the a schmitt trigger is used. However, without hysteresis if it cross the triggering threshold it is very likely it will re-cross it giving you lots-o-false edges.

__________________
Nothing is impossible.
Once a problem is realised, the rest is just details

 

Also, see the Wikipedia definition.
Below are some waveforms to illustrate what Styx is saying. Note that the buffer has no hysteresis, while the Schmitt trigger has (in this case) 2 volts of hysteresis.

Attached Images

	schmitt_sch.gif (4.0 KB, 747 views)
	schmitt_waves.gif (10.2 KB, 745 views)

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Ron

 

Got it, thanks! That's why one picture is worthy more than a thousand words..

Now I understood why schmidt triggers are good for debouncing switches.

 

Hi Guys

I understand that these schmitt triggers can come in ic packages. Like the hex inverting trigger. However on these chips how do you set the threshold? If i understand correctly these ic's only have one input and one output. Therefore i assume they threshholds must be pre set within the chip and cant be changed. Also how is the hysterisis set? is this internally configured aswel?

The comparator or transistor schmitt triggers are easier to understand as these are several components in different configurations. Most of the time with two inputs etc. The ic schmitt trigger like i said is just one input and one output????????

cheers guys

Andy

 

Yes, everything is set inside the IC - like any other IC really?, you don't generally have the option for changing components inside the IC on anything else, so why on a schmitt trigger?.

Schmitt triggers only have one input, regardless of being IC or not, if you're looking at comparators or opamps configured as schmitt triggers, then the inverting input will normally be grounded. But the classic schmitt trigger is a two transistor circuit, one input, one output.

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http://www.winpicprog.co.uk

 

Thanks nigel,

Just a thought, can the schmitt trigger be used as an anologue to digital converter then?

If the output is always going to be a square wave and the input can be whatever it likes?

cheers

Andy

 

Yes, but a really poor spec one :lol: as can any logic input as well, but a 1 bit A2D isn't really of much use.

__________________
PIC programmer software, and PIC Tutorials at:
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