SergeModular

OK, so I'm curious: what is this one useful for? What does it do that a
regular comparator couldn't?
Could it possibly give you an attack/decay envelope if you feed it a
gate?
Ignorant minds want to know.........

Hi

I'd wondered about this. Here's a link that
gives an answer - plus diagrams




http://hyperphysics.phy-astr.gsu.edu/Hbase/Electronic/schmitt.html

The Schmitt Trigger

The Schmitt trigger is a comparator application which switches the output negative when the input passes upward through a positive reference voltage. It then uses negative feedback to prevent switching back to the other state until the input passes through a lower threshold voltage, thus stabilizing the switching against rapid triggering by noise as it passes the trigger point.

greets

bill obrecht



-----Original Message-----

this guy's page is very good.
http://www.play-hookey.com/digital/experiments/rtl_schmitt.html

I've also read that you could use several of these with other logic to generate
extremely primitive cellular automata, or some such artificial intelligence(?)

i get really good pwm out of the Dual Schmitt Triggers, too! their proximity to my Preamp Detector makes them good trigger extractors, for example.

here's a good excerpt from the page

The key point to note here, however, is that the two threshold voltages are not the same. Rather, there is a gap between the two, where the positive-going and negative-going ranges overlap. This overlap denotes a property called hysteresis, and it is this property that makes the Schmitt Trigger so useful.

As you observed, even when you were very slowly and carefully adjusting the input voltage to this circuit, the output switching action was sudden and rapid. This is due specifically to the existence of the hysteresis in the circuit. In essence, the positive feedback in the Schmitt Trigger circuit serves to accelerate the transition from one state to the other, no matter how slow the rise or fall time of the incoming signal. Thus, the Schmitt Trigger serves to "square up" waveforms that have become malformed for some reason, such as extra capacitance in the circuit. It can also take an analog signal such as a sine wave or triangle wave and form it into a digital signal at the same frequency. This is most useful in instruments such as frequency counters, where we can measure the actual frequency of a signal.

Thus, the Schmitt Trigger is a very important circuit in digital electronics.