Re: Schmitt trigger....
ScorpFire,
The various Schmitt trigger buffers and inverters that are available have fixed hysteresis. The Schmitt trigger is a comparator that has positive feedback to provide its hysteresis (difference between the high and low reference levels). You can build a Schmitt trigger from a compator (or op amp) and provide the positive feedback through external resistors. In this manner, you can provide well defined high and low trigger levels.
,
Historical note; Originally, the term "Schmitt trigger" refered to a specific circuit using vacuum tubes (valves). Later the circuit was adapted to a specific circuit using transistors. Still later, the term "Schmitt trigger" was applied to any comparator circuit employing positive feedback for hysteresis.
Regards,
Kral