This question is about a circuit I want to use as a schmitt-trigger and is directly related to my previous question. I modified that and changed the output with suggestion of some users. Here is the circuit:
In brief, the goal of this circuit is to sharpen the incoming pulses which will have either 12V or 24V amplitude where Vcc will be same as the pulse amplitude.
But I still have five questions regarding this circuit and wanted to open as a new question not to bother and bombard the same users with several questions.
Here are my questions:
1-) I set the hysteresis around 1V. But to do that I modified R1. Do modifying R1 requires to modify R7 and R8 as well? In simulation I get the result I want but still I wonder if there must be a relation between R1 and R7 + R8.
2-) Is R2 necessary? What could be the reason for that?
3-) Why is C1 set to 1uF but not 100nF which is the typical value?
4-) ZD1 and ZD2 forms a surge protection. Is it better to let them stay there or move them right after C2, (between C2 and the inverting input)?
5-) In some examples I see speed up capacitors across R1 and R4. Do I need them in this case and what are they needed for?