Theoretical question: I have seen in many analog signal circuits that the analog input pin is pulled down through a resistance. Sometimes it is also pulled up and sometimes there is a capacitor involved.
What is the purpose of doing this?
What decides the value of the resistance and the capacitance?
Sample circuits below
(editing in vital information from comments)
I am confused of the role of R3 in first schematic, and C2 in second schematic. Second schematic also has a LED X1 while I assume TP6 is analog input, what role could the LED X1 be playing, these LEDs are generally more than just a pretty addition and their resistances have a role to play.
(/editing in vital information from comments)