i think i'm finally getting how it functions, it's not very accurate though. it seems the author used the 3rd lowest pin so as to allow for the propagation delay of the buffer circuit, through that, there's the hope that the buffer output would actually coincide with the signal's zero crossing...
i now have other challenges:
#1 how do i increase the frequency range, from 1khz? i believe the limitation to 1khz is to severe...
#2 surely one would want to measure other voltage levels as well other than 5v? i'm thinking of using a voltage divider (range selector sort of) at the signal input to increase the range we can measure, but the problem is that, that would always give me a decremated waveform on the screen, smaller than what i'm actually inputting...
any ideas?