Never seen anything about KNX here but maybeyou'll get lucky.What exactly are looking for ?
But I honestly thought that fig 1. in https://www.researchgate.net/figure/Measured-waveform-of-the-data-communication-protocol-for-KNX-TP1-bus_fig1_308966692 would be self-explanatory about the signal.
I was planning something like that, where analog IN would try to stay at 2,5V so 0 bit would drop it to 2,05V and so on. Is it enought to secure devices?
But broblem is that gnd might not be same level at arduino's gnd and Im asking can I just isolate them with big condensators (KNX is selv voltage, so its not dangerous, its just I dont want fry my arduino or computers bus
The waveform you posted doesn't have 5V signals so why are you assuming that half of the input signal wouldbe 2.5V ?Show me the input signal you are trying to convert that is 5V.
that signal drops 0,45V but it was -4-5V
Well, in that picture?ok, drop in signal is 6V, and that spike up is really hard to measure, network size matters on that. and I might not have that good scope. (that is not my image)