Hi,
Well, thanks to confirm what I thought about the forum posts I read. My question for RS485 is a little bit different.
Regarding the EMC, I already tried what you suggested, the situation improved, but is still not acceptable. I inserted with a Raspberry with a brickd which is connected via Ethernet to the Laptop. Did not help. Maybe I'll try it with WLAN, but this is not an option for the demonstration. I also seperated it physically without the AC motor in the loop. This is the option that really helped, but there is still a reset if the motor is powering on orf off. Also a powered USB bridge was not chenaging the reset behaviour. I will also insert some shielding, the cases as well as the lines with proper shielding, not conenctied on both sides but only on one side. I think this will also improve the situation a little bit.
I did not try to disconnect the stepper supply, that might give a hint. One of the things I will try next as you suggested is a battery to de-couple supplies. But the very first thing I'll do is to apply an AC snubber filter, I got the delivery today.
I am looking forward that the AC-line snubber filter solves the problem, but if not my very last idea is the RS485 line. I orderer yesterday a Master Brick with RS485 Extension and it's on delivery today, so I think I'll get it on Monday, as it has not to cross the Atlantic :-)
KR,
Christof