How to make Arduino friends with 200 relays?

Question

Arduino

There is a need to assemble a relay control module, preferably on an Arduino. Is it possible to assemble some intermediate element that will control relays in the amount of 200 pieces. ?

Answer 1

You can use shift registers, but for each data input, the relays will turn off and on again for a second, plus the relays must be with their own power supply (and probably better with an optocoupler), since I think the arduino will not withstand 200 pcs.
(for the sake of interest, I just can’t imagine where 200 relays under the control of arduino might be needed, can you share?)

Answer 2

You have 200 (!) relays.
Well, why, why do you need Arduino ?!

Answer 3

Connect four Megas to each other (rx, tx), one will be the center one.