PaulRB: I have to admit that you are absolutely right: I am absolutely newbie. But sometime has to be the first. I have referred to a relay module, like this:
From what you tell me, I learn, and I thank you for your words. In fact, I have proposed this challenge to stumble and, stumbling, learn. I put relays because it was what I knew. Yes I had read about the MOSFET but nowhere with the concretion that you have expressed: thank you. In a future project I will use the MOSFETs that you indicate to me.
Nowhere else on the Internet have I learned as much as I am learning here. I have to thank you.
Jobi-Wan: I have powered the relays with a 5V separate Arduino source. But that is not the problem for now: now, my problem is to be able to transmit to the 595 what the 165 command. I can do it with LEDs and resistors, no problem.
I know other programming languages but Arduino is new to me and, like all languages, has its peculiarities. What I do not master are the characteristic commands of this language. The rest, I'm familiar.
Tomorrow I will continue thinking about how to transmit the orders from 165 to 595. I do not think it is difficult. I think the most difficult thing, I've already done it. Or, better said, thanks to you, Jobi-Wan.