I actually did not write or format anything. I just made connections directly, taking the single connection scheme of each component from tutorials, testing each circuit on a breadboard singularly, then all together always on the breadboard, then rewiring directly from Arduino Board to component. I'm not a professional electronic, I'm just an employee in freight forwarding with some electrician background doing some of this for fun and trying to give it a practical use. I would post it if someone helps me find a good way to do it, as I had already asked. I've checked circuito.io but I cannot modify the connections it suggests to reflect mines; I was checking fritzing but I've found people telling to stay away from it, and mostly it is pretty time consuming to redesign it all, and as told, I'm an employee doing my job all day long, so I have to find the time to do it. I will work on it on this weekend, even If I can't understand how this can help, being my issue not related to wrong connections, shorts or whatever.
Why i'm not posting my code: because it works fine, it worked fine for a LONG period before final installation of the project, and I made all the necessary tests before posting to exclude the fact that the issue is caused by the code. But it is surely an highly unoptimized code, so there is a very high risk that people would concentrate on the code losing sight of the real issue. Posting the code would only be a distraction
Why i'm not posting the photos of the project: You'd see a bundle of wires that wouldn't help. Project is partially torn down due to the disassembly of the relay part, buttons/LED resistors are bundled in tape so you can't see them, LCD is connected reversed on the box cover so you aren't seeing how it is connected, but mostly: the project has been working flawlessly for some days on my desk, while I was working on the sketch. The issue begun when I positioned the box on his final location, where I had it running fine until I attached the stove to the plug. I also made some tests before asking here, by restarting the project and checking how and when the issue happened. When the stove starts, no matter what the project is doing, the LCD gows in garbage mode. This is why I can say it not way related to functions, or miswiring, and this is why I posted on "General Electronics" and not in "Programming" or "Displays". And the fact that I was addressed to "shielding" and "grounding" or "try a capacitor here and here", and not "you have the wrong Pin 2 connected" or " Add a lcd.clear() here or here" tells me I made the correct choice.
You ask me a photo of the wall plug: It's a standard Gewiss multiplug wall box:
I worked as electrician, installing these in dozens. It is wired fine. It is mounted 1 mt far from the arduino box. Can you please explain me how the positioning or whatever can affect the behavior of the project (a part from the fact that, being the stove and the arduino on the same line, when the stove starts it causes a pitch leading to the problem?)
I'm trying to be as much as kind as possible, because I was admin in forums in the pasts so i know people is trying to help. So I'm replying even when I'm asked what relays I'm using even after I wrote at least twice that no relay is connected, and tried to make clear that I'm well aware of the relay issues when working with hi voltages
Call me arrogant if you want, but I made my homeworks .
This is why, frankly speaking, I'm a little frustrated by the fact you ask me to read the forum rules...
I will check the grounding of the whole circuit
I will try the capacitors on the LCD pins
failing these, I will try my franken-hack, unless someone tells me there is no way this is going to work
I WOULD try shielding, but as I already told, I'm not pretty sure on how this might be done to be effective
I will post the results, because as told, I used to run forums, and I've always hated people coming to ask for help, receiving some and never giving a feedback
If in the meanwhile someone have some more ideas on how this can be solved and/or suggests me the best way to write the diagram, I'd be glad to check those too.