Arduino + USB + Raspberry + MQTT

[jaraics]

Short version:

I need to connect two arduinos to a raspberry pi, over USB, and than have the raspberry act as a gateway over MQTT.
How can I do this? How can I connect the arduinos to the raspberry over USB? I could not find any option for the nodes to communicate with the gateway over USB.

(diagram of what I need to accomplish)
HomeAssistant <-MQTT-> Raspberry <- USB -> 2x Arduino <-GPIO> Switch

Long version:
I'm building a new house, and have every light switch wired to a central location (they are low voltage swithces, connected to the controller of the house, and I have separate controls that actually control the lights). Now there are more switches than GPIO pins on a raspberry, and I'm using two arduinos to connect all the switches.
I'm running HomeAssistant on a raspberry pi, and I'll be using that to keep track of the switch states, and turn on/off lights accordingly.
I thought I could use MySensors to read the GPIO pins on the arduino, and send updates to the raspberry, that would in turn publish those to an MQTT broker. But I can't seem to find any example that uses USB communication between an arduino node and a raspberry gateway.

Can someone help me?
Thanks!

[virtualmkr]

@jaraics MySensors supports multiple communication physics between the MySensors Gateway and the node Arduinos. Best supported are the wireless ones, but you can also use wires with RS485 (two wire) or the new added PJON driver which only needs one wire (plus ground).
One other option is to use only one Arduino with many IO pins like the Arduino Mega as a gateway arduino-mega-2560-rev3. This board has 54 IO pins. There are also cheap China clones available.

One issue for this way: I have never tried to use the Arduino Mega by myself.
Maybe someone else can give feedback to tell if a Mega will work as a gateway?

[OldSurferDude]

This post is deleted!

[OldSurferDude]

I've been using processing.org to capture data from Arduinos. I haven't tried with an RPi yet, but the link here is dedicated to just that.

Processing is more geared for doing really fancy graphics, but its ability to capture data and put it to a file is great, and, of course, send data to the Arduino.

I am inexperienced in interprocess communication, but, apparently processing can put the data out to MQTT check this link

Let me know how that works out for you!