Q Light Controller+

Hi there,
I'm trying to do a little project to make some lights automatic using QLC+ Raspberry Pi latest image.
The thing is that i want to connect the arduino through USB to the RPi and use the Serial communication of the arduino to send some control data to QLC+ that i gather from sensors.
I've tried different options and i didn't succeed in any of them.

Has anyone did ths before or has some clue?

Thanks in advance

I do this with a relay module

Connect output pins of the Arduino to the relay module input logic (on the left of the image below)

Then connect they relay outputs from the 3.3v pin to a GPIO pin(s) on the Raspberry Pi (on the right in the image below) so... 3.3v output pin on the Pi to a relay output, then to a GPIO pin.

The Arduino operates at 5v and the Pi operates at 3.3v so this is an easy way to get the Arduino to trigger the Pi without worrying about that voltage difference and pullup/pulldown resistors.