I have Arduino UNO with expansion board where installed BL module and LED. But now I would like to send some info via USB to work with LED. I have such code for python:

I have been trying to send data to my Arduino Nano via a serial connection. The data is sent properly once I start sending data immediately after initialising. However, if there is a pause in sending data, it stops sending properly.

For a robotics project, I have to connect a Raspberry Pi together with two Arduino’s.
Each Arduino controls two stepper stepper motors.
The raspberry pi is sort of the “brain” for the project and thus needs to control the arudino’s actions, often multiple in a row. They communicate over the serial port, therefore in python I use the “pyserial” framework.
My problem is, that I can’t know when exactly an arduino has completed powering the stepper motor so I can run the next action. Often it is crucial for me to know when the Arduino is finished. What I need is the following:

I’m trying to connect from pc to arduino nano. I use python and pyserial library. Here is code: