Arduino uno not listening to raspberry pi 2?

Question

Python

I programmed the Arduino to perform actions when receiving a signal on the com port. When transmitting these signals from the computer, everything is fine. When connecting the Arduino to the raspberry pi 2 and transmitting these signals, the arduino flashes a light (received a signal), but no action. What can be the problem?
I send signals through the Serial library in python.
Raspbian axis.

Answer 1

How is it connected, arduina to raspberries? Via usb or via gpio ttl? Please note that raspberry ttl works at 3.3V, and duny ttl at 5.0V. In this case, the duna may simply not have enough voltage to a logical unit at the input, in which case a level converter must be used.

Answer 2

Most likely the port is not initialized properly. I recommend reading the article Arduino Host Client in C (Linux)