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I would like to make the serial work via GPIO. I have a gps module connected to these UART TX / RX pins and when I try to see the file /dev/ttyS0 it is not found
Your question is more Linux/RPi related. You need to find a tutorial on how to activate and use the UART on RPi in general (something like enable_uart in config.txt). AFAIK, the serial ports are "serial0", "serial1" and so on.