Enter the following command
cat /dev/ttyUSB2&
echo -e "AT+CSQ\r\n" > /dev/ttyUSB2
If successful, the following will be displayed
If the following error occurs
It should be that the Raspberry Pi 4B has started the network service to manage 4G, so it cannot be opened.
Solution: You need to know the name of your network management service. My Raspberry Pi 4B is Networkmanager
Use sudo systemctl disable Networkmanager, then restart the Raspberry Pi 4B, and then use the initial command
Attach a command to return the corresponding meaning of the two data (the picture comes from the download area | Quectel AT Command Manual )
