SIM820X RNDIS Dial-Up

• Check whether SIM820X and Raspberry Pi and other devices are connected well through the following commands, if there is no problem, you can see Qualcomm devices and ttyUSB0-USB4

 lsusb
 ls /dev

• Open the ttyUSB2 port through minicom:

ls /dev/ttyUSB*
sudo apt-get install minicom
sudo minicom -D /dev/ttyUSB2

• Send the following command through minicom, and then wait for the module to restart

at+cusbcfg=usbid,1e0e,9011

• After dialing, the Raspberry Pi can see that usb0 gets the ip through the following command:

ifconfig -a

• Test usb0 networking status

 ping -I usb0 www.baidu.com

• If you cannot get the IP or fail to connect to the Internet, use the following commands to get the IP and connect to the Internet:

sudo dhclient -v usb0
sudo apt-get install udhcpc
sudo udhcpc -i usb0
sudo route add -net 0.0.0.0 usb0

Question:Why doesn't the NET indicator blink and I can't access the Internet after powering up for a while?

 Answer:

This situation may indicate a failure to successfully connect to the network. You can follow the steps below to troubleshoot:
1. First, confirm hardware issues:

• Check if the inserted SIM card can make calls and access the internet normally on devices such as mobile phones. It's recommended to test with SIM cards from multiple operators to rule out frequency band issues.
• Verify if the antenna is properly connected.
• Check the status of the NET indicator; if it's blinking or constantly on, it indicates a failure to register on the network.

2. Once the hardware is confirmed to be functioning properly, you can proceed with the following commands (AT commands) to further assess the network situation:

View firmware version information:
AT+SIMCOMATI
*Check that the SIM card is making good contact:
AT+CPIN?
*Turn the RF on (turn off flight mode):
AT+CFUN=1
*Check that the network mode is set to auto-seek:
AT+CNMP=2
*Check the signal quality of the current environment:
AT+CSQ
*Check if you have successfully registered to the network:
AT+CGREG?
*Check networking:
AT+CPSI?
*Check if the APN corresponds to the operator of the SIM card:
AT+CGDCONT?
*Check operator access:
AT+COPS?

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