Setting up 4G Serial Modem (i.e. SIM7600X) via PPP

1. Dependencies

Install ppp

sudo apt install ppp

2. PPP Configuration

2A. Copy existing provider settings for ppp

cd ~/pyduino/sim7600/ppp/peers
sudo cp optusconnect /etc/ppp/peers/optusconnect

2B. Manual setup of ppp provider example

Copy an example provider file and naming it optusconnect for editing (Optional: switch to root permission sudo su)

sudo su
cd /etc/ppp/peers
cp provider optusconnect

Open optusconnect provider file for editing, use any prefered editor, i.e. nano instead of vim

sudo vim /etc/ppp/peers/optusconnect

Edit the following details Replace ******** with APN of provider i.e. connect for Optus

connect "/usr/sbin/chat -v -f /etc/chatscripts/pap -T ********"

to

connect "/usr/sbin/chat -v -f /etc/chatscripts/gprs -T connect"

Replace /dev/modem with serial port modem is connected to. Most likely /dev/ttyS0

Append the following to the file

# Accept new IP addresses from IPCP negotiations (default)
ipcp-accept-local
ipcp-accept-remote

# Do not ask the remote to authenticate.
noauth

# No hardware flow control on the serial link with GSM modem
nocrtscts

# No modem control lines with GSM modem
local

3. Testing the connection

Start connection

sudo pon optusconnect

To turn device serial connection off

sudo poff optusconnect

Can check syslog if connection was successfull tail -n 30 /var/log/syslog

Or check if the modem interface ppp0 appears in ifconfig

Now add the modem as a default route and try to ping a public IP or address (e.g. Google DNS)

NOTE: If connected via wifi, route add may terminate ssh connection as all traffic will be routed via 4G

Routes all traffic via ppp0 network interface

# Test connection via ppp0 interface
ping -I ppp0 8.8.8.8
ping -I ppp0 www.google.com
traceroute -i ppp0 www.google.com

# Only use following if ssh connection is not over wifi
sudo route add default dev ppp0
or
sudo route add -net 0.0.0.0 ppp0

ping 8.8.8.8
ping www.google.com
traceroute www.google.com

To remove

sudo route del default dev ppp0

Note: Routing information does not persist on reboot, continue reading to set it up

4. Setup automatic connection and network routing on boot

Note: If connection is turned off manually during session, need to reboot or follow previous "testing the connection" to set up routing info for current session

• Need to edit /etc/network/interfaces file

sudo vim /etc/network/interfaces

• Include the following before the line source-directory /etc/network/interfaces.d

# Load ppp0 optusconnect as an interface
auto optusconnect
iface optusconnect inet ppp
provider optusconnect

Example:

# interfaces(5) file used by ifup(8) and ifdown(8)

# Please note that this file is written to be used with dhcpcd
# For static IP, consult /etc/dhcpcd.conf and 'man dhcpcd.conf'

# Load ppp0 optusconnect as an interface
auto optusconnect
iface optusconnect inet ppp
provider optusconnect

# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d

5. Configuring modem to power on boot

PWR Modes by jumper settings

Modes	Description
3v3	Device power up on connection to power (No configuration needed)
D6	Control device using rpi GPIO (BCM-GPIO6, WPI-GPIO22)
No Jumper	Manual powering of device using PWRKEY button

ONLY PERFORM THE FOLLOWING if PWRKEY is shorted on device between PWR and D6 by jumper setting

Need to edit /etc/rc.local to trigger the power key

sudo vim /etc/rc.local

Add the following before the line Exit 0

5A. Using python

& at end of line is to fork the python process to allow boot sequence to continue, or else boot will hold until python script finish executing

• Without Logging

# Initialize SIM7600 on BCM-GPIO6, WPI-GPIO22
python /home/pi/sim7600.py &

• With logging, initializes a second bash process to execute script

# Initialize SIM7600 on BCM-GPIO6, WPI-GPIO22
sudo bash -c "python /home/pi/sim7600.py > /home/pi/sim7600.log 2>&1" &

5B. Using shell

Toggle rpi GPIO to send "power on" signal via PWR breakout pin, module remains on if already on

#TODO: Needs testing for validation
# Initialize module, BCM-GPIO6, wPI-gpio22
printf "Initialize SIM7600 Module"
if [ ! -e /sys/class/gpio/gpio6 ]; then
    sudo echo "6" > /sys/class/gpio/export
fi
sudo echo "out" > /sys/class/gpio/gpio6/direction
sleep 0.1
sudo echo "1" > /sys/class/gpio/gpio6/value
sleep 0.5 # Min time of 0.1sec and less than 2.5sec
sudo echo "0" > /sys/class/gpio/gpio6/value
sleep 0.1
sudo echo "6" > /sys/class/gpio/unexport

SIM7600 Python Utility Script Content

Located in ~/pyduino/sim7600 folder Default operation on launch of python script sim7600.py is to power on the module via GPIO

To power on module, uses gpio to toggle pwrkey

python sim7600.py

Reboot, uses AT commands to reboot modem

python sim7600.py reboot

Check status of module, uses AT command

python sim7600.py status

Opens a serial session to be able to send custom AT commands to 4G module

python sim7600.py serial

To power off module, uses gpio to toggle pwrkey

NOTE will actually toggle power, so if module is off will turn on module, DO NOT USE if device connection is soley over 4G network

python sim7600.py off