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Nebra Cell Modem Setup and Config

Meshtastic Pi

Nebra Cell Modem

After picking up a couple Nebra units, I read the manuals and specs sheets. And noticed the official optional cell modem. The original MSRP was insanely high but now is on eBay for $20. The model is the Quectel EG25-G Mini PCIe 4G Mobile Broadband Card w/ Antennas.

The kit comes with:

  • Quectel EG25-G Mini PCIe card
  • 2x LTE antenna
  • 2x ipex to N bulkhead

CAD model is available here.

Bands are:

  • LTE-FDD B1, B2, B3, B4, B5, B7, B8, B12, B13, B18, B19, B20, B25, B26, B28
  • LTE-TDD B38, B39, B40, B41
  • WCDMA B1, B2, B4, B5, B6, B8, B19
  • GSM 850, 900, 1800, 1900 MHz

Uses 3x IPEX-1 connectors : LTE main antenna + LTE diversity antenna + GNSS antenna)

It can do LTE, UMTS/HSPA+, and GSM/GPRS/EDGE. It can do MIMO for 150Mbps down and 50Mbps up. It uses multi-constellation Qualcomm IZat GNSS Gen8C Lite that supports GPS, GLONASS, BDS, Galileo and QZSS. SMS supports MT, MO, CB, Text, PDU. It can do voice calls, which has interesting possibilities.

Hardware Install

  • Insert SIM card - you’ll need it even just for GPS to work reliably. I don’t think it even needs to have service
  • Remove metal clip closer to the edge of the system board
  • Slide in the Mini PCIe at 30-45 degrees into the connector side
  • Press down to flat, there are two spring loaded clips that will hold it in position
  • Connect MAIN and GNSS ipex bulkheads and antennas. Leave DIV empty.

I recommend MAIN be on the opposite side of the enclosure from your 915MHz antenna for meshtastic. GNSS is passive so won’t interfere, I put that besides the main meshtastic antenna.

GPS works absolutely fine off the included LTE antenna. I’m connecting to 10-12 GPS sats indoors. If you need hyper accurate time, get an active GPS antenna.

Setup

This is brand new and I’m still working through the config. Please reach out if you run into any issues.


# install nmcli tools and everything else that'll be needed
sudo apt update
sudo apt install network-manager modemmanager gpsd gpsd-clients chrony socat

sudo systemctl enable NetworkManager
sudo systemctl start NetworkManager

sudo systemctl enable ModemManager
sudo systemctl start ModemManager

# list devices
nmcli device

# list status
mmcli -L
# look for /org/freedesktop/ModemManager1/Modem/0 [QUECTEL INCORPORATED] EG25

# If modem is 0 use -m 0 for everything, if 1 change to -m 1
sudo mmcli -m 0 --enable

# Activate cell modem without data
sudo nmcli connection add type gsm ifname "*" con-name mycell
# If you actually want to use the data, use:
# sudo nmcli connection add type gsm ifname "*" con-name mycell gsm.apn <your_carrier_apn>
sudo nmcli connection up mycell
sudo nmcli connection modify mycell connection.autoconnect yes


# run to ID ports
mmcli -m 0 
# output should be: ports: cdc-wdm0 (qmi), ttyUSB0 (qcdm), ttyUSB1 (gps), ttyUSB2 (at), ttyUSB3 (at), wwan0 (net)
# Note which one is (gps)

# Enable GPS
#
# DO NOT USE ANY OTHER GPS MODES! 
# gps-unmanaged lets you use gpsd, enabling any other gps modes (nmea) makes modemmanager take control of the GPS feed
#
sudo mmcli -m 0 --location-enable-gps-unmanaged
sudo mmcli -m 0 --location-set-enable-signal
sudo mmcli -m 0 --location-get
mmcli -m 0 --location-status


# sudo nano /etc/default/gpsd
#
# change /dev/ttyUSB1 to whatever port above uses (gps)
sudo tee /etc/default/gpsd > /dev/null <<'EOF'
START_DAEMON="true"
GPSD_OPTIONS="-n"
DEVICES="/dev/ttyUSB1"
USBAUTO="false"
# Socket-activated service will start gpsd when a client connects.
EOF

# Turn on gpsd
sudo systemctl enable --now gpsd
sudo systemctl start gpsd


#
# Connecting gpsd to meshtastic
#
# Meshtastic only seems to support SerialPath. I went with PTY rather than FIFO so that it can pass traffic via TTY.

# PTY creator
sudo tee /etc/systemd/system/meshtastic-pty.service > /dev/null <<'EOF'
[Unit]
Description=Meshtastic virtual PTY pair for GPS (socat)
After=network.target

[Service]
Type=simple
RuntimeDirectory=meshtastic
# Create two PTYs with stable links and permissive mode (tighten later if desired)
ExecStart=/usr/bin/env socat -d -d pty,raw,echo=0,link=/run/meshtastic/gps_in,mode=666 pty,raw,echo=0,link=/run/meshtastic/gps_feed,mode=666
Restart=always
RestartSec=2

[Install]
WantedBy=multi-user.target
EOF

# GPS pipe feeder
sudo tee /etc/systemd/system/meshtastic-gpspipe.service > /dev/null <<'EOF'
[Unit]
Description=Feed NMEA from gpsd into Meshtastic PTY
Requires=meshtastic-pty.service gpsd.service
After=meshtastic-pty.service gpsd.service

[Service]
Type=simple
# Wait until the PTY appears and is a char device; then stream raw NMEA
ExecStart=/bin/sh -lc 'while [ ! -c /run/meshtastic/gps_feed ]; do sleep 0.5; done; exec /usr/bin/env gpspipe -r > /run/meshtastic/gps_feed'
Restart=always
RestartSec=2

[Install]
WantedBy=multi-user.target
EOF

#
# End of services setup
#

# Enable and startup the meshtastic GPS services
sudo systemctl daemon-reload
sudo systemctl enable --now meshtastic-pty.service
sudo systemctl enable --now meshtastic-gpspipe.service
sudo systemctl start --now meshtastic-pty.service
sudo systemctl start --now meshtastic-gpspipe.service
systemctl --no-pager status meshtastic-pty meshtastic-gpspipe

# troubleshooting - you should see gps_feed and gps_in 
ls -l /run/meshtastic

# check for gps data - you should see a stream of NMEA traffic
sudo timeout 3 cat /run/meshtastic/gps_in

# Log check - make sure no errors
journalctl -u meshtastic-pty -b --no-pager

# point meshtasticd at the new serial feed
sudo nano /etc/meshtasticd/config.yaml

# Change /dev/ttyS0 to /run/meshtastic/gps_in , be careful of the spacing. YAML is sensitive about it. 
# Example:
#GPS:
#  SerialPath: /run/meshtastic/gps_in

#
# Meshtastic gps done 
#


# Connect GPS to system timeout
sudo nano /etc/chrony/chrony.conf
# add to end:
## GPS via gpsd
#refclock SHM 0 offset 0.5 delay 0.2 refid GPS poll 4

# Turn on the service 
sudo systemctl enable --now gpsd-time.service
sudo systemctl start --now gpsd-time.service
systemctl status gpsd-time.service --no-pager
sudo systemctl restart chrony
sudo systemctl restart gpsd

# Troubleshooting
#
# Run this and make sure it's filled with tons of updating numbers
cgps -s
# Check and see if you're getting GPS time data
chronyc sources -v

PPS?

Allegedly Quectel EG25-G does partially support PPS, which allows really accurate time keeping. We’d need to connect a wire from one of the pins on the card to one of the GPIO pins. This would bring down time inaccuracy to a few ms. But I haven’t poked at it yet.

Alternative setup

https://www.waveshare.com/wiki/EG25-G_mPCIe#How_to_Install_and_Use_Dial-up_Tool_.28Required_for_module_usage.29

Waveshare has an install script you can go with. I haven’t tried it out yet.

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