LoRaWAN Modbus Gateway

The Lobaro LoRaWAN Modbus Gateway is a LoRaWAN Gateway with integrated LoRaWAN Network Server providing sensor data via Modbus.

Hardware Components

LoRaWAN Gateway
IMST VersionRAK Version

Currently not available

  • LoRaWAN
  • Connectivity: LAN
  • Order number: 8000101

New Version based on RAK Wireless

  • LoRaWAN
  • Connectivity: LTE / LAN / WLAN
  • Order number: 8000202

USB-Modbus Adapter

Software Components

  • Chirpstack Network Server
    • Semtech Packet Forwarder
    • Chirpstack Gateway Bridge
    • Chirpstack Network Server
    • Chirpstack Application Server
    • Postgres
    • Redis
  • Lobaro Modbus Server

Usually you will not need to change anything inside the Chirpstack Application Server. All devices are managed by the Lobaro Modbus Server.

Remote access

Per default the gateway obtains the IP address via DHCP. If configured with a fixed IP address, the gateway has a label with the configured IP address and subnet.

SSH Access

The gateway can be accessed via SSH on port 22. Default login credentials are:

  • User: pi
  • Password: lobarogw
  • IP: DHCP with fallback to (IMST) or (RAK)
    • On RAK with latest image also possible via WLAN AP:
      • Default SSID "RAKMBG_XXYY" (XX and YY last bytes of WLAN adapter MAC) and password "lobarowireless", RAK IP

Management UI


SD Card write protection

Write protection on the SD card was removed in current firmware releases

To change any filed on the SD Card (including all config files) you need to execute the script:


To disable write access, restart the gateway or execute:


Lobaro Modbus Server

The Lobaro Modbus Server (lobaro-modbus-server) is responsible for fetching data from the local LoRaWAN Network Server and provides received data via modbus.

vim can be used to edit files.

To use WinSCP with the user "pi" the files need write access:

sudo chmod o+wr /etc/lobaro-modbus-server/lobaro-modbus-server.yml

Open or change configuration of the Lobaro Modbus Server:

sudo vim /etc/lobaro-modbus-server/lobaro-modbus-server.yml

After editing the configuration lobaro-modbus-server must be restarted:

sudo systemctl restart lobaro-modbus-server

Check the status with

sudo systemctl status lobaro-modbus-server

Check the logs with

sudo journalctl --no-pager -e -u lobaro-modbus-server


Beside checking the logs, you can also analyze the files in the dataDir (see config).

There are two files that help writing the config and checking the results.

  • device-data.json - contains raw json received from Chirpstack. Can be used to verify mapping[].register.value configuration.
  • register-map.json - contains all register values provided via modbus. All values are formatted as int.

Example device-data.json:

  "0000000000000000-1": {
    "adr": true,
    "applicationID": "1",
    "applicationName": "default",
    "data": "AAMEAOQN1g==",
    "devEUI": "0000000000000000",
    "deviceName": "0000000000000000",
    "fCnt": 1,
    "fPort": 1,
    "object": {
      "temp": 22.8,
      "vBat": 3.542,
      "version": "v0.3.4"
    "rxInfo": [
        "gatewayID": "0000000000000000",
        "loRaSNR": 8.8,
        "location": {
          "altitude": 0,
          "latitude": 0,
          "longitude": 0
        "name": "default",
        "rssi": -36,
        "uplinkID": "ce2e086a-d747-4813-9428-b7a4a45abcc8"
    "txInfo": {
      "dr": 0,
      "frequency": 868300000

Example register-map.json:

  "Register": {
    "100": {
      "Val": 0,
      "Type": 1,
      "UpdatedAt": "2020-02-07T13:44:03.39750918Z"

Configuration file

Register Types

For mapping.[device].register.type the following types are valid:

"type" ParameterRegister Count

Example Configuration
# The application stores persistent data at this path
dataDir: /mnt/ssd/var/data/lobaro-modbus-server/

# Chipstack configuration. Required to manage configured LoRaWAN devices.
  server: http://localhost:8080
  broker: localhost
  appId: 1
  username: admin
  password: admin

# Modbus configuration. 
# <v1.2.0: Serial mode is fixed at: 8 Data bits, Even Parity, 1 Stop bit (8E1)
  baud: 19200
  dataBits: 8 # since v1.2.0
  parity: "even" # no, even (default), odd - since v1.2.0
  stopBits: 1 # 1 (default), 1.5, 2 - since v1.2.0
  slaveId: 1
  port: /dev/ttyUSB0

# Mapping from LoRaWAN Sensors to Modbus Registers
  # LoRaWAN Sensor parameters
  - devEUI: 0000000000000000
    appKey: 00000000000000000000000000000000
    # Chirpstack Device Profile to use. Includes the Payload Parser.
    devProfile: lobaro-environment
    devName: "name of device in chirpstack"
    # Register mapping for this device
    # One device can fill any number of registers.
    # The server will check for overlapping definitions on start.
        # Modbus Address (do NOT prefix with 0, else it's octal)
      - addr: 1
        # The value to be mapped.
        # Usually the value is taken from the Chirpstack Parser result JSON
        # and can be selected via JSON Path as handled by https://github.com/tidwall/gjson
        # There are some special values:
        # @age - age of last update in minutes (for any register of this device)
        # @now - Current time as Unix Timestamp
        value: "@age" # age of last update in minutes (for any register of this device)
        # Data type of the value. Default byte order is LittleEndian
        # Supported types are: int16, uint16 (more will come in future versions)
        type: int16
        # The value is only for messages on the specified port, 0 for "every". Default: 0
        port: 0
        # The register value is multiplied with the given factor, 0 is irgnored. Default: 1
        factor: 1

      - addr: 2
        port: 1 # status packet
        value: "object.vBat"
        type: int16
        factor: 1000
      - addr: 3
        port: 2
        value: "object.temperature"
        type: int16
        factor: 10
      - addr: 4
        port: 2
        value: "object.humidity"
        type: int16
        factor: 10
      - addr: 5
        port: 2
        value: "object.pressure"
        type: int16
        factor: 10
      - addr: 6
        port: 2
        value: "rxInfo.0.rssi"
        type: int16
      - addr: 7
        port: 2
        value: "txInfo.dr"
        type: int16
	  - addr: 8
		port: 128
		value: "0x0102" # value to be sent as downlink, either as hex (prefixed with "0x") or base64 string
		type: downlink

  # A second device as example
  - devEUI: 0000000000000000
    appKey: 00000000000000000000000000000000
    devProfile: lobaro-one-wire
      - addr: 100
        value: "@age" # age of last update in minutes (for any register of this device)
        type: int16
      - addr: 101
        port: 1 # status packet
        value: "object.vBat"
        type: int16
        factor: 1000
      - addr: 102
        port: 2
        value: "object.sensors.0.temp"
        type: int16
        factor: 10
      - addr: 103
        port: 2
        value: "rxInfo.0.rssi"
        type: int16
      - addr: 104
        port: 2
        value: "txInfo.dr"
        type: int16
      - addr: 105
		port: 128
		value: "dGVzdF9kb3dubGluaw==" # value to be sent as downlink, either as hex (prefixed with "0x") or base64 string
		type: downlink
	  - addr: 106
        type: downlink-var
        len: 5 # 107-111

Send a predefined downlink packet to a configures port to a LoRaWAN device with a single write to a modbus register.

      - addr: 8
        port: 128
        value: "0x0102" # value to be sent as downlink, either as hex (prefixed with "0x") or base64 string
        type: downlink

Set the register to type "downlink" to allow sending the "value" via LoRaWAN to the deivce.

With the example above:

  • Write any value to modbus register with address 8
  • A downlink "0x0102" will be queued on port 128
  • The register will keep the written value in case of success. In case of error the value will be 0.

Send variable downlinks to a variable ports. Payload must be written to a set of defined modbus registers per LoRaWAN Device.

First, specify a new register under the device of your choice with type downlink-var. Then, set the following options for it:

  • Len: How many modbus registers (following this register) should be assigned as storage for the variable downlink.
  • Confirm: Whether to ask the device for acknowledgement of reception of the sent downlink (false or true)

	  - addr: 123
        type: downlink-var
        len: 7 # storing in registers 124-130
        confirm: true

The resulting structure at the configured address addr will be:

Downlink TriggerDownlink data...Downlink data

After (re-)starting the modbus server to apply the new config:

  1. Write your desired downlink (bytes) to the downlink data registers, starting at addr+1.
    1. You can only write 2 * len bytes at maximum! Extra bytes will be discarded.
  2. Optional: Write 0x0000 to the downlink trigger register at addr to clear the register (no downlink will be queued!)
  3. Write <port><length> to the downlink trigger register at addr, using 1 byte each for the designated FPort and downlink length in bytes.
    1. Example: Send downlink to port 128 (0x80), 10 (0x0A) bytes long: Write value 0x800A to register addr.

To check if the downlink was successful, read the trigger register and check its value:

  • Register value = <port><length>: The downlink was successfully queued. 
  • Register value = 0: The downlink couldn't be queued for your device. Check the server log for more details.


The gateway uses a local Chirpstack server. Access management interface on https://<gw-ip>:8080.

Documentation can be found on Chripstack.io.

For each type of device the lobaro-modbus-server needs to reference a Device Profile. See: Chirpstack Device Profile Management. The Device Profile of each LoRaWAN device must be referenced by its name or UUID in the lobaro-modbus-server.yml config file.

Gateway administration

When ever any file on the SD-Card need to change make sure to execute 


Change password

Login via SSH (see: Remote access)


Change IP address


sudo vim /etc/network/interfaces

pi@LoRaGateway:~ $ cat /etc/network/interfaces
# 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'

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

auto lo
iface lo inet loopback

# DHCP (Default, comment line to disable DHCP)
iface eth0 inet manual

# Fixed IP (Uncomment to enable or use /etc/dhcpcd.conf)
#auto eth0
#iface eth0 inet static
#    address
#    gateway


sudo vim /etc/dhcpcd.conf

Edit last lines to:

# RAK_eth0_IP
profile static_eth0
static ip_address=
static routers=

interface eth0
fallback static_eth0