RUTX11 Modbus MQTT

NETWORKING SOLUTIONS
9

I managed to do it.

After searching this community for relevant posts i managed to insert a client on my RUTX11:

opkg -e /etc/opkg/openwrt/distfeeds.conf update
opkg -e /etc/opkg/openwrt/distfeeds.conf install mosquitto-client-ssl

this will make it possible to install the pub sub client.

After that, using WinSCP i transfered to my RUT a library called ModPoll that allows me to make modbus requests to the PLC running a server, and get returns of data.

After that i implemented this code (shell script):

# MQTT Broker IP address
BROKER="broker_ip_address"
# MQTT Broker port
PORT="1883"
# MQTT topic to subscribe to
TOPIC="testmosquitto"
PUB_TOPIC="testmosquitto/data"

# PLC IP address (Modbus TCP slave)
PLC_IP="plc_ip_address"
# Modbus slave ID on the PLC
SLAVE_ID=1 (or 16#FF = 255)

echo "Starting MQTT listener..."

# Subscribe to the MQTT topic, pipe each received message to the while loop
mosquitto_sub -h "$BROKER" -p "$PORT" -t "$TOPIC" | while read -r payload
do
    # echo "$(date) Received: $payload" >> /tmp/mqtt_log.txt  # Uncomment to enable logging

    if echo "$payload" | grep -q "on"; then
        echo "Command: READ 5 holding registers starting at 40001 (addr 0), poll once"
        # modpoll -m tcp -a $SLAVE_ID -r 1 -c 5 -t 4 -1 $PLC_IP
        # Run modpoll once, capture output
        result=$(modpoll -m tcp -a $SLAVE_ID -r 1 -c 5 -t 4 -1 $PLC_IP 2>&1)
        # pub the full data 
        echo "Publishing Modbus data to topic $PUB_TOPIC"
       mosquitto_pub -h "$BROKER" -p "$PORT" -t "$PUB_TOPIC" -m "$result"
    elif echo "$payload" | grep -q "off"; then
        echo "Command: WRITE value 1 to register 40001 (addr 0)"
        modpoll -m tcp -a $SLAVE_ID -r 1 -t 4 $PLC_IP 255
    else
        echo "Unknown payload: $payload"
    fi
done

And this is the outcome:

  • Basically i publish the word “on” and that will generate a modbus request to the server running on my PLC, and return the data to the script that will publish to my broker the information (i didn’t format the message yet…)
    Captura de ecrã 2025-07-01 110102
    Captura de ecrã 2025-07-01 110102894×308 33.9 KB

But feel free to implement in any way you need.
I recommend checking the tutorial on shell scripting by Teltonika itself.
(And use chatGPT :shushing_face:)

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