RS485 and relay output not working

  • Hello,

    I purchased an Axon M205 a few weeks ago. The hardware/software stack looks promising, but I cannot make it work.

    1. Serial issue

    When I plugs in a xS40 extension on RS485 1.3, it is not detected (no led blinking). When I use RS485 1.1, leds start blinking. Furthermore, in evok control panel, there is only one serial, while I am expected three of them (1 RS232 and 2 RS485). On system, there is only /dev/extcomm/0/0.

    When using RS485 1.1, no additional DI or RO appear in the control panel. Here is my configuration:

    global_id = 2
    device_name = xS40
    modbus_uart_port = /dev/extcomm/0/0
    neuron_uart_circuit = 1_01
    allow_register_access = True
    address = 15

    All DIP switches but the RS485-end are turned off.

    1. Relay output

    When using evok (or direct switch using appropriate DIY.X, or SysFS), I am able to get the RO led on. But it looks like that the contact is never made (I am not able to switch on any light - protected by a 2A circuit breaker). I don't know if the relay is supposed to do any "noise" on contact, but there is nothing.

    Note : my system is up to date (apt update/upgrade), but I am not using the latest OS image (

    I will appreciate any help!
    Thanks in advance!

  • Hi @bubuche,

    I'll reply to both your questions. Apologies for taking a while, I have not been available over the Christmas period.

    1. The upper board RS485/RS232 ports are accessible under /dev/ttyS(0-3) as opposed to /dev/extcomm/0/0. This is unfortunately a hardware limitation which we cannot work around easily.

    2. If the LED light turns on then the relay should have continuity across it; the LEDs are controlled by the same circuitry as the output itself. If there is no change in continuity across the output it may be due to some sort of a hardware fault. I should note that digital (as opposed to relay) outputs are transistor-based, and will not make any noise. The relays should issue an audible click however. Could you please post a quick schema of your installation as well? LED lights in particular can have a very high inrush current, which a slow-blow fuse may not neccesarily catch.

    I hope this helps

  • Hello,

    Thank you for your response!

    When switching to /dev/ttyS1 in evok.conf, everything works as expected on the xS40:

    • I have access to additional DI and RO in the control panel
    • Switching a RO produces an audible click

    Most importantly, I am able to turn on a light with the xS40 (using schema of page 17 of Neuron technical documentation). Looks good!

    Unfortunately, when I plug in the same connector on a RO of my Axon M205:

    • No audible click
    • There is no contact on the circuit (my light does not turn on)
    • Though, the led of the corresponding RO turns on

    All the RO I've tried behave the same. And note that I've never heard the xS40 contact noise on the Axon, even before playing with real circuits/current.

    From the System tab of the control panel:

    Neuron M205 S/N: 9

    Let me know if you need more details.

  • Hi @bubuche!

    Could you please try to switch the relay by writing '1' to the file /sys/devices/platform/unipi_plc/io_group2/ro_2_01/ro_value? You can do this via the commands:

    sudo su
    systemctl stop evok
    systemctl stop mervisconfigtool
    systemctl stop mervisrt
    echo "1" > /sys/devices/platform/unipi_plc/io_group2/ro_2_01/ro_value

    If this does not work then unfortunately it most likely is due to a hardware fault.

    I had a look at the testing logs for your unit, and it has passed tests without any problems, so, if the above does not turn the relay on, you may have to email support to arrange further steps.

  • Hello,

    No noise. No light. No luck.
    Only the green led turned on.

    So I suppose I have to contact support.

    Thanks for your help and quick answers !

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