Help with Modbus


I’m attempting to control a ventilation system which supports modbus communication. I have a cheap rs485 to USB adaptor and the following configuration:

    name: mvhr
    type: serial
    method: rtu
    port: /dev/serial/by-id/usb-FTDI_FT232R_USB_UART_AG0KB7RX-if00-port0
    baudrate: 9600
    stopbits: 1
    bytesize: 8
    parity: N


  - platform: modbus
      - name: mvhr_outside_temp
        hub: mvhr
        unit_of_measurement: °C
        slave: 1
        register: 11

and this is the modbus description from the user manual:

  1. Properties
    Control board uses Modbus RTU protocol via RS485 connection. The unit works as Slave and the information can be taken
    from an external Master module.
    Connection information of the unit is listed as below:
    Connection Type: Modbus RTU Slave
    Standard Address: 1
    Link speed: 9600
    Party: None
    Data Bits: 8
    Stop Bit: 1

I’m not having any luck getting readings from the sensor though. It just displays unknown.

After doing a bit of reading I’ve found out that not all rs485 usb adaptors are compatible, maybe this is the problem.

Also the wall controller for the ventilation system runs on modbus too so maybe there is an address conflict. I cant find any info on the standard address for the wall controller.

Unfortunately I’m trying to do this remotely as the system isn’t at my house which makes it hard to do too much physical testing but any ideas would be much appreciated!

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