ESPHome modbus integration to Recom 2S Ventilation unit

[paulius2k]

Hello,
first - THANK you for developing this integration. You guys are great!

I am fresh in the Modbus protocol - maybe someone could help me here, or kindly redirect to some place to do my RTFM.

The control panel (the screen) of my Recom 2S Ventilation unit (https://www.rec-indovent.se/en/products/recom-2-a21/) is connected via RS485 to the main processing unit and the instruction says:

All devices must be connected to an RS-485 network in a multidrop bus. A single RS-485 network supports up to 16 units
simultaneously - and up to 16 control panel connections (for example, integration of one unit and multiple control
panels over an RS-485 network makes it possible to manage the unit from distributed control panels installed in
different rooms) .

I connected my "RS485 to TTL adapter" to the same terminal as the control panel - three wires A+, B- and GND.

The problem is - I cannot find any Modbus specification from this vendor.

So I am thinking - maybe I can listen-in and find something by trial-and-error, or... is that totally unrealistic?

I am using HA OS installation with core-2021.12.10; ESPHome v2022.1.0.

So my ESPHome configuration is:

esp32:
  board: esp32dev
  framework:
    type: arduino

logger:
  level: VERY_VERBOSE

uart:
  id: uart_modbus
  tx_pin: 17
  rx_pin: 16
  baud_rate: 115200 
  stop_bits: 2

modbus:
  id: modbus1
  uart_id: uart_modbus
  # flow_control_pin: 5

  
modbus_controller:
  - id: recom_2s
    ## the Modbus device addr
    address: 0x1
    modbus_id: modbus1
    # setup_priority: -10
    

sensor:
  - platform: modbus_controller
    modbus_controller_id: recom_2s
    id: _0x5002
    name: "0x5002"
    address: 0x5002
    register_type: holding
    value_type: U_DWORD
    state_class: "total_increasing"
    device_class: "energy"
    unit_of_measurement: "kWh"
    accuracy_decimals: 2
    filters:
      - multiply: 0.01

  - platform: modbus_controller
    modbus_controller_id: recom_2s
    id: _0x3001
    name: "0x3001"
    address: 0x3001
    unit_of_measurement: "V"
    register_type: read
    value_type: U_WORD
    accuracy_decimals: 2
    filters:
      - multiply: 0.01

I took these and a few other sensor descriptions from the example configurations, just to try.

What I get is:

• the requests are sent out, there is something coming back, but it still says "no response received":

[V][modbus_controller:036]: Sending next modbus command to device 1 register 0x3001 count 3
[VV][uart.arduino_esp32:148]:     Flushing...
[VV][uart.arduino_esp32:148]:     Flushing...
[V][modbus:184]: Modbus write: 01.04.30.01.00.03.EE.CB (8)
[V][modbus:184]: Modbus write: 01.04.30.01.00.03.EE.CB (8)
[V][modbus_controller:461]: Command sent 4 0x3001 3
[V][modbus_controller:461]: Command sent 4 0x3001 3
[V][modbus:058]: Modbus received Byte  255 (0Xff)
[V][modbus:058]: Modbus received Byte  197 (0Xc5)
[V][modbus:058]: Modbus received Byte  238 (0Xee)
[V][modbus_controller:036]: Sending next modbus command to device 1 register 0x3001 count 3
[VV][uart.arduino_esp32:148]:     Flushing...[0m
[VV][uart.arduino_esp32:148]:     Flushing...
[V][modbus:184]: Modbus write: 01.04.30.01.00.03.EE.CB (8)
[V][modbus_controller:461]: Command sent 4 0x3001 3
[D][modbus_controller:032]: Modbus command to device=1 register=0x3001 countdown=0 no response received - removed from send queue

in addition to that I am getting a constant flow of some Modbus reads, e.g.:

[...]
[V][modbus:058]: Modbus received Byte  195 (0Xc3)
[V][modbus:058]: Modbus received Byte  208 (0Xd0)
[V][modbus:058]: Modbus received Byte  204 (0Xcc)
[V][modbus:058]: Modbus received Byte  245 (0Xf5)
[V][modbus:058]: Modbus received Byte  245 (0Xf5)
[V][modbus:058]: Modbus received Byte  91 (0X5b)
[V][modbus:058]: Modbus received Byte  95 (0X5f)
[V][modbus:058]: Modbus received Byte  49 (0X31)
[V][modbus:058]: Modbus received Byte  120 (0X78)
[V][modbus:058]: Modbus received Byte  80 (0X50)
[V][modbus:058]: Modbus received Byte  246 (0Xf6)
[V][modbus:058]: Modbus received Byte  197 (0Xc5)
[V][modbus:058]: Modbus received Byte  238 (0Xee)
[V][modbus:058]: Modbus received Byte  95 (0X5f)
[V][modbus:058]: Modbus received Byte  95 (0X5f)
[V][modbus:058]: Modbus received Byte  195 (0Xc3)
[V][modbus:058]: Modbus received Byte  210 (0Xd2)
[V][modbus:058]: Modbus received Byte  84 (0X54)
[V][modbus:058]: Modbus received Byte  91 (0X5b)
[V][modbus:058]: Modbus received Byte  95 (0X5f)
[V][modbus:058]: Modbus received Byte  49 (0X31)
[V][modbus:058]: Modbus received Byte  120 (0X78)
[V][modbus:058]: Modbus received Byte  80 (0X50)
[V][modbus:058]: Modbus received Byte  246 (0Xf6)
[V][modbus:058]: Modbus received Byte  95 (0X5f)
[...]

This flow is quite intensive, as the connection to my ESPHome API is often dropping and restarting.
And it is happening only when I have the control panel (screen) of the unit connected to the bus.

When the control panel is disconnected, I only get some bytes to the request sent from the ESP:

[17:48:48][VV][uart.arduino_esp32:148]:     Flushing...
[17:48:48][V][modbus:184]: Modbus write: 01.03.50.02.00.02.74.CB (8)
[17:48:48][V][modbus_controller:461]: Command sent 3 0x5002 2
[17:48:48][V][modbus:058]: Modbus received Byte  1 (0X1)
[17:48:48][V][modbus:058]: Modbus received Byte  3 (0X3)
[17:48:48][V][modbus:058]: Modbus received Byte  80 (0X50)
[17:48:48][V][modbus:058]: Modbus received Byte  2 (0X2)
[17:48:48][V][modbus:058]: Modbus received Byte  0 (0X0)
[17:48:48][V][modbus:058]: Modbus received Byte  2 (0X2)
[17:48:48][V][modbus:058]: Modbus received Byte  116 (0X74)
[17:48:48][V][modbus:058]: Modbus received Byte  203 (0Xcb)
[17:48:48][V][modbus_controller:036]: Sending next modbus command to device 1 register 0x5002 count 2
[17:48:48][VV][uart.arduino_esp32:148]:     Flushing...
[17:48:48][V][modbus:184]: Modbus write: 01.03.50.02.00.02.74.CB (8)
[17:48:48][V][modbus_controller:461]: Command sent 3 0x5002 2
[17:48:48][V][modbus:058]: Modbus received Byte  1 (0X1)
[17:48:48][V][modbus:058]: Modbus received Byte  3 (0X3)
[17:48:48][V][modbus:058]: Modbus received Byte  80 (0X50)
[17:48:48][V][modbus:058]: Modbus received Byte  2 (0X2)
[17:48:48][D][modbus_controller:032]: Modbus command to device=1 register=0x5002 countdown=0 no response received - removed from send queue

So I am looking for some insights regarding:

• is it possible to decode the Modbus protocol of this specific vendor without having the specs, just by trial-and-error?
• can anything be parsed from this constant flow of received bytes?
• how should I further debug and fix my integration?

Thanks in advance!

[paulius2k]

@martgras - would you have any insights on this issue? thanks!