Problems to configure Dragino RS 485 LN Modbus to Lorawan

[Maria Dostert]

Hello everyone,

I am using the Dragino RS485-LN (Modbus to LoRaWAN) for the first time. The connection to TTN is working perfectly fine (Join is successful, regular uplinks), but I am not receiving any data from my meter.

The meter is a "CS Instruments VA520" flow meter.
Here is what I have configured so far:
- Baudrate: 19200
- Parity: EVEN (AT+PARITY=2)
- Stop bits: 1
- Modbus Slave ID: 1 (verified)

To query the flow data, I sent the following downlink command on FPort 1:
AF 01 01 06 01 03 03 E8 00 02 01
(According to the manual, the flow rate is on Holding Register 1001, so I used 1000 / 03E8).

No matter what I try, the TTN live data always shows:
"frm_payload": "Af//////////"  (Modbus Timeout)
or sometimes just "AQ==" (which decodes to 01, so an empty payload header).

Hardware troubleshooting done so far:
- I already tried swapping the RS485 A and B wires, but the timeout remains.
- Currently, GND_485 is left unconnected (only A and B are connected).

Do you have any ideas what I might be doing wrong? Am I missing something in the Dragino configuration or could it be an electrical/GND issue?

Thanks in advance for your help!