For reasons of availability, I have connected a passive (without external power supply) USB hub with 4 output ports to my MultiPlusII GX. As the GX in the Multi only supplies 500mA and I have also connected the galvanic USB isolation to the hub for each USB port, there is no reserve for a larger passive USB hub (if available). However, as the E340 energy meter is also connected there via RS485 Modbus, the idea was to also use this interface for the “Waveshare Industrial Modbus RTU 8-Ch Relay Module” with 8 relays and 8 inputs. In the Modbus specification it can be read that this protocol has a transmission protection with CRC16. Since the connected modules only respond if everything is correct, the use of different bit rates on the same physical line should not be a problem.
As I also have a CerboGX development system in addition to my live MultiPlusII GX system for testing such things, I first tried to get the Modbus interface to work on the CerboGX. However, I don’t have an E340 or any other peripherals such as inverters, SmartShunts etc. connected there. So it should be the simpler option.
To use the Modbus interface, I connected an RS485 adapter to the Cerbo on USB0, exactly as described here RemoteGPIO (ex venus_rgpio) now released in v3.2.1 - VictronEnergy
is described.
In parallel, I also have an RS485 adapter on the Modbus interface, which is connected to a terminal on a PC with “HexTerm” so that I can monitor the data traffic.
Commissioning the communication between the terminal and the relay module worked without any problems. The communication between the PC terminal programme and the relay module works exactly as described here https://www.waveshare.com/wiki/Modbus_RTU_Relay_(D).
So the next step was to get the RemotGPIO functionality working with the CerboGx.
After preparing and installing the packages, which is described here RemoteGPIO (ex venus_rgpio) now released in v3.2.1 - VictronEnergy, I can at least switch the relay ports “internally” with Node Red.
However, after configuration (ID = 1) and activation of the RemoteGpio service, I could not observe any communication on the RS485 interface. The only thing that could be observed cyclically was a sequence of
approximately every second.
What is not quite clear to me: Why is an IP address required for Modbus RTU? There is also no way to switch the communication to Modbus RTU. So I configured the address from the example. Unfortunately without success. I also tried the configuration of
from this amount RemoteGPIO (ex venus_rgpio) now released in v3.2.1 - VictronEnergy
Even with Node Red via the built-in Modbus blocks, I could not find a configuration that leads to cyclic data communication on the USB0 interface. For a short time I was able to write directly via System Command Promt:
sudo echo “ABCDE” >> /dev/ttyUSB0
I could see the characters “ABCDE” on the interface with 9600Bit/s. But then there is another process that reconfigures the interface to 4800Bit/s.
Attempting to stop this process with the command:
/opt/victronenergy/serial-starter/stop-tty.sh ttyUSB0
failed because the USB0 directory does not exist.
So I’ve reached the end of my experiments and could use some hints and help for setting up the CerboGX.