Virtual Modbus RTU /dev/USB0 not visible

[chris74]

Hello everyone,

I am using a RevPi Core S8 with Buster V10.

I would like to use an Arduino to read existing sensors via i2c. Both boards are connected via USB and the Arduino is integrated via a virtual Modbus RTU master.
This procedure was outlined in https://revolutionpi.de/blog/maker-herz (german article).

The settings in Pictory were made accordingly, I would like to read out 20 words, and the com settings are among others device_path=/dev/ttyUSB0.

Unfortunately, /dev/ttyUSB0 is not visible in the operating system, but that would be necessary to "pick up" the data in the process image, right?

I would be grateful for any support / suggestions.

Thanks,
Chris

[dirk]

Hi Chris, can you make a sketch of your setup? I recommend you try the communication as in the video tutorial #22 with the QModMaster software instead of PiCtory Modbus Client (formerly Master) first to check your wiring:
https://revolutionpi.com/tutorials/video-tutorials#VT22

[chris74]

Hello Dirk,

To establish a connection with an Arduino, I did the following.

For the wiring, the Revpi and Arduino are connected directly with an USB cable.
For a Modbus RTU Slave device on the Arduino side, I download the sample sketch "Arduino Coupling" from the download page (https://revolutionpi.com/tutorials/downloads).
In the Pictory, I added a virtual Modbus RTU Master.

The device appears as:

Address: 0 module type: 95 (0x5f) RevPi Core V1.2
Module is present
input offset: 113 length: 6
output offset: 119 length: 5

Address: 31 module type: 96 (0x60) RevPi DIO V1.5
Module is present
input offset: 0 length: 70
output offset: 70 length: 18

Address: 64 module type: 24580 (0x6004) ModbusRTU Master Adapter V0.0
Module is present
input offset: 124 length: 101
output offset: 225 length: 73

The Arduino appears as /dev/ttyACM0.

Maybe I'm wrong, or maybe there are other, cleverer ways to interconnect both devices.

However, the video you sent me follows another approach, as the Revpi is configured as a Modbus TCP Slave, right? If this is the better way to configure the Arduino as a Modbus TCP master, then I will take it.

Sorry for the very basic questions, but I've never done this before.

Thanks,
Chris

[dirk]

Hi Chris, ok maybe I made a mistake here because it would be clear to me that the communication via Modbus-RTU should work via RS485 and not via USB, but perhaps I was wrong on that assumption. I need to get this working with a compatible Arduino board and will get back to you. I have an incompatible Arduino Due here - it doesn't compile. Thanks for your patience.

[chris74]

Thanks Dirk,

meanwhile, I have come one step further:
I am still using the Modbus RTU Slave device on the Arduino side "Arduino Coupling" from https://revolutionpi.com/tutorials/downloads.
Based on (with modifications)
https://blog.mbedded.ninja/programming/ ... ing-c-cpp/
I am using C/C++ Linux' serial port functions to read out the data stream on the Revpi side. But it needs still some tweaking.

It is still a workaround and needs to be optimized for integration into the process image. So I will continue to work on it .....

Thanks,
Chris

[dirk]

Hi Chris, thank you for your positive feedback.