[SOLVED] How to config Modbus 8 relay board

Hello every one! Begginner here

This is my first question here. I have configured a SDM-630 watt metter and an EP-SOLAR charge controller over paper UI

Now im trying to configure a Modbus Relay board.After 2 days trying to configure it over Paper UI, i stucked at a point of the transformations.

I can read the relays state, i can turn it on by the switch on Paper UI but, it dont turn of in the switch

I have read many tutorials and infos here about modbus binding, but really dont understand. Maybe my english is not enough for that task. I speak portuguese.

My question is: HOW TO CONFIGURE that board to turn on-off with Paper UI ?



Umm, we don’t know. What board, cannot see it from here?

It would be a really good idea to share what you have done so far, especially as it works in part.
It would be an even better idea to share any documentation you have about the relay board, i.e. what is it expecting you to send to turn on relays?

thank you very much for the reply!

that is exactly like your answer on that post:


the relay is the same but it is 8 relays instead of 4.

but works in the SAME way.

i stucked in the part of the transformation of ON OFF and off to on.

How i do that on PAPER UI ?

My goal is to deviate solar panels from my ON GRID inverters to my charging string.

in brazil, they are not paying good for the net metered energy, soo i started a lithium power wall, conected to an EPEVER TRACER AN controller. i want to use NODE-RED LATER to process the inputs from the SDM630 WATTMETER, and them deviate panels from ongrid to charging string using this relay board.

I already started constructing the node-red flow i can compare the wattage passing thru SDM 630 on each phase and then make something. this make something is turning on and off some panels of the ON GRID string.

Okay. So what you want is to have an openHAB Switch type Item, and when that is commanded ON or OFF you want to send 256 or 512 to a modbus holding register?

Create a transformation file myweirdswitch.map


Define a modbus data Thing to include


among your usual writeType and address settings.

1 Like

worked PERFECTLY!!!

Created .MAP file inside transform folder.

no i have a switch that turn on and of relay 1

Man you are great developing openhab.

I do a donation for the project soon i can.


the only thing i see is the lack of documents explaining how to do it over PAPER UI. Maybe i will try to cooperate on that. everything here is using paper UI.


Not me, I’m just a user, but yes they have done a great job.

Hi guys!
I’m new to the forum and a bit of a novice. I am trying to configure a 32-relay shield but without success. I do it all for Paper UI.
The problem I have is that I cannot create the poller without a communication error. The error is:

Error with read: org.openhab.core.io.transport.modbus.internal.ModbusSlaveIOExceptionImpl: Modbus IO Error with cause = ModbusIOException, EOF = false, message = ‘I / O failed to write’, cause2 = null

I have tried to change the type (coil, discrete, holding and input) but without result.

Attached configuration:

I would be very grateful for a help.

Make a new thread, you clearly don’t have the same device as the original poster.

You’ll need to find out what your mystery relay shield wants. There are literally hundreds of thousands different ways to try at random.

All the information I have is this:

I have done tests with another controller (similar to OH) and I have gotten it to work with the FC6 function. All I have to do is send the value 511 or 512.

Could you help me to activate the relays with OH?

Thank you very much again

Then that’s what you need to reproduce in openHAB.
Are you using the same details in your Modbus serial bridge?

Device wanting FC3/FC6 functions tells us that you’d want to use holding type in your poller Thing.
The note says we can read from start address 1 length 16

The note says the on/off state will be returned as 0001/0000 which is ordinary enough.
So you can set up 16 data Things, and link their switch channels to Switch type Items without any bother.

Then we can look at writing.
For each data Thing we add some write details - holding type, same address.

We want to use FC06 and that should happen by default.
But you need to send special data, not 0001/0000.
That’s described in post above

you’ll need to have MAP transformation installed.

If you have trouble, show us your Things using <code> tab, screenshots are not as helpful.