Modbus <-> MQTT bridge for node-red

[nzfarmer]

As protocols go, Modbus is an older synchronous one that doesn't necessarily lend itself to the inherently asynchronous world of node-red and mqtt messaging.

However, a modbus-in, modbus-out, and modbus-config nodes are high on my list of nice to haves right now.

Anyone know of a project or code in existence? If not I'll roll my own.

thanks

[Edward Vielmetti]

There's some MODBUS code in node.js here:

https://github.com/TooTallNate/node-modbus-stack

I'm interested in whatever you come up with.

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[nzfarmer]

Cool I'll take a look. My initial thoughts were to sit on top of this one:

https://github.com/dresende/node-modbus-tcp#example

As for the UI, there is nice mapping of Function code type to input or output.

How we map multiplier register reads is a different question.

[Lawrence Griffiths]

That Git is quite old

You might want to look at these in NPM they both have updates in the last few months and regular downloads

https://www.npmjs.com/package/modbus

And if your doing just TCP

https://www.npmjs.com/package/modbus-tcp

>>How we map multiplier register reads is a different question

The the modbus-tcp libary returns an array

[nzfarmer]

Great to see some interest and alternatives for the protocol stack.

Would appreciate some use cases and any thoughts on error handling with an async context. 

Naive thoughts for the config node are:

1. a flag to denote input or output.

2.  function code -  limited to read or write mode i.e a drop down for modbus-in would provide:

• readCoils
• readDiscreteInputs
• readHoldingRegisters
• readInputRegisters

3. the start register

4. number of bytes/words (if applicable)

5. data format (string, int, etc.)

6. name of topic (overwritten by register address if null - payload of course becomes the register value for the input node)

Note: the above parameters will be constrained by the function code.

[Lawrence Griffiths]

All good have few questions

A.  1. a flag to denote input or output. not sure of the why you need to know?

B.  4. number of bytes/words With the modbus interfaces I've used you specify length & the interface does the rest 

[nzfarmer]

A.  1. a flag to denote input or output. not sure of the why you need to know?

Was just looking re use code for the Modbus in and Modbius out nodes. I noticed in node-red that you can add default properties when defining a config node so we can pass a flag and that controls the UI setup to be in modbus-in or modbus-out mode.

B.  4. number of bytes/words With the modbus interfaces I've used you specify length & the interface does the rest

 

Ok cool. I'll check a few more UIs.  My experience with Modbus has been mainly via APIs.  From memory there are a few free clients / simulators about 

[Dave C-J]

The config node should (IMHO) be about the common bits ie. the shared connection, underlying hardware ports, etc... anything in or out specific should be in the in or out nodes themselves ... but I may be missing something. (don't know Modbus :-)

[nzfarmer]

Good point.  Some form elements will be specific to each node.  But then there is question of the actual registers.  Should these be cofig nodes?  hmmm.

[nzfarmer]

This is where I've got to on the spec.  Am searching from some time to be able to start on this as we are close to the release of our new service.

Any one interested in crowd funding / sponsoring the work let me know.

Latest spec below - just a brain dump really so feel free to add comments.  It struck me that modbus-in can work in either slave or master mode, the only difference is whether it polls its own registers from a listening slave, or an external slave. 

Overview: 

- Create 3 nodes:  modbus-in; modbus-out; modbus-config.  

- Use modbus node: https://www.npmjs.com/package/modbus for protocol stack

- This uses the node libmodbus libraries:  https://github.com/tuxnsk/nodejs_libmodbus

- modbus config would have default settings to assist in its form creation and would expose the context and connection/config parameters.

.html for config nodes

- Modbus TCP needs to be unique by IP Address and Port, Max connections (default 1)

- Modbus RTU needs to be unique by slaveId, device and baud

- Specify whether slave or master (modbus-in only)

- Config node needs a name and label identifying type and paramaters.

- both config nodes expose their connection params, name and ctx (connection object), mode (slave / master) - see server.js example

.js for config nodes

Create a modbus slave server; Estabish and listen to connection; or warn.  Make ctx available to owner node.

For slave mode need to be able to bind to address

For master mode, needs to be able to handle disconnects and reconnect

.html form elements for modbus-in  node-red html interface

- Name (required)

- Topic - default function code + register i.e. 40001, or overwritten by mqtt topic definition

- Function Code (limited to read for read/write registers ) required

- Register value (uint 0-9999) required

- Length (uint number of 16bit registers - default 1) required

- Type ( integer , decimal(float), hex, bit ) use radio buttons. default integer?

- Poll interval (milliseconds)

- Inject message even if unchanged (checkbox)?

.js for modbus-in

require modbus

on start and poll

check value of register(s) defined in html - ctx.getReg

if new or changed (and report if unchanged)

format register value as type (use JSON [address,value] or [[addressx,value],[addressx+1,value]] where length >1)

send message

Outputs 1. Topic + Payload (register value + length cast as type)

.html form elements for modbus-out node

- Name (required)

- Function Code (uint limited to write only or read/write registers ) not mandatory

- Register value (uint 0-9999) not mandatory

Note: above paramaters can be overwritten by incoming topic if not set. i.e. 40001

- Type ( integer , decimal(float), hex, bit )

.js logic for modbus-out

listen for on('message',...)

perform any type casting operations and validations - i.e. isInt()

derrive function code and register from topic and/or node params

perform ctx.setBit,ctx.setReg operations etc. based on html form elements

flag any errors

Inputs 1:Topic (i.e. 40001) +  Payload (value)

Outputs 1. Logging of operation

[Lawrence Griffiths]

Andrew, a quick response

What is your hardware platform?

If it's a Raspberry PI then for RTU//ASCII you will need to a TTL serial to 4 wire RS422 and 2 wire RS485 converter.

In the past I've used an cheap Modbus TCP to RTU/ASCII device this one is 80 GBP 

https://www.expertdaq.co.uk/converter/modbus-tcp-modbus-rtuascii/ex-9132c-2-mtcp/

That way it becomes a lot simpler you just need to support Modbus TCP.

The converter can be set to RUT master or slave.

As to crowd funding I've considered that before for NodeRed.

What there doesn't seem to be is a Kickstarter for ad hoc projects.

Would be happy to make a small contribution to TCP support.

Also with Mobus TCP you get access to a lot of Protocol converters

RTA make some good converters these give supply NZ  

Example TCP Client to BACnet client

http://techstep.com.au/tech-step-gateways/460msbs/?gatewayfrom=Modbus%20TCP%20Client&gatewayto=BACnet/IP%20Client

Lawrence

[nzfarmer]

Thanks Lawrence

Let's exclude RTU from scope for now.

Have created Github project and will canvas out source for market for quote.

See:

https://github.com/nzfarmer1/node-red-modbus

[Mika Karaila]

I have already working implementation from the last year. I will make presentation how to connect MODBUS and OPC UA.
Presentation will be 18.3.2015, look: http://xxi.automaatioseura.fi/
I will provide examples in April...

[Lawrence Griffiths]

Mika good news on both front's.

I've seen one company implement some basic OPC UA features in a node function.

Assume you've created NR nodes for both Modbus and OPC UA ?

Lawrence

[Mika Karaila]

Yes and some other, it is just so easy to reuse them. ..
There are additional tricks that I found.

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[nzfarmer]

That's great Mika

Any chance of posting your code somewhere now so that we can decide what approach to take?

[Mika Karaila]

I´m actually on winter vacation this week, I will check this next week.

Perhaps I can upload modbus implementation + some instructions to github.

BUT I would like to refactor it. I would like to use more topic than special fields in the msg...

Br,

Mika

On Wed, Feb 25, 2015 at 9:47 PM, nzfarmer <southwebn...@gmail.com> wrote:

That's great Mika

Any chance of posting your code somewhere now so that we can decide what approach to take?

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[Mika Karaila]

Almost done, one problem pop out as I extended and refactored code.
I am using jsmodbus and I had to modify it...
I will check fi it is possible to leave something out and use original code.
Br,
Mika

[nzfarmer]

Hi Mika

Any update on this?

Thanks

[Mika Karaila]

I sent you zip last night, did not you receive that ?

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[nzfarmer]

Hi Mika

Thanks for that!

No not yet? I'll send another email address to you privately.

[Bluefox Fox]

Hello there,

What is the status? Stopped or will be developed?

Thank you,

Bluefox

вторник, 17 марта 2015 г., 8:41:23 UTC+1 пользователь nzfarmer написал:

[Mika Karaila]

Working, but only on evenings. I would like to solve function codes 15 & 16. I just do not have much time to work with this now. After a week or two I will look again...