Author Topic: Wireless RS485 communication  (Read 533 times)

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Offline Yaroooo

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Wireless RS485 communication
« on: September 16, 2020, 09:14:06 am »
I'm looking for a solution to connect two devices that communicate between them using RS485 . It's not a professional application and I'd like to adopt this solution because I can't place a wire between rooms. So most economic solution would be the best. I've also WIFI that can be used as a bridge on local network.

Actually I've found something like RS485 to WIFI, but it's like push only device. I'd like something like "RS485->Wireless->RS485" or "RS485-> WIFI WIFI->RS485".

Does someone have found and used such devices?
 

Offline H.O

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Re: Wireless RS485 communication
« Reply #1 on: September 16, 2020, 10:22:42 am »
I've been using two of the SX1278 based trancevicer modules, EBYTE E32-DTU-433L20 to be precise. I'm using them as a cable replacement from the basemement to the attic where I've got a couple of sensors speaking MODBUS RTU over RS485.

In short, whatever you put in at one end comes out the other (and the other way around) but they do "packetize" what you send so there can/will be some delay/latencies involved that you obviously won't have with a cable and I can't say how they'll cope if you throw it kB of data at once or how they'll work with a continous stream of data.

For my application, polling a MODBUS node once a minute it's been working extremely well for the last 18 or so months.
 

Online TheMG

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Re: Wireless RS485 communication
« Reply #2 on: September 16, 2020, 01:30:40 pm »
These work quite well in my experience but might be a tad out of your price range unless you can get a good price on a pair of used ones somewhere...

https://www.digi.com/products/networking/gateways/xtend-900mhz-rf-modems
 

Offline S. Petrukhin

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Re: Wireless RS485 communication
« Reply #3 on: September 19, 2020, 04:43:52 pm »
I'm looking for a solution to connect two devices that communicate between them using RS485 . It's not a professional application and I'd like to adopt this solution because I can't place a wire between rooms. So most economic solution would be the best. I've also WIFI that can be used as a bridge on local network.

Actually I've found something like RS485 to WIFI, but it's like push only device. I'd like something like "RS485->Wireless->RS485" or "RS485-> WIFI WIFI->RS485".

Does someone have found and used such devices?

RS-485 is just a physical environment. You can install any other SERIAL TTL Converter instead of the RS-485 chip, for example, LoRa is for point-to-point communication. Using WiFi can cause problems, because This network is not a real-time environment, transmission is carried out in packets, and protocols over RS-485 are often very critical to timings. To transmit packets over WiFi, you will need to take care of full buffering on both sides.
And sorry for my English.
 

Online Benta

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Re: Wireless RS485 communication
« Reply #4 on: September 19, 2020, 06:24:39 pm »
RS-485 is just a physically extended RS-232 communication with differential signaling.

The simplest solution in your case is buying a couple of Bluetooth modules with embedded SPP. SPP would allow this configuration:

Logic-level RS-232 <-> wireless <-> Logic-level RS-232.

BT modules with SPP cost 5...10 €.

« Last Edit: September 19, 2020, 06:28:23 pm by Benta »
 

Offline Kjelt

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Re: Wireless RS485 communication
« Reply #5 on: September 19, 2020, 09:50:11 pm »
RS-485 is just a physically extended RS-232 communication with differential signaling.
Exactly and the differential signaling means two wires with opposite signal value where at the receiver both signals are differentiated such that any noise on the signal will influence both wires and due to the differentiation the induced noise will be eliminated.
And therefore this can in theory never be realised wirelessly where a too large noise will eliminate the reception of the original signal  :)
Even to be more precise, when you divert from using two differential wires for transmission it is per definition no longer RS-485 , therefore the problem should be redefined.

What a beautifull trick question for an exam.
« Last Edit: September 19, 2020, 09:54:09 pm by Kjelt »
 


Offline AndersJ

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Re: Wireless RS485 communication
« Reply #7 on: September 21, 2020, 12:46:33 pm »
RS-485 is just a physically extended RS-232 communication with differential signaling.

Incorrect.
RS-485 is a half duplex interface.
"It should work"
R.N.Naidoo
 

Offline Kjelt

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Re: Wireless RS485 communication
« Reply #8 on: September 21, 2020, 01:21:27 pm »
RS-485 is just a physically extended RS-232 communication with differential signaling.

Incorrect.
RS-485 is a half duplex interface.

There are RS485 full duplex topologies but they need four wires two for Rx and two for Tx 1

1
https://en.wikipedia.org/wiki/RS-485#Full_duplex_operation
Quote
RS-485, like RS-422, can be made full-duplex by using four wires.[8] Since RS-485 is a multi-point specification, however, this is not necessary or desirable in many cases. RS-485 and RS-422 can interoperate with certain restrictions.[9]

 

Online bsdphk

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Re: Wireless RS485 communication
« Reply #9 on: September 21, 2020, 05:24:26 pm »
Full duplex RS-485 is called RS-422, and that actually came first.
 

Offline Kjelt

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Re: Wireless RS485 communication
« Reply #10 on: September 21, 2020, 09:06:53 pm »
Full duplex RS-485 is called RS-422, and that actually came first.
I don't think so, RS485 full duplex is still a multi point protocol, RS-422 is a single point to point protocol.
 

Online Benta

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Re: Wireless RS485 communication
« Reply #11 on: September 21, 2020, 10:04:18 pm »
Interesting to see how a simple question from the OP ("how do I replace a cable that at this point is RS-485 with a wireless connection") has degenerated to pointless bickering about RS-485 signalling.

I suspect that the OP has already run away.

 


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