Wireless RS485 communication - Page 1
Forum section: electronics / projects

author: Yaroooo
author_rank: Regular Contributor
timestamp: September 16, 2020, 09:14:06 am
content: 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?

author: H.O
author_rank: Frequent Contributor
timestamp: September 16, 2020, 10:22:42 am
content: I've been using two of the SX1278 based trancevicer modules,EBYTE E32-DTU-433L20to 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.

author: TheMG
author_rank: Frequent Contributor
timestamp: September 16, 2020, 01:30:40 pm
content: 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

author: S. Petrukhin
author_rank: Super Contributor
timestamp: September 19, 2020, 04:43:52 pm
content: Quote from: Yaroooo on September 16, 2020, 09:14:06 amRS-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.

author: Benta
author_rank: Super Contributor
timestamp: September 19, 2020, 06:24:39 pm
content: 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 €.

author: Kjelt
author_rank: Super Contributor
timestamp: September 19, 2020, 09:50:11 pm
content: Quote from: Benta on September 19, 2020, 06:24:39 pmExactly 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 signalEven 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.

author: ebclr
author_rank: Super Contributor
timestamp: September 21, 2020, 10:56:44 am
content: https://www.aliexpress.com/item/4001192825465.html?spm=a2g0o.productlist.0.0.23161468zt7wBe&algo_pvid=8a74efc0-f4ae-4603-9842-74dd5ae1c216&algo_expid=8a74efc0-f4ae-4603-9842-74dd5ae1c216-5&btsid=0bb0623016006857740062569e1a89&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

author: AndersJ
author_rank: Frequent Contributor
timestamp: September 21, 2020, 12:46:33 pm
content: Quote from: Benta on September 19, 2020, 06:24:39 pmIncorrect.RS-485 is a half duplex interface.

author: Kjelt
author_rank: Super Contributor
timestamp: September 21, 2020, 01:21:27 pm
content: Quote from: AndersJ on September 21, 2020, 12:46:33 pmThere are RS485 full duplex topologies but they need four wires two for Rx and two for Tx11https://en.wikipedia.org/wiki/RS-485#Full_duplex_operationQuote

author: bsdphk
author_rank: Regular Contributor
timestamp: September 21, 2020, 05:24:26 pm
content: Full duplex RS-485 is called RS-422, and that actually came first.

author: Kjelt
author_rank: Super Contributor
timestamp: September 21, 2020, 09:06:53 pm
content: Quote from: bsdphk on September 21, 2020, 05:24:26 pmI don't think so, RS485 full duplex is still a multi point protocol, RS-422 is a single point to point protocol.

author: Benta
author_rank: Super Contributor
timestamp: September 21, 2020, 10:04:18 pm
content: 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.