maticdiba
Posts: 2
Joined: Wed Oct 10, 2018 7:16 am

Two wire cable for networking

Wed Oct 10, 2018 7:21 am

Hi,
I am new to Raspberry and now that I got the first touch of it, I would like to know if there is a way to use it for a more complex problem.

I have location A and location B connected with two wire cable. The distance between the two locations is aproximately 2km. Is there a way to use this cable and two Raspberry units to use them for communication? Did anyone try to do something similar. Right now this cables are used for communication via "Field phone". It would also be hard to replace this wire with any other wire.

I think this could be a great project to start using Raspberry for real, if it's even possible :)

For any suggestion about how to find the solution, I would be more then thankful.

wolf.z
Posts: 85
Joined: Thu Dec 24, 2015 8:34 pm

Re: Two wire cable for networking

Wed Oct 10, 2018 9:13 am

DSL modems come into my mind. However, I never did try that:

Search for the phrase "DSL master-slave pair" or SDSL/SHDSL modem like
https://www.digicomm.de/en/products/shd ... rnetmodem/ or
https://www.allnet.de/en/allnet-brand/p ... sterslave/

That may work.

fruitoftheloom
Posts: 17603
Joined: Tue Mar 25, 2014 12:40 pm

Re: Two wire cable for networking

Wed Oct 10, 2018 9:34 am

maticdiba wrote:
Wed Oct 10, 2018 7:21 am
Hi,
I am new to Raspberry and now that I got the first touch of it, I would like to know if there is a way to use it for a more complex problem.

I have location A and location B connected with two wire cable. The distance between the two locations is aproximately 2km. Is there a way to use this cable and two Raspberry units to use them for communication? Did anyone try to do something similar. Right now this cables are used for communication via "Field phone". It would also be hard to replace this wire with any other wire.

I think this could be a great project to start using Raspberry for real, if it's even possible :)

For any suggestion about how to find the solution, I would be more then thankful.


You may be able to connect via UART Serial:

https://scribles.net/setting-up-uart-se ... berry-pis/
Adieu

scotty101
Posts: 3184
Joined: Fri Jun 08, 2012 6:03 pm

Re: Two wire cable for networking

Wed Oct 10, 2018 10:24 am

fruitoftheloom wrote:
Wed Oct 10, 2018 9:34 am
You may be able to connect via UART Serial:

https://scribles.net/setting-up-uart-se ... berry-pis/
This would mean utilising something like RS485 but the maximum distance for that is 1220m so a repeater would be required.
Electronic and Computer Engineer
Pi Interests: Home Automation, IOT, Python and Tkinter

wolf.z
Posts: 85
Joined: Thu Dec 24, 2015 8:34 pm

Re: Two wire cable for networking

Wed Oct 10, 2018 3:23 pm

That is two different approaches.

DSL modems will give a full fledged IP Network bridge. With that modems you'll get everything in one box: Hardware and software and basically a no-brainer setup.

When it comes to EIA 232/422/485 communication, yes, that's kind of networking. But you won't get a no-brainer near IP network setup. What you'll need:
Low voltage TTL (Raspberry) UART to EIA 485 physical convertors.
Something implementing the basic EIA 485 bus protocol. You may either involve two physical converter+protocol translator piece of hardware or implement the EIA bus protocol in software. The link leads to a connection via UART, but that's a full duplex wiring. It is EIA 232-single-wire each direction plus ground =3wires. EIA 485 uses 2 wires for one direction. With two wire cable only you'll have to use those 2 wires for each directions or set up a simplex connection. You'll have to install something like modbus. The solution given by the link will not work for a 2 wire cable with EIA 485 convertors.

If you read about maximum cable length: This is totally dependet on the bitrate you want. Either DSL or EIA485 should work over 2km, with DSL targetting about a few Mbit/s, EIA 485 targetting som 10 Kbit/s. Well, it should.

maticdiba
Posts: 2
Joined: Wed Oct 10, 2018 7:16 am

Re: Two wire cable for networking

Wed Oct 17, 2018 7:22 am

Thanks for all the answers.

As wolf.z mentioned, fruitofthelooms solution wouldn't work because there are only two wires. Distance is not a problem, because I could put a repeater inbetween.

Also the solution with DSL modem looks like it would work, but I was trying to find out, if it's possible to achieve full duplex just with raspberry pi and additional modules. I guess there is no existing module that would modulate signal on single pair wire for raspberry, like DSL modem does?

wolf.z
Posts: 85
Joined: Thu Dec 24, 2015 8:34 pm

Re: Two wire cable for networking

Wed Oct 17, 2018 10:01 pm

Well,

look, what the Raspberry brings with it. It is all typical computer interfaces, meant for rather local communications: SPI, I2C, EIA232, DPI, USB, HDMI, even Ethernet. That's all stoneage binary physics communication. GBit ethernet is the very first attempt to make things different but in scope of long range communication. When it comes to mid-range communications, you leave the physical binary domain, great people created by precisely defining the physical circumstances, needed for assumed digital operation. Beyond, you enter the world of communictaion technology.

If you want avoid additional hardware you likely fail, bridging 800m via copper phone twisted pair. Using those meant for 3kHz communication lines for Mbit speed, that's what DSL was developped for. It uses OFDM rather than stoneage binary coding. OFDM is the most effective method for using signal spectrum known. That's why DSL, WIFI, DVB-T, DAB, powerline, 4G LTE, virtually every latest communictaion technology uses OFDM.

Possibly involving directional wifi link was an alternative in your case (again, using OFDM), since 5GHz wifi plus directional antenna x two might be less expensive than two DSL modems. Anyway, you'd need direct line of sight. Take a look at wifi bridges just as Ubiquity nano station or Ligowave LigoDLB Propeller.

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