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Transmitting low bandwith data through long, non-ideal cables

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Renaud:
HI everyone,

I have a small challenge: I have a long multicore cable (assuming shielded) that goes through a building (say 100m).
That mutlicore only carries some 110VDC voltages and low currents (for buttons, switches, indicator lights).

Now I would need to send some data from a sensor through some of the unused spare cores of this cable.
The bandwidth can be very low but I need to reliably get the data without risking introducing big issues in terms of EMI.

Since the cores are not twisted, RS485 may not be suitable so I was wondering if there was any existing transceivers for this type of low bandwidth data transmission across non-ideal cables.
I was thinking about some very low frequency frequency modulation carrier could work but I'm not even sure anything like this is even workable.
The sensor would be queried every few seconds and just needs to return a measurement.

Surely I'm not the first facing this problem, I'd rather not have to pull cables :)

Thanks for any pointers!

pqass:
20mA current loop is ideal for sensors over long distances in harsh environments.
Only requires 1 pair and if the sensor is low power, can even power it.

https://www.google.ca/search?q=20ma+current+loop

There is a whole industry around the sensors and controllers.  Although it's primarily an analog system, a low bandwidth digital protocol has been developed on top it; Hart protocol. 

My only direct experience has been with designing a home automation sensor network for myself so I can't direct you to commercial solutions.  I don't know if you are, like myself, designing both endpoints or wishing just to purchase off-the-shelf.

KrudyZ:
100 m isn't really all that long. RS485 can easily span that even at fairly high data rates.
You can get slew rate controlled drivers if you are concerned about interference.

mariush:
I imagine ethernet over copper pair (vdsl) converters would work just fine, but they'd be expensive...
example :
https://www.amazon.com/dp/B01BOD8C9W/
https://www.amazon.com/PLANET-VC-231-Ethernet-VDSL2-Converter/dp/B009WWHNWU

100 meters is the maximum length of ethernet ... you have 8 conductors. At 100 mbps or less, only 4 conductors are used, the others could be used for power over ethernet or send power over them (ex just send 48v DC or as much as you're comfortable with through the 2 unused pairs, one pair for +v, one for ground) 
You could have one microcontroller with ethernet get buttons state and set leds on/off and get sensor data and push it over the ethernet cable at 10 mbps or 100 mbps and at the other end your device receives it and does stuff with it.
 

NiHaoMike:

--- Quote from: mariush on February 24, 2021, 04:24:26 am ---I imagine ethernet over copper pair (vdsl) converters would work just fine, but they'd be expensive...

--- End quote ---
Or hack a cheap pair of Homeplug adapters, but that sounds like overkill for this application. I would say go with CAN, it's specifically designed to be resistant to noise.

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