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Topic: RS-485 cables (Read 2634 times) previous topic - next topic


Hi everyone,

Can anyone explain to me what an RS-485 cable is? Perhaps in contrast to a standard 22AWG wire I would use with my Arduino pins? I have done quite a bit of reading online and in the forum about it as I have a project that require rs485 communication, but I can't quite seem to get my head around it (or where I am going to find an rs485 wire set).

I have read that cat5 ethernet can suffice as rs485 cable. But how?

This is in regards to the MondoMatrix ServoMatrix board if anyone is familiar with them.

Thanks in advance!


Typically twisted pair wiring is used in this application. A lot depends on the total length the network will span as one can run RS-485 thousands of feet in some applications. In our refinery we ran special low capacitance Belden twisted pair shielded cable for long multi-drop networks that ran to the field plants in rigid conduit and junction boxes. We typically ran 9600 baud and would have as many as a dozen 'drop' on the network.

I suspect you could use nearly any two conductor twisted pair cable if the distance was short enough and/or the baud rate was slow enough. It's mostly about the environment and total length your 'network' has to operate in.




Hi Lefty, thanks for the reply. In my particular application, the network is only a matter of inches (hooking up the arduino to the servomatrix board). Im not sure the baud rate between the two

So do you think a twisted pair of 22awg hookup wires would work for such a short distance? If not, do you know what kind of shops might stock such cables?


For just a few inches at 19.2k baud or less most anything will work fine. Twist together some hookup wire and go for it.


So do you think a twisted pair of 22awg hookup wires would work for such a short distance?

I'm sure it would work fine.


22 AWG is a wire size, RS-485 is an electrical specification.
RS485 is a balanced version of RS232.  That means it has 2 signal wires (same signal, opposite polarity) and a 3rd reference wire.  Typically any noise picked up by one signal wire will also be picked up by the other.  At the receiving end you take the difference between the signal wires and the noise is canceled out.

To use RS485 with a standard arduino you need a converter chip.  I use maxim max485 chips in my projects.  It looks like the ServoMatrix setup has a special arduino board that has the converter.  look at IC3 on the main board.


Thanks for all the responses, starting to understand a little better now.  So RS-485 is a spec and does not refer to the types of wires I use to set up the boards at all then?  The only confusing part to me (not so project-related in my own case, but...) Re: KE7GKP's comments - it seems like a special type of cable would be require at greater distances.  Is this the case? Is the standard RS-485 spec cable usually Cat5?

Thanks for all the help!

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