I need to make a communication between only two devices with a distance of 5 meters, which are connected by a cable of 4x2.5mm² (see in the image), being 1 wire for GND and wire for 12v, that would pass nominal current lower than 10A, and the other two wires will be for communication. I thought to use rs485, would it be possible to use 4 way cable without being twisted for a 5 meter distance and slow speed rate (1 byte every 50ms at most)? Would you have any other suggestions? Thanks in advance.


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    \$\begingroup\$ Although rs485 is better for long distance, 5 meters it not that a long distance. You can easily do standard RS232 over 5 meters. The drivers for that are a bit easier to obtain. I don't now what you are trying to do but how about a run-of-the-mill USB cable with RSR232 at the end? It also has power (but not 10A) and signalling. \$\endgroup\$
    – Oldfart
    Commented May 12, 2019 at 5:38
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    \$\begingroup\$ It depends how noisy the 10A is on what needs to be done. \$\endgroup\$ Commented May 12, 2019 at 6:10
  • \$\begingroup\$ Check out the LIN bus (you can run your normal UART using LIN transceivers, you don't have to follow the LIN protocol itself). Should do fine in this scenario. \$\endgroup\$
    – filo
    Commented May 12, 2019 at 6:44
  • \$\begingroup\$ Unidirectional or bidirectional? \$\endgroup\$
    – CL.
    Commented May 12, 2019 at 8:24
  • \$\begingroup\$ If each receiver has 1 millisecond low pass filter to remove most noise (100 ohms, 10uF ceramic), or a 160Hz LPF, with hysteresis such as 74LS14 or modern equivalent, this datalink may be simple. Depends on the ground-currents and the ground-spikes between the 2 systems. That may upset the bits. \$\endgroup\$ Commented May 12, 2019 at 11:09

1 Answer 1


The TIA-485 standard does not specify what kind of cable you have to use for RS-485 networks. Twisted pair is very frequently used because it's cheap and works very well for most scenarios.

For your particular application I would say it depends on how noisy your power supply and loads are but at such a low speed unless you have to deal with a horribly noisy environment you should be good.

I would like at it from a different angle though: you're wasting quite a lot of copper there. But I guess 5 meters is not that long, but you might consider replacing your four-wire with a two-wire for power plus a twisted pair that would be probably cheaper and lighter.

If you are asking for a theoretical development of this problem a very good reference is this one: Noise Reduction Techniques in Electronic Systems by H.W. Ott. In there you will find the how and why of the twisted pair.

Another good reference to look at is: Serial Port Complete by J. Axelson. This book will give you a lot of tips on the practical side of RS485.


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