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I'm going to use ethernet cable as a long range cable for serial (5v) and power (5V and 16V, almost no A) and I remember reading that because of the loops in the wire and the impedance effect some pairs were best for data and others for power. I doubt it would make much a difference for my case, but i'm still curious :)

I'm searching the heck of it but can't find anything useful on that end.

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They do have some differences in the pitch (the amount of twists per distance,) however this is to help prevent cross-talk between the pairs by making sure the same conductors of the different pairs don't repeatedly lie next to each other over the entire length of the wire.

Green and Blue are the most twisted then orange and finally Brown is twisted the least.

You need to use each twisted pair with its polar opposite. Normally each pair carries a differential signal so that any interference is cancelled at the receiver, but I'm not sure exactly how you're going to be using it.

For example, the blue and blue stripe should be +5v and -5v (or ground.) This will help to cancel noise and help to reduce the cable from producing noise that may interfere with something else.

I remember reading that because of the loops in the wire and the impedance effect some pairs were best for data and others for power.

It is best practice to use the blue and green pairs for data and the brown for power. You can also use the orange for power, especially if you are pulling a bit of amperage. You can couple the orange and brow solids together and the orange and brown stripes together.

Be careful to not use to long of a run and make sure the device powering the serial can provide enough power or else you may damage you device.

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Ethernet cable is made of several twisted pairs. As I remember, the pairs have the same base color: Blue/white with blue, Brown/white with brown, etc. Each pair is identical in term of impedance. In order to avoid problems with your serial communication, especially if it's long range, you should consider transforming your standard serial link to a differential one. Consider using a EIA RS-485 transceiver. the RS-485 norm defines the physical layer and other stuffs, but not the protocol you have to use. Thus simply transforming your 0-5V serial signal to a RS485 using a transceiver will work perfectly. And you will have much less trouble with electrical disturbance. By the way, never use an output of a microcontroller such as an UART output to feed a long running cable. It's not meant for that. The impedance is probably not correct for that usage, and the port doesn't contain enough protections. Without proper external protection or correct cable usage, a lightning strike nearby could destroy your microcontroller port.

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