Electronic – Does solid/multi-stranded/Litz wire make a difference in binary serial output

serialskin-effectwire

I'm using two shift registers to control 16 digital outputs using only 3 pins on my microcontroller. The parallel outputs carry <= 20 mA DC, their sole purpose is to power LEDs. My microcontroller pins do the following:

  • One is a serial binary data stream (5 or 0 Volts DC). In my case it's a 16 bit periodic pattern which mutates every second.
  • One is the input clock pulse for the shift registers. It sends a HIGH pulse for each bit in the data stream. Depending on how I tune the program, the frequency could be anything from 50 Hz to about 16 MHz.
  • One is the output latch clock pulse for the shift registers. It sends a HIGH pulse for every 16 bits in the data stream.

Does it matter whether I use solid, multi-stranded or Litz wire in this project?

I've read that the main point of Litz wire is to reduce AC resistance at high frequencies. I suppose nothing here really qualifies as AC, and I'll admit the question is mostly academical. But I'm a bit curious since there are some (possibly) high frequencies involved. This formula and these values from Wikipedia give a skin depth of 65 µm for copper at 1 MHz, so the skin effect certainly is significant, at least for true AC.

Best Answer

For all practical purposes, there is no difference between stranded and solid wire. The only exception is for very high speed signals (>1 GHz), where solid is arguably better.

The main purpose of stranded is to make the wire more flexible, and has nothing to do with AC resistance at high frequencies.

There is something called the Skin Effect, where high frequency signals tend to travel on the surface of the wire. But stranded wire behaves as a solid conductor in this regard, because the electrons can travel freely from one strand to another. Litz Wire, on the other hand, has insulation between the individual strands and so does behave better with high frequency signals (how much better is open for argument). I have never seen a commercial product use Litz Wire (ignoring audiophile people). I'm sure there is a practical use for Litz wire, but suffice it to say that it is rare.

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