Trying to extend USB while balancing cost with performance

I have an electronics box with a Mega in it and it needs to transmit duplex between the box and a USB receptacle for a PC some 15' away. Oh and there's a 380VAC 3-phase supply in between so lots of EMI.

My solution to the distance/noise problem was to use an AOC (Active Optical Cable) USB cable that converts the signal to light and back again at the other end. However I "may" have a dilemma with this approach.

The AOC cables are exclusively 3.0/3.1 standards... least the ones I found that were humanely priced. Now I'm not sure if the serial chip on the mega puts out USB 1.1 or 2.0 but I would assume it's 1.1. Some of the incidental literature I've come across while shopping for the cable has insinuated that USB 3.0 isn't backwards compatible with 1.1. I'm not sure if it's the cable their talking about, the data stream or both.

So I start out at my Mega in the electrical box and I want to send it out through the AOC but do I need some sort of dongle coming right from the Mega to change the signal to something 3.0 compatible and then plug the AOC into that or how does it work? If the only thing on the other end is a cheapo crappy USB extension going to a PC with 2.0 or less support, is THAT going to be a problem too?

Just trying to understand the USB standard better and how it may cause a problem for transmission between the Mega and the PC when a 3.0 cable bridges the gap.


USB 3 allows communication at a faster rate than earlier standards. All USB standards automatically work with the lower speed categories.

Just plug it in!

Really? So the AOC can plug right into the arduino and the other end, to a PC and it will work with no issues? Why did I think it would be a problem? Now I'm checking to see where I saw compatibility issues with 3.0.

It is part of the specification that higher USB grades work with the lower. If it does not, it is not compliant with USB. :roll_eyes:

So either it is , or it is not. :grinning:

It seems you're right. I guess it is that simple. I need a vacation.


I have a question, I was under the impression that AOC cables provide ground isolation and not EMC immunity (necessarily). You might check the cables, I doubt they are USB-Optical at each end with only fiber in the middle. I could be wrong as I've never used isolation devices in a cable.

How fast do you need to go?


Glass/Light is not vulnerable to EMI so if the construction is fiber optics, then it should be immune. Of course at each end the signal has to be converted to electrical again so those points would be vulnerable but at least you don't have 50' acting as an antenna. This is my understanding anyway.