Take your USB devices to far away places

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Product: USB Active Repeater Cable
Company: Micro Innovations
Price: $18.99

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EVERYONE AGREES that today's USB devices are nice. But there are hurdles, specially if you want to place USB peripherals far away from your computer. In this article I'll show you there is a special type of USB device designed to address that problem. Anyone who lived the golden era of SCSI peripherals - back when it was about the only solution to hook up fast external devices- must remember the headaches of "bus termination", the expensive adapters for the half a dozen different scsi connectors, and short cable lengths. In that sense, USB saved us all from cable hell... for a short time. I recently hit the most famous limitation of SCSI once again, but this time with the USB bus: cable length.

WinXP fails to recognize a peripheral plugged using a cable that is too long.

According to the USB FAQ, the USB's design does not allow cables longer than 5m and 3m (full speed and low speed, respectively): "When USB was designed, a decision was made to handle the propagation of electromagnetic fields on USB data lines in a way that limited the maximum length of a USB cable to something in the range of four metres.

This method has a number of advantages and, since USB is intended for a desktop environment, the range limitations were deemed acceptable". Acceptable for committees, yes, but not for me. I had a very specific need, and it was to place a USB webcam looking out from one of my windows. That involved drilling holes through brick walls between the room where the webcam is and my "data room" where the host PC is sitting, and then laying out plastic "wire ducts" with several turns to reach the drilled holes. This increased the wire length two-fold compared to the straight line cable path.

When I measured the total distance, it turned out that I needed one USB cable about 15 metres long -around 49 feet-. Not knowing the 3-metre limit of "low speed" usb devices, I simply thought of getting enough "A-A" USB extension cables and chaining those together to achieve the desired total length. The normal extension cables are dubbed "A-A" because they feature male and female versions of the "A" plug that inserts on a PC, allowing it be chained to another cable or usb peripheral with "A" plug. Those cables are inexpensive; you can buy a 12 feet extension cable for around $6 greenbacks. If you fall into this mistake like me, you'll happily return home with several a-a extension cables in hand, plug one after the other, until you finally reach your USB device (in my case, the webcam). But such joy will vanish quickly, as you find out there's a limit on how far USB signals can go. Yes, the USB FAQ was right.

When I plugged the long set of cables into my Win2k PC, Windows 2000 greeted me with a message that read something like " USB Device @#$!.+as@##)(@!? [gibberish] detected". When I repeated the experiment on a system with WinXP, I found that this windows version at least hides the gibberish, but shows a window saying there's a problem with the device. Clearly, some of the data was being lost along the way, and there was no way to configure or make the USB device work. It was clear: I needed a way to boost the USB signals along the way, preferably inside the wire ducts.

When cheap A-A extension cables fail to work, it's time to get a USB repeater

I repeat, a repeater
The USB FAQ offers a "solution" that is not very elegant or in some cases feasible: "buy a bunch of hubs and connect them serially with 5m cables. If you need to go farther than that, put another PC, or maybe a laptop, out where you need the device to be and network it with the first PC". Yeah, right.

Micro Innovations' USB Repeater

Luckily a google search informed me of USB repeaters. However, finding one locally down here in South America was as difficult as finding Condi Rice fans. A USB what? was the usual response I got. And placing USB hubs along the way was not very practical. As usual, Amazon.com came to the rescue. I ended up purchasing Micro Innovation's "USB Repeater Cable". Unlike a "USB hub" which needs to be recognized/configured by the OS the first time you insert it or when you decide to plug it into a different port, and in many cases powered by an external power supply, this one takes power from the same USB bus and acts as a "transparent repeater", that is, it boosts electrical signals on the USB cable, without showing up as a device on the usb bus at all.

USB Repeater again, packaged.

Inside the beast

The Topshine TH2000 USB repeater chip inside

While you might think that boosting signals in an usb bus is trivial, it is not. There's a chip inside this tiny box that does all the work, and takes power from the same USB bus (no power supply needed). The TH2000 "usb repeater controller" chip comes from Taiwan based silicon firm Topshine Electronics Corp. An HTML version of the chip specs can be found here. One of the things you learn is that only USB 1.x is supported, but seriously... are you going to place your external DVD burner or USB 2.0 hard drive at the other side of your house or flat?

The packaging says that you can "chain up to five of these units for a total cable length of 80 feet". However, spending on several units might not be even required, so experiment before getting half a dozen units. I was able to chain a SINGLE usb repeater cable connected to three regular 9-feet (A-A) usb extension cables -one before the unit and two after it-, and my webcam has been working flawlessly (knock on wood) ever since. Without the active USB repeater in the middle, the device wouldn't even be recognized by the PC due to the signal loss as shown in the images above.

The verdict

Micro Innovation's repeater is a very capable and simple product at an affordable price. It's totally transparent to the software side: No drivers to install, no "recognition" needed by the OS, you just plug it and works. The only downside I can find on it is that it currently doesn't support USB 2.0 "full speed" just USB 1.x speeds. But as far as I know, the only devices currently making use of 2.0 speeds are storage devices or scanners that most people would prefer to have near the PC, not far from it. Keeping that in mind, it's a very nice product. I give it Five Fernandos in my personal one-to-five rating scale. If you want to take your USB devices to far away places, it's a must. µ