Jimmy said:
I am planning a HTPC systems and need to take USB cable 30-50 ft from the base.
Active USD cable extender are sold at stores but cost too much for my project. I
tested Cat5e at ridiculous length (60 ft and over) and did momentarily get
connected.
I am thinking of make the active cables myself. I can do simple electronics but
so far haven't found any DIY instructions on making an active cable yourself?
Any pointers to instruction over the net? Can't be too difficult since the active
cables sold at stores seem to have only little electronics.
You can get 15 foot active extension cables for $20 or so. They
consist of 15 feet of USB wire, plus a one port hub at the
end. To go 75 feet would cost about $100 or thereabouts.
You could put a powered USB2 hub at the end of the chain,
to provide decent power to the device at the end.
Computer -------- one_port_hub --------- powered_hub ---------- USB_Device
|<--- 5 meters ---> |
|<- $20.00 or so -> |
On Newegg, the reviews for some of the 5 meter active cables,
state they weren't able to cascade them. Some of these things,
only one will work. This one, at least someone got two to work.
It is $11.
http://www.newegg.com/Product/ProductReview.aspx?Item=12-224-004
The maximum total wire length is 30 meters, according to this.
I guess that would be five active cables, plus a passive cable
at the end. The limitation is the number of hubs (which add
significantly to the propagation delay).
http://docs.info.apple.com/article.html?artnum=31116
Using two 5 meter active cables, a 5 meter passive cable,
a powered hub, gives a bit more than 45 feet or so. The last
cable from the powered hub could be up to 5 meters also,
which then covers the 50 foot mark.
The purpose of the powered hub, is to prevent the DC power
coming down the wire, from being an issue. The one port
hub at the end, apparently draws about 5 milliamps, so the
drop in the cable may not affect it. If you had a 500mA
USB_Device at the end of the cable, you want a powered
hub, with its own wall wart, to do the powering.
The above scheme doesn't break any rules, but there could be
some propagation delay and effect on the maximum transfer
rate in megabytes/sec. If a USB hard drive managed 30MB/sec
when plugged directly into the computer, you'd expect
a lesser benchmark with the usage of the additional hubs.
Paul
