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Trying to make 2 PORT USB 2.0 Switch

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stevef22

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I am trying to make a USB 2.0 Switch. I want to trade off hard drives inside a DVR. I got the idea from here 2 PORT USB SWITCH

I know I can buy it but I rather find out how to build my own. Anyone seen one of these? I would like to purchase parts from local Radio Shack. I also have express PCB.

This is what I am trying to make, but smaller.


Oh ya, And my USB Switch would have a smaller toggle switch, maybe a rocker. Probally couldn't use LED Rocker switch because those require 12v. I don't know what I can tap off of inside this DVR.

Thanks for your help and ideas!
 
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Sceadwian

Banned
USB 2.0? That's a toughy, the signal is very high frequency so normal switch connections are likely to have way too much parasitic capacitance to use. Maybe a solid state analog switch? Not sure the bandwidth they're capable of but USB 2.0 is up to 480mbit's, USB uses some slightly fuzzy encoding methods but acording to the wiki entry bandwidth on a true high speed USB devices is between 20 and 200mhz.
 

stevef22

New Member
Thanks for those specs. How did you know that? Did you find that on the spec sheet I linked. I am trying to learn everything about USB 2.0. Ive heard that USB 1.0 and 2.0 are only different in software. The Hardware is the same. Is this true?

Thanks you
 

Sceadwian

Banned
USB 1 and 2 are the same? Of course not. Full speed USB 1.x data transmit speed is only 12mbit, about one and a half megabytes (raw data protocol overhead not considered) Full speed USB 2.0 is 480mbits or sixty megabytes (again raw data) obviously this is a big difference in speed. The hardware is relativly similar, the clock rate is just massivly different. All USB 2.0 devices START communication using USB 1.0 speeds (just in case) and then go through a reset phase which restarts them in 2.0 mode once the system acknowledges compatability.
 

Sceadwian

Banned
I used babelfish to translate that web page and it states USB 2.0 is not supported.
 

stevef22

New Member
I know they are not the same, I just thought the difference was in the software/protocol, not in the hardware. Good idea to translate that page! I emailed the author of the page at both his emails and haven't received a response yet. I asked him if he is working on a manual USB switch. I noticed a driver was supplied with the plans for that device. Very cool however.

Any USB Gurus out there?

PS> I ordered that switch I posted originally. I want to take it apart and also learn from it. I will update on progress.
 

Sceadwian

Banned
If you're going to use a manual switch why don't you just unplug it from one and into the other in the first place? That's only slightly more complicated than turning a dial.
 

stevef22

New Member
I am trying to hide the hard drive inside the dvr. Having a rocker switch on the outside would clean it up nicely. I plan to run the switched data to a pc.
 

tkbits

Member
stevef22 said:
I know they are not the same, I just thought the difference was in the software/protocol, not in the hardware.
There's a difference between USB 2.0 compatibility and functionality.
A device that uses only USB 1.1 signals may be compatible (and will subsequently be advertised as USB 2.0 compatible), but it won't handle the high speed 480 Mbps mode.

The high speed mode of USB 2.0 uses different voltage levels than the two USB 1.1 modes (supported by USB 2.0). It is also a true differential signal with the idle mode being 0V difference between the two data lines, rather than one line high and one line low of USB 1.1.
 

Super_voip

New Member
Just getting back to the original concept, why you need a USB switch. The harddrive in the PVR/DVR won't be USB? Most are IDE and only look for a HD with the master switch set.
 
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