USB reverse switch - 1 client, 2 hosts

[Xyz123]

I wish to build this using a 74HC4066 switch. My main application is a USB harddrive storage that would be switched between two computers.

Several anecdotes:

1. should I only switch Data-, Data+ or should I also switch Vcc?
2. should there be a delay between switch off (of host X) and switch on (of host Y), or can I switch the wires simultaniously using an inverter?

 

[iso9001]

You are just looking to switch them so you don't have to unplug the wire each time right ? Not trying to use 2 active hosts or anything like that right ?

USB can drive upto 450mA if I remember right (I'm probably wrong on that, but its pretty high up there).

So that rules out a few digital SPST switches. Maybe mechanical switches or solid state relays ?

Maybe MOSFETS ? I just learned all about low On Resistance mosfets, you could get tricky with them,

Having just reaseched digital switches myself, and if you are going to stay in spec, 450mA is going to be a pain.

Thats about all I can help with,
good luck

 

[Xyz123]

Thank you for your post but this doesn't help at all.


* "Not trying to use 2 active hosts or anything like that right ?" - no

* "USB can drive upto 450mA" - pls refer to **broken link removed**


i just need to figure out:

1. can the USB Vcc of host X be directly wired to USB Vcc of host Y
2. should there be a delay before client-host X cut off and client-host Y switch-on.

 

[Nigel Goodwin]

i just need to figure out:

1. can the USB Vcc of host X be directly wired to USB Vcc of host Y

No, you will probably damage something!.

2. should there be a delay before client-host X cut off and client-host Y switch-on.

I would expect so.

 

[Xyz123]

but why... wiring USB Vcc's of two hosts togeter... what could possibly happan?

 

[Nigel Goodwin]

but why... wiring USB Vcc's of two hosts togeter... what could possibly happan?

Wiring two voltage outputs together is NOT a good thing, they won't be EXACTLY the same voltage, and one will draw current from the other.

Basically, in almost all circuits, you can wire multiple inputs to one output, but NOT multiple outputs together - unless it's designed specifically to do so, using open collector or similar.

 

[suicidalmonkey]

I think you need to consider the data transfer rate of USB (480 megabits per second).

I think making a switch yourself would create too much 'noise' and could corrupt data.

 

[Xyz123]

Wiring two voltage outputs together is NOT a good thing, they won't be EXACTLY the same voltage, and one will draw current from the other.

i guess i'll have to switch both data-, data+ AND Vcc.

is it ok to assume i don't have to switch GND?

Basically, in almost all circuits, you can wire multiple inputs to one output, but NOT multiple outputs together

Pls explain the corellation of input and output to my case

I think you need to consider the data transfer rate of USB (480 megabits per second).

Why? i'm gonna use a chip based switch, not a mechanical one.

Thank's to all!

 

[Nigel Goodwin]

Wiring two voltage outputs together is NOT a good thing, they won't be EXACTLY the same voltage, and one will draw current from the other.

i guess i'll have to switch both data-, data+ AND Vcc.

is it ok to assume i don't have to switch GND?

Correct!.

Basically, in almost all circuits, you can wire multiple inputs to one output, but NOT multiple outputs together

Pls explain the corellation of input and output to my case

Vcc is an output from the PC!, as you're connecting one device to two PC's you mustn't join them together.

I think you need to consider the data transfer rate of USB (480 megabits per second).

Why? i'm gonna use a chip based switch, not a mechanical one.

Which is why you need to ensure the chip will handle such a high transfer rate (assuming you're talking USB2 and not USB1?).

 

[bloody-orc]

i suggest just swich all the pins. then there is no problem with all this stuff... there aint so much of those pins you know. also for swiching you must use something that can handle 500mA minimum. maybe not for the data pins but for Vcc it is essential cause this little ******* draws the most of it. it has motors inside them and those aint gonna run on the amps that most digital IC's can suply. check the swich datasheet and see if it can do the Vcc swiching of will it burn in flames. when not then just put a transistor/relay/mosfet in the output nad swich the Vcc using this. (relay would be the choice of mine). also i suggest not swichit douring data transfer. it aint gonna do the Hard Drive and PC any good.


PS" Grounds MUST be connected when you chose not to swich all the pins.

 

[William At MyBlueRoom]

If you simply want to share a USB drive between 2 computers a linksys nlsu would do. Of course you need ethernet, but it's cheap and common.

**broken link removed**