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USB interface question.

I'm newbie at USB, if someone can help it would be wonderful:

I'm envisioning a gadget that would take input from a USB port on a PC (or any USB host). And it would act as a UPS for four downstream USB devices, providing currents upto 1A.

In other words, the gadget would have 4 USB sockets for output, capable of providing upto 1A to devices connected to it.

I have done some reading on USB but would like to ascertain whether the gadget needs to have a controller / or can it be a passive device, as far as the USB interface circuitry is concerned ?

(of course, the gadget would have its own separate supply, from where it will derive the UPS power)

-Mike

Reply to
siliconmike
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"siliconmike" schreef in bericht news: snipped-for-privacy@c74g2000cwc.googlegroups.com...

Mike,

Buy a simple externally powered USB-hub. The ones I have simply connect the

5V to their power outputs, so they pass all of the current the power supply can provide to the USB-devices. I even saw some (older) PCs that has connected their 5V power directly to the USB. (Way beyond spec and risky of course.)

petrus bitbyter

Reply to
petrus bitbyter

Well, any USB hub with a wall wart would do this. The only problem is that

1A is far beyond the USB specs. Any device is not allowed to consume more than 100mA from the start and after negotiation with the host, it may consume up to 500mA. If you draw more, you'll get a "USB overcurrent" message. This means that a hub can measure the current of each port and shuts down a port that is loaded to heavy.

Meindert

Reply to
Meindert Sprang

The gadget I mentioned is part of a bigger project. I mentioned it separately only to simplify conversation.

-Can I just short the D+ pin from input to output ports

-Then short the D- pin from input to output ports

-Provide a separate 5V VBUS+ to output port

-Provide a common shorted GND.

Or is this a disaster eh? Mike

Reply to
siliconmike

Yes, the electronics world be a simpler place, if everyone followed the specs correctly ;)

Reply to
siliconmike

Ahhh you just need a powered hub - like the one I bought 4 years ago

David

silic> I'm newbie at USB, if someone can help it would be wonderful:

Reply to
quietguy

Start at the beginning. UPS, is a _point to point_ interface. There can only be one USB device on a 'leg'. To have multiple USB devices from one host, requires a hub. Now other people have then pointed out that 1A, is more power than the target device is allowed to draw off USB. 0.5A max, and even this requires negotiation (though a hell of a lot of hubs, will supply this power without comment). You could potentially use two USB sockets, and draw 0.5A off each, but realistically, the simplest solution, will be a seperate power connection for the devices. However it actually sounds as if the devices will be normal USB units, in which case you might as well reduce your power capabilities to 0.5A each...

Best Wishes

Reply to
Roger Hamlett

"siliconmike" schreef in bericht news: snipped-for-privacy@j55g2000cwa.googlegroups.com...

Mike,

USB connectors are designed to make and break contacts in the right order. The hub I think about has its own 5V (wall wart) power supply that has been connected to the 5V power pins of the output directly. So the USB hub can provide whatever current its power supply provides... as long as the conductors and connectors can handle it. Which, of course, comes with its own risks. A short in one of the connected (USB)devices may fry the internal organs of your hub and damage other connected devices as well.

IMHO this scheme is a consequence of a free interpretation of the specs. The USB host should be able to provide 100mA at first contact and possibly 500mA after negotiation. If you interprete these values as *at least* 100mA and

*at least* 500mA respectively, you can possibly use even a 100A power supply. No need to say it's little bit beyond the maximum current your USB cables can handle ;)

petrus bitbyter

Reply to
petrus bitbyter

And is there a way to make this hub a CPU-less device?

Or are there available hub ICs to minimize homework ?

Thanks Mike

Reply to
siliconmike

Any number of hub IC's. Alcor, FTDI, Atmel (AT43301), Cypress, NEC, Philips, SMSC, TI (most of their's have some extra functions built in)....

Best Wishes

Reply to
Roger Hamlett

"siliconmike" schreef in bericht news: snipped-for-privacy@m38g2000cwc.googlegroups.com...

Yes, the ones I talked about are made that way.

Yes, the hubs a talked about contain one of these.

petrus bitbyter

Reply to
petrus bitbyter

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