8/8/8 board connection problems on active usb-hub

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g-e-c-o

8/8/8 board connection problems on active usb-hub

Postby g-e-c-o » Mon Jan 19, 2009 8:18 am

I've got an active usb-hub with the 8/8/8 board and other devices connected.

The board changes it's state from offline to online and back in a 1-2 second period.
Nothing is connected to the board. When I disconnect some devices from the usb-hub the change from offline to online state of the board gets longer.
If I disconnect all devices the board keeps staying in online state.

I have measured the current that the board takes, witch was way under 100mA.
The usb-hub is powered with a ps that could give up to 7-8A.
I also changed the usb-hub, that didn't help.

Why doesn't the board keeps stable in online state??
Could it be that the board requires more than 5V from the usb-port??
Can I connect the board to 12V to make it stable?

Please help!

fitchett
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Postby fitchett » Mon Jan 19, 2009 12:15 pm

It sounds like you are right on the edge of operational USB voltage (4.6 volts absolute minimum)

Your USB hub is probably getting 5 volts, and dropping 0.4V in it's internal regulation?

Can you measure the voltage the 888 is getting? You can measure the voltage at an analog input.

Chester

g-e-c-o

Postby g-e-c-o » Tue Jan 20, 2009 1:48 am

Looks like the voltage drops to 4,72. Connecting a passive hub to the active hub of the where the 888 is also connected to the voltage even drops to 4,69! Already critical?

If I connect instead of the passive an active hub the voltage stays stable at 4,72.

The problem could be my ps witch sholud give 5 volts. After 4m I only get 4,85 volts out of the cable. And this is the place where my hub gets it's power from. So maybe that long cable cuses all the problems?....

fitchett
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Posts: 263
Joined: Fri Dec 05, 2003 3:45 pm
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Postby fitchett » Tue Jan 20, 2009 10:22 am

Unfortunately, most hubs do a really cheap job of implementing power management. You really should have a hub that can put out 5V+. Perhaps you can do that by providing 5.25V to your hub.

Chester


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