USB Power Question

Hi there!

I'm currently doing the touchscreen and bluetooth mod for my aa1 and have reached a cross-roads.

I've bought a 4-port hub and am wondering whether to:

a) Solder both TS and BT to it.

or

b) Solder the TS to the miniPCI-X USB and solder the hub (with connected BT) to the other USB pad underneath the HDD. I've read that the hub will receive 500mA from the 1 USB port and each of the 4 child USB ports on the hub can only address 100mA each.

Wikipedia: "A bus-powered hub is initialized at 1 unit load and transitions to 5 unit loads after hub configuration is obtained. Any device connected to the hub will draw 1 unit load regardless of the current draw of devices connected to other ports of the hub (i.e 1 device connected on a 4 port hub will only draw 1 unit load despite the fact that 5 unit loads are being supplied to the hub)."

Therefore I'm worried that wiring both devices to the hub will mean either they don't get the power they require or I can't further add devices (in the future) to the 2 spare ports because of power constraints.

But the other thing is I want to minimise the amount of soldering I do onto the mobo as I'm not pro.

Help!
Matt

 

The USB port should be able to supply 500mA. The BT adapter will use less than 100mA (possibly much less) and although I don't know how much a touchscreen uses, I would be astonished if it used > 400mA. Most USB devices without heating/lighting elements or moving parts don't use much power so unless you are intending to attach a HDD or a light, you should be fine with the hub.

 

"The power consumption of the hub controller(including touch + usb hub) is about 120 mA"

Source: viewtopic.php?f=43&t=286&p=41941&hilit=touchscreen+power#p41941

I'm just wondering how other people (who have done BT + TS) have gone about this.

Another source on USB:

"USB current (directly related to power) is allocated in units of 100mA up to a maximum total of 500mA per port. Therefore a compliant bus powered hub can have no more than four downstream ports and cannot offer more than four 100mA units of current in total to downstream devices (since one unit is needed for the hub itself). If more units of current are required by a device than can be supplied by the port it is plugged into, the operating system usually reports this to the user."