dockingstation -> USB question...

**porto** · 08-20-2010, 08:58 PM

Hello,

I'm busy with a dock for my Mac Mini 2.0Ghz. The Mac will not permanently settle in the car but is has to be removed overnight.

The Mac got 4 USB inputs and that's my question about:

I'm in doubt in using all 4 inputs or just 1 input and connect all my (7) devices through a self-powered USB hub; the latter gives less cables and less trouble with the dock itself (multiple in/out shoving of the Mac, connector not straight in line after some time etc etc.).
I know a selfpowered Hub can handle multiple host powered devices but I'm not sure how much mA the touchscreen will suck, the external soundcard, the external microphone etc.

Here is my devices list, all are host-powered:

1. GPS mouse
2. Keyboard/keypad
3. Display (touchscreen)
4. Soundcard (Hercules Muse XL pocketLT 3)
5. Silabs Radio stick (yet in doubt, probably use Internet Radio instead)
6. Usb hub (2nd, non-powered... for connecting cardreader, memstick)
7. Andrea USB-SA Mic (for cellular phone)

Personally I want to go for the 1 USB input with a selfpowered Hub because of the more reliability when moving the Mac in and out every day, but if this will certainly give problems with the above devices requiring too many current from the Hub I will reconsider.

Please your advise.

Porto

**soundman98** · 08-20-2010, 10:17 PM

i know that some have run into problems running some devices through a hub, so you might want to experiment first with all the devices first.

primarily, you might want to consider at least keeping the monitor on a second plug, so you can still control the pc if your hub were to go bad..

for power, usb specs say that any single usb port cannot output any more then 500mA, so it is usually easiest to get a rough estimate of power requirements by adding up devices assuming that they pull the full 500mA from each port... this is not completely realistic for most devices, but will give you some overhead for power as well...

also, if you haven't seen it yet, check out bugbyte's old install, he had also created a docking solution for a mac mini in his car..

**porto** · 08-21-2010, 10:02 AM

Hello Soundman98,

so 500mA is the limit per port/device on a selfpowered hub?
That of the monitor connecting to a dedicated port is something I didn't thought of, I will do that guaranteed.

Within windows I can't seem to get info of the current mA need of a specific USB device.
I just found out I can get that info within Mac OsX, which is also installed on my Mac Mini (duh!). The Muse XL soundcard draws the full 500mA. Only drawback is that a device must be recognized first by OsX before he shows me the info of that particular device; so it's driver hunting season for me now!

Thanks! Porto

EDIT: I looked at Bugbyte's thread about installing his Mac Mini but, unfortunately, the thread is quite old so all the install pictures are already offline.

**Chronus72488** · 08-22-2010, 03:43 PM

500 mA is the limit on ANY USB port, self or host powered. Host powered USB hubs split the power of that port into the amount of things that are plugged into that hub. For example, given an iPhone 3G, WiFi Adapter and Bluetooth Adapter were plugged into a single host-powered hub, that hub would provide 166.67 mA to each port (500 mA / 3 ports) but it really needs to provide 1.5 A (500 mA * 3 ports = 1500 mA = 1.5 A) since they are all high-speed devices.

Self-powered is the way to go for what you are trying to do, that way each port will get it's own dedicated power supply and not have to fight for it through a host-powered hub. But like Soundman said, take 500 mA and multiply it by how many ports you need to use, and supply only that much power to the hub, otherwise you'll be looking for the fire extinguisher sometime soon =P