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Control panel power via USB
Chris:
I am about to redo my control panel with all-USB devices. I'd like to mount a small hub in the panel so I can have a single USB connection back to the computer. What I am trying to decide is if I can get away with an unpowered hub.
The devices on the panel will be:
- A Happ 3" trackball (red boards) interfaced through a Belkin mouse motherboard
- An LED-Wiz driving about 16 LED's drawing 15-20 mA each
- Two Ultimarc U360 joysticks
If I understand properly, if I use a powered hub, I can draw 500 mA from each port on the hub, but if I use an unpowered hub I can only draw 500 mA total. So I'm looking at 250-300 mA worth of LEDs, plus about 50 mA for the mouse board. I'm assuming the joysticks will also draw a max of 50 mA each (similar to the Happ P360's). So I'm looking at 350-400 mA before I take into account the power draw of the LED-Wiz itself and the trackball's optical boards, and of course the power draw from the hub itself.
So, for those more knowledgable than me, my questions are:
- Is drawing the full 500 mA from a single USB port acceptable or am I likely to burn something out?
- None of these are high-speed devices... can I get away with a USB 1.1 hub (if which I have a spare) or do I need to get a 2.0 hub (which I'd have to buy)?
- Is there something I'm not taking into account?
Thanks!
--Chris
stephenp1983:
I'd be interested in knowing this too. I'm running something similar, but less controls in my bartop. I think 9 led's, one u360, and a usb trackball. I was also curious if running any of these through usb 1.1 would cause a problem.
Visitor Q:
I've always found the non-USB powered hubs to work poorly.
MonMotha:
The power situation on USB sadly sucks. Just enough to get in trouble, but not enough to power big loads.
You get 500mA max from the host PC (assuming it's OK with that, which all desktops should be) until you hit a powered hub. A powered hub can usually provide the full 500mA per port, too, but check the ratings on the brick (should be 0.5A * number of ports on the hub). Also, there's a minimum of 100mA per port that has to be reserved for enumeration. This means that an unpowered 4-port hub can only allow a max of 200mA on one port in order to guarantee that 100mA is still available on the other 3 ports.
Also note that you have to "ask" for power when you enumerate. If you just plug in to the power and don't negotiate with the host for more power (and subsequently get approved), you can only "legally" draw 100mA. Some hosts will shut you down if you exceed the limit, but most desktop PCs don't enforce any limits at all other than ~1A for safety reasons. YMMV. I do not know how much power your various devices will "ask" for. Many broken USB devices just ask for the full 500mA even if they don't need it, and as such an unpowered hub will not allow them to start due to lack of available power.
If you must insist on powering everything via USB, the simplest solution is to use a powered hub. If you don't buy the $1 newegg POS special, they tend to work fine. Make sure it displays the appropriate USB IF logo (check http://www.usb.org/ for the logos). Displaying the logo in theory means that the device has been through the compliance verification program though some "foreign" devices ignore the relevant trademark law and display it without authorization. An old hub (USB 1.1 or 2.0 full speed only) should be fine and in fact is probably less likely to be broken than a new cheapie.
I would suggest running power loads (such as LEDs) off a dedicated supply line. This can either be a brick or your PC supply. This eliminates the need to try to power them off of USB.
Kevin Mullins:
Not having all the techy knowledge of the USB hubs.... I can say that I will never use an un-powered hub for anything ever again. You'll find things acting quirky, not working at all, certain things work fine, certain things don't, etc and rack your brain trying to figure out why.
Go with the powered hub.
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