08-05-2014 07:56 PM
We need to control about 6 or 7 usb 6008s or 6009s. We have a few of each. The DAQs will not turn on when plugged into the usb hub we are using. I have tried different computers (both quite old and running Windows XP however), and also different ports of course. The hub ports are rated to 500mA each, while the DAQs typical draw is 80mA with a max of 500mA so power should be the issue. I've also tried two different usb hubs and am getting the same results. There have been points in time where the setup has worked, but after powering down there is no guarentee it will work again. When the DAQs are plugged directly into the computer and working, the green light they have will flash half on half off (50% duty cycle), but when plugged into the port and not working, sometimes the light will blink on then off really fast, like a 5% duty cycle. I am unsure of what that may be indicating. Could the DAQs not be getting enough power or is this just due to old computers? Should DAQs not run on hubs? I don't see an alternative to using a hub if that is the case though.
08-06-2014 09:39 PM - edited 08-06-2014 09:41 PM
I suspect that power is the issue. Six devices will use all of the available power from your hub, if they do not draw more than the typical amount. 6*80 mA = 480 mA. 7*80 mA = 560 mA > 500 mA. Although not specified it is not unreasonable to expect that the current requirement might be higher during initialization. While each port may be rated for 500 mA, the total for the hub might also be limited.
Can you run 4 or 5 reliably on your hub?
The manual does not specify a rapid, low duty cycle LED mode so that may also point to a power problem.
Search for Jeff Bohrer's FAQ on USB power issues. An external hub with a robust power source is often a good choice when multiple USB devices are required.
Lynn
08-18-2014 09:35 AM
Yeah all kinds of problems with this. Don't get me wrong USB hubs can be used on DAQ hardware, but don't be surprised if it stops working. Powered hubs are more likely to work, because they don't just draw power from the one USB port of the PC, but still I've had issues with powered hubs.
The best solution is to get USB PCI cards for the computer, and dedicate as many DAQ devices to these ports as possible. Use hubs for slow devices like mouse and keyboard.
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08-18-2014 09:45 AM
Hooovahh wrote:
The best solution is to get USB PCI cards for the computer, and dedicate as many DAQ devices to these ports as possible. Use hubs for slow devices like mouse and keyboard.
The best solution would be to go to a PCI(e) device that has enough IO for your application. So much more reliable. I avoid USB at all costs in my test systems because USB is nothing but trouble for a dedicated system.
08-18-2014 10:07 AM
@crossrulz wrote:
Hooovahh wrote:
The best solution is to get USB PCI cards for the computer, and dedicate as many DAQ devices to these ports as possible. Use hubs for slow devices like mouse and keyboard.
The best solution would be to go to a PCI(e) device that has enough IO for your application. So much more reliable. I avoid USB at all costs in my test systems because USB is nothing but trouble for a dedicated system.
Yeah okay I guess if you can get away with it. But I assume the poster already has this USB DAQ devices and wasn't looking to get other DAQ hardware.
I too try to stick with dedicated hardware when possible. I remember seeing a tester someone made that I needed to assist on that had 9 of these cheap USB CAN devices. They had that plugged into 3 USB hubs, that then ran into a 4th USB hub. So a total of 13 devices, down to one PC port. Surprisingly it didn't just crash and burn, but only failed under parts of the test that were high throughput. I helped them re-design it with a MXI PC card, to a cheap PXI chassis with MXI built in. It cost more sure, but was more robust, and actually worked.
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08-18-2014 12:03 PM
We ended up buying a higher quality hub for about $40. Sometime the computer will loose the connection to one of the DAQs and we have to restart the LabVIEW program, but it is working for the most part at least. We will try a PCI card though if need be. Thanks.
08-18-2014 12:54 PM - edited 08-18-2014 12:57 PM
+1 for power and a decent USB hub.
Spend the money on a good USB hub. Lately I've been using Startech's 4-port and 7-port hubs with good success. Far better than the cheap consumer-grade stuff, without the excessive cost of the Moxa offerings. Other nice thing with the Startech hubs, inside them is a pair of jumpers that allows you to enable/disable self-power and bus-power modes.
Another thing, in Windows Device Manager, go through all the 'Generic USB Hub' and 'USB Root Hub' and uncheck "allow the computer to turn off this device to save power". All that does is cause problems.
6008 in each one of these, one 7-port hub per board, two boards into one computer.
Lotsa DAQs.