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I'm trying to use a Dell mouse and keyboard via a single USB port using the USB splitter hub, but the devices seem to misbehave. Just one of the devices work when I connect both. I figured out it's a power issue. But, generally, the output of a USB port must be maximum 500mA and my mouse only needs 100mA, and the keyboard, 50mA at most. So, I assumed that both should work.

I checked the voltages using the multimeter and the result was this: voltage of other 3 ports in my 4 port hub drops to 0.81 volts as soon as I plug in any device. The current output was maximum 0.18~ 0.2 Amperes. Is there a problem with my USB port (it's a USB 3.0 port)?

  • BASIC TROUBLESHOOTING. Try the hub on another machine. By the way, how are you checking the voltage with a mutlimeter? where are you putting the probes? normally with usb i'd have thought it isn't exposed. – barlop Jun 15 '14 at 6:02
  • Hey barlop ! . Yes, the connectivity leads aren't exposed in a usb . I used a usb connector and took wire leads to check the voltage. As for vcc and gnd, I saw the pin diagram. – Haresh K Miriyala Jun 16 '14 at 11:47
  • ok..also as amps are done in circuit.what method did you use there? by the way there are devices that do it ebay.co.uk/itm/like/310979647177 Really the way to figure out if a part is at fault,is to try it on different machines with different devices, and isolate the problem that way.See if you get a voltage drop on another computer.See if u get a voltage drop with another usb hub(they are dead cheap).It is dead easy to troubleshoot 'cos there are computers all over the place, and usb hub,keyboard,mouse are cheap and easy to try different ones.And u have a GR8 test(the voltage drop) – barlop Jun 16 '14 at 13:42
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USB standard expects 5V ±5%. That's 4.75V to 5.25V to be valid. Between the Hub IC, the Keyboard and Mouse, something is bringing the voltage down enough for it not to work. Measure the current and voltage from the Upstream port, and see what it is.

That said, I've had more (flash drive, wireless mouse, keyboard) on a cheap 1 dollar usb hub and it worked. Have you tried a different hub?

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Almost no desktop that I know of only has a single USB port - so is this a tablet, laptop or other form factor? Reason I'm asking is that you could try plugging the devices into different ports to see if they work.

Also, since you are using USB, Bluetooth jams USB 3. If you are using BT, try and turn it off and test.

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  • "Bluetooth jams USB 3" I googled that and got 0 useful results. Could you explain that one!? How can wireless bluetooth "jam" a wired connection? I use bluetooth and USB 3 together with no issues. – Bort Apr 1 '16 at 2:11
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    There have been MANY documented cases where wireless signals cause issues with wired USB 3 connections. Search for bluetooth usb 3 interference and you will find links to Intel, Apple, and other major manufacturers that have seen this issue. Seems that the harmonic from 2.4Gig wireless devices (including WiFi and BT) sometimes get into the USB cables (and vice versa). Shielding and other methods of attenuation are recommended. One example: intel.com/content/www/us/en/io/universal-serial-bus/… – Blackbeagle Apr 1 '16 at 4:06
  • @Blackbeagle you info is wrong. At least you read your reference wrong. It says USB3 will interference the 2.4GHz radio not other way around. So basically the USB3 signal can block the BT/WiFi if the USB3 cable is too close. 2.4GHz radio cannot jam USB3. Their power is far lower than USB3. – Wang Nov 24 '19 at 21:03
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I read you need to use a 2.0 USB hub and not a 3.0 USB hub in order to get a keyboard & mouse to both work through one USB hub.

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    That would defeat the purpose of USB 3.0 hubs. – gronostaj Mar 31 '16 at 20:41
  • Any reference for that statement? (Where did you read it?) – Arjan Mar 31 '16 at 20:46
  • please add your source – conquistador Apr 1 '16 at 12:24
  • USB3 chips contain USB2 hub by default – Wang Nov 24 '19 at 21:05

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