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Parallax Propeller Plug - knocks out USB scanner — Parallax Forums

Parallax Propeller Plug - knocks out USB scanner

groinksangroinksan Posts: 3
in General Discussion
I have a strange situation going on with my set-up.... I have a Propeller Plug, and it works great.

I have a Windows 10-based laptop. I've attached a USB2 hub, and I have a USB scanner, UPS and wireless mouse dongle attached to the hub. I'm using the hub because the laptop itself is hard to reach from my workbench.

When I attach the plug onto the USB2 hub, it knocks out the scanner. The scanner basically keeps disconnecting/connecting every second infinity. I remove the plug, and the scanner re-mounts and all is good. I have two of these plugs, and both of them causes the same problem. I don't have a problem with the UPS or the wireless mouse - both are functional just fine.

Of course, the fix is to connect the plug to a different USB bus. But purely for philosophical and intellectual reasons, I'd like to understand what would cause the scanner to react like this with the plug connected?

Aloha!

Comments

  • Ron CzapalaRon Czapala Posts: 2,418
    Is it a powered USB hub? The Propeller plug draws power thru the USB port - it might draw more than the HUB can support.

    If you right click a HUB in Device Manager and click the Power tab you can see the total power available (per port) and power required for attached devices.

    This is from Windows 7:

    USB%20HUB%20POWER.JPG
    USB HUB POWER.JPG
    425 x 470 - 44K
  • groinksangroinksan Posts: 3
    Didn't think much about the hub itself. The hub is not powered. I wasn't able to find the hub in Device Manager. Instead, I have a USB power meter that can fit between the laptop and the hub. I connected the hub to the laptop naked, and alone it was pulling 0A at 5.01VDC. With the three devices connected to the hub, everything was pulling 200mA, and the voltage was about 4.98VDC. When I added the Plug to the mix, the power went down to 4.95VDC, and the scanner started going nuts. So I'm sure it is the hub. I'm just amazed at how much power the Plug draws.
  • msrobotsmsrobots Posts: 3,704
    @groinksan,

    first of all, welcome to the forums.

    The USB-Standard allows the Host to vary the provided mA per port, and allows Devices to ask for some mA. So the voltage drop you see is insufficient supply.

    That is the reason for powered USB-Hubs, because one can attach up to 127(?) devices on one USB-bus. Theoretically.

    you left out the mA number after connecting the PropPlug. Could you just connect the PropPlug and measure the mA it uses?

    just curious,

    Mike
  • localrogerlocalroger Posts: 3,451
    The PropPlug's power draw is pretty close to the rounding error for zero; my USB voltage/current monitor puts it at zero even though it can resolve 10 milliamps. And this makes sense, as the FTDI chip shouldn't really need much current to power it.
  • groinksangroinksan Posts: 3
    Using the USB voltage/amp meter, the Plug is pulling zero amps. I'm assuming the amount is too small for the meter to pick up. These meters aren't the most reliable.
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