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Powering a Flip with a USB cable can be annoying. — Parallax Forums

Powering a Flip with a USB cable can be annoying.

velocityxlrgvelocityxlrg Posts: 18
in Propeller 1
I have a number of Flip boards running off their own wall wart style power supplies (which also powers sensors, etc). The problem occurs when I hook these Flips to a USB hub and then into a laptop to receive telemetry from them. The Flip modules receive power from the usb hub even when the laptop is turn off and when the Flip wall wart power supplies are turned off. So the Flip never turn off unless I remove the USB cables or remove power from the hub. Can the ability of the Flip to run off the USB cable power be disabled?

Comments

  • kwinnkwinn Posts: 8,697
    Sure, you can remove the ferrite bead (FB201) or cut the trace between FB201 and the USB socket if you want to keep the ferrite bead (recommended) to filter out noise from the power supply.
  • velocityxlrgvelocityxlrg Posts: 18
    Thank you!
  • VonSzarvasVonSzarvas Posts: 3,492
    If removing the bead doesn't suit your needs, another option would be to remove D101 (highlighted in the attached image)

    By removing D101, the USB chip (FTDI) will still get power from your PC, and will be able to pass data and operate the tx/rx leds. However, all other circuits will require power from the FLiP 5-9V VIN pin. So the standby current drawn from your USB hub would be really minimal.

    FLIP-Disable_USB_Power_RemoveD101.png
    1994 x 698 - 25K
  • velocityxlrgvelocityxlrg Posts: 18
    Hmm. Removing D101 would cure most of the issues. I guess the down side is that the FTDI chip would be on 24/7.
  • VonSzarvasVonSzarvas Posts: 3,492
    edited 2019-10-30 13:59
    Yes it would- whilst your HUB is putting out power. As you already said, switching off the HUB is one way to deal with this... what about having the wallwart and HUB on the same power switch? Or the laptop and HUB on the same switch, if you don't actually need the HUB when the laptop is switched off ?


    As for the current..... FTDI will take about 8mA in normal operation, plus whatever the tx/rx LED's consume. Probably a couple milliamps when they blink.
    Maybe this is not really an issue to have this running from the HUB when it's left on?
    If you need diagnostic data, then you have no choice but to have the FTDI chip powered anyway!

    If you don't need data connectivity for certain periods, then could you suspend the USB port programmatically? The FTDI datasheet suggests USB Suspend mode current is 125uA
    -- Hold up... if you are powering down the laptop, then the USB port must be getting suspended anyway ?? So is this really an issue- you should only be drawing 125uA once that previously mentioned diode is removed.

    Another option might be to replace FB201 with a switch of some sort, so you can switch on the USB port when you need it.

    Another option could be to check the FTDI CBUS settings in the FLiP, and also refer to the FLiP schematic. Maybe you can achieve what you want by altering the FTDI CBUS settings so that the FTDI chip always goes into suspend mode when the laptop is powered down. (Perhaps first, try un-ticking the option that enables power from a battery charger- that should allow FTDI to auto-suspend when your laptop sleeps)

    There's probably a few ways to solve this- hopefully you find a way that suits your needs exactly.

    Keep us posted on what you try - maybe that will feed some other ideas!


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