FTDI/Serial cable, safe to leave connected?

Store Forums RGB Matrix Backpack General Discussion FTDI/Serial cable, safe to leave connected?

This topic contains 3 replies, has 2 voices, and was last updated by  Michael 5 years, 12 months ago.

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  • #660

    hobs
    Member

    Hello,
    I just built the backpack and works great, thank you!

    Is it safe to leave the FTDI serial cable connected to an USB port when the display is powered and running?
    I have noticed that if I plug the USB the backpack *and the display* are powered from the usb port (yuck!)

    Should I disconnect the 5V from the FTDI header?

    thank you
    Hobs

    #1802

    Michael
    Keymaster

    You can leave the FTDI USB cable connected to the backpack+display ONLY if you are providing 5V power from the power adapter. You can’t power the backpack+display with USB alone (as you found). Make sense?

    #1803

    hobs
    Member

    Um, yes, I was more concerned that in that case, am I not basically powering the USB port, and possibly the entire +5V inside the host, which in my case would be a raspberry pi, plus its own power supply, with a non current limited source? (I don’t think there’s a diode or a pptc, fuse or any kind of protection anywhere, i am just putting the two supplies in parallel, right?)

    Just noobie doubts, thank you.
    H.

    #1804

    Michael
    Keymaster

    The USB port on the Raspberry Pi is at 5V. When you connect a power source to the backpack using a power adapter, that also sets the 5V line on the FTDI cable to 5V. So both the Pi and the backpack are setting this line at 5V, which is fine. No current flows because they are at the same voltage. If you unplug the Raspberry Pi, then there could be current flowing into the Pi, depending on the design of the USB on the Pi, but it probably has a diode in there somewhere. Having all this connected and powered at the same time is fine, but don’t remove power from either the backpack or the Pi.

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