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propstick usb and usb power? — Parallax Forums

propstick usb and usb power?

henry99henry99 Posts: 67
edited 2009-07-26 16:55 in Propeller 1
Sorry if this has been asked before but has anyone tried just jumping pin 1 of the usb port (+5V) to the +3.3 Regulator input?

The usb port is supposed to be able to handle out 500mA.

Or am I missing something?· I'm not sure why parallax didn't include this as a power option.

Comments

  • TimmooreTimmoore Posts: 1,031
    edited 2009-07-26 08:26
    Its been talked about a number of times and a number of us do this without problem. Its not clear why Parallax haven't done this, the common assumption is that you are meant to report the power taken from USB to the USB host and its not obvious how much power will be taken since you can add stuff to the boards.
  • RaymanRayman Posts: 14,844
    edited 2009-07-26 14:54
    I think they're worried about beginners damaging their computer and then blaming Parallax...

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    My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm
  • Mike GreenMike Green Posts: 23,101
    edited 2009-07-26 14:56
    The main problem is that the USB spec is very restrictive. You can only draw up to 100mA until your device is enumerated and notifies the host that it will need to draw up to 500mA, then you can't draw more than that. That kind of behavior would require additional circuitry that only a few people would use. Those devices that Parallax does have that use USB power draw well under the 100mA limit.
  • RaymanRayman Posts: 14,844
    edited 2009-07-26 16:55
    Mike, I think all the Parallax USB devices use the FTDI chips, which can negotiate the power requirements with the host...

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm
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