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USB Power — Parallax Forums

USB Power

RaymanRayman Posts: 14,162
edited 2007-07-21 15:17 in Propeller 1
Just tested and found that the demo board can run VGA @ 1024x768 with keyboard and mouse attached just off the USB power (i.e., without using the power supply).

I'd really like to run this way all the time, but Parallax didn't provide any easy way to make a nice connection [noparse]:([/noparse].

Ray

Comments

  • BergamotBergamot Posts: 185
    edited 2007-07-18 15:08
    I'm pretty sure a powered USB connection can provide up to half an amp, which is more than enough to run a prop.

    I'm not sure you can get at much of that with the PropPlug/Clip though.
  • Mike GreenMike Green Posts: 23,101
    edited 2007-07-18 16:55
    Bean's "Prop Dongle" is designed to run off USB power. It doesn't come with the VGA and PS/2 connectors or the necessary resistors, but those could be added. See: http://forums.parallax.com/showthread.php?p=653637.
  • RaymanRayman Posts: 14,162
    edited 2007-07-20 20:20
    I've made a simple modification to the Prop Demo board so it is powered by the USB interface.· I've attached some pics...· Pin 1 of the mini-USB receptacle is +5V power.· It looked fairly difficult to get a soldering iron in there, but did see a lead to surface mount cap nearby.· That was simple to solder a jumper to...

    This way, I can take it with me on vacation without the charger!
    UsbPowerMod1.JPG
    1152 x 864 - 539K
    UsbPowerMod2.JPG
    1152 x 864 - 500K
  • Mike GreenMike Green Posts: 23,101
    edited 2007-07-20 21:00
    The major problem with what you've done is that there's no protection against a short circuit. Your laptop or hub's power control circuitry is supposed to protect you from this, but it's always a good idea to put some kind of current limiting in there (like a fuse or self-resetting fuse-like device). There's an output from the USB to serial converter that's even harder to get to that provides 5V with current limiting.
  • Paul BakerPaul Baker Posts: 6,351
    edited 2007-07-20 21:22
    Ray you can use a MF-R025 to protect your board and computer. It is a resettable fuse designed for a 250mA hold current and a trip current of 500mA (which is the maximum allowable current for devices powered by USB), and it's only $0.51, small price to pay for protection.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Paul Baker
    Propeller Applications Engineer

    Parallax, Inc.
  • RaymanRayman Posts: 14,162
    edited 2007-07-20 21:59
    Honestly, I'm not too worried about a short-circuit because I'm not prototyping, just learning the ropes with the VGA, mouse and keyboard drivers.

    Also, I'm fairly certain my laptop won't provide anywhere near 500 mA and will protect itself.

    Still, that fuse does look perfect for this application.· I'll probably get one later...
  • DufferDuffer Posts: 374
    edited 2007-07-21 00:00
    Why not just tap into the USB cable upstream (+5V and GND) and make a "Y" cable using a couple of pieces of wire or cable and a "barrel" jack? Then you could just plug that into the regular power receptacle and the USB cable into the Prop Plug/Clip or Demo board.

    Thats what I do on my Proto boards. USB A to mini B cables are pretty cheap and I always have·old·wall warts around with the right connector that I've forgotten what equipment they go with.

    Steve

    Post Edited (Duffer) : 7/21/2007 12:05:44 AM GMT
  • Paul BakerPaul Baker Posts: 6,351
    edited 2007-07-21 00:21
    That wouldn't work, the input to the barrel must be above 5V, linear regulators require some amount of voltage above the regulated output voltage. Since the first regulator is 5V the input must be greater than that.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Paul Baker
    Propeller Applications Engineer

    Parallax, Inc.
  • hinvhinv Posts: 1,253
    edited 2007-07-21 00:25
    Hi Duffer,

    I would think that if you feed 5v in through the power connector from the USB, you wouldn't get 5v out of the 5v regulator. 3.3 would probably be just fine though.
    To some this matters.

    Rayman, BECAUSE you are prototyping is why you need some sort of fuse protection. Especially if you are using a notebook. They might not have protected it in the notebook as a space saving cut. It would be a real bummer if you blew out on of only probably 3 ports on your notebook. I think Bean has done that allready.

    BTW, Bean, if you are listening....is your Prop Dongle protected?

    Take Care,
    Doug
  • Mike GreenMike Green Posts: 23,101
    edited 2007-07-21 01:15
    Doug,
    Read through Bean's thread on the "Dongle". He did add a self-resetting fuse-like gadget.
  • Franz AchatzFranz Achatz Posts: 140
    edited 2007-07-21 15:17
    my new Propeller board can be powered via USB.
    Works very nice smile.gif


    http://www.xs4all.nl/~achatz/prop11.jpg
    http://www.xs4all.nl/~achatz/prop22.jpg
    http://www.xs4all.nl/~achatz/prop33.jpg
    http://www.xs4all.nl/~achatz/prop44.jpg

    have fun
    Franz
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