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Thread: SheevaPlug butchering

  1. #1
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    SheevaPlug butchering

    I want to get my SheevaPlug working properly in my car.

    There's two things I really need for this; first, I need to change the power supply. Second, I need to be able to plug at least two USB devices into the plug [GPS puck and OBDII dongle]. Ideally I would like to also be able to run wifi and/or bluetooth dongles in future.

    I have one of these things [I bought it a while ago]: dynex 4-port hub that I've taken apart. There wasn't a power supply in the box, but it has a power plug on the side. On the bottom, it says it takes 5V power at up to 2.5A. I'm not sure if I can actually use this to do what I want - any suggestions? Taken apart, it's very small and will easily fit inside the sheeva alongside the PSU

    I'm looking at buying one of these carnetix devices: CNX-P5V, which someone else has already used to power a sheeva.

    Can I safely/correctly/whatever use these two devices?

    My vague intention is to shove the PSU inside the sheeva but off to one side, then put the usb hub in there too.
    Second, desolder the current power plug from the usb hub and desolder the usb port from the sheeva motherboard
    Finally, attach the usb cable from the hub directly to the sheeva mainboard, and power from the P5V to the hub.

    Intuitively I anticipate problems with just attaching the sheeva and the usb hub to the P5V in parallel, but I don't know if I'm just mentally manufacturing problems. I have tried attaching the hub to the sheeva, but without extra power it wasn't sufficient to run my GPS puck, let alone work with the OBDII dongle too.

    I'm also a total coward; my car is still brand new [ish], and I'm not ready or willing to drill holes on it or solder stuff in it. It has a 12V cigarette lighter in the back that I never use, so I was thinking of plugging the whole ensemble into that. It'll magically power up when the car turns on, and power down when I turn it off. Is that reasonable? [I have a mini cooper S. If anyone knows of any other non-invasive ways to safely run power from {wherever} to {within reach}, I'm very open to suggestion]

    I've kinda crossed out of my realm of experience here, so I'd appreciate any suggestions or general direction-pointing.

    Thanks,
    Gary (-;

    PS Oh, yeah, the other problem is that I'm cheap; I don't really want to buy expensive parts if it's not entirely entirely necessary...
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  2. #2
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    Of course, ideally my dream device is some kind of combined USB hub and 5V power supply combined into one convenient bundle. I looked, but I don't see anything like this.

    At CES, I talked briefly with Rob and he mentioned the existence of such a beast, which could be used with powersupply-less sheevaplugs, if they ever got manufactured. Erm, can anyone point me in the right direction on that front?

    Gary (-;
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  3. #3
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    I'm also looking at powering a 5V usb hub and my plug with my USBDCDC PSU from minibox. I'm also afraid of the consequences of messing with the mysterious power of electricity in this regard.

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    That tutorial looks competent... and you should have no issues powering your USB in parallel to the sheeva off the 5v output of the Carnetix power regulator as long as the USB hub does not have a regulator inside of it. I look forward to seeing your progress with this, and perhaps I might wind up buying my own sheeva and doing this
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    There is this, which may not quite fit inside the Sheeva case but is made for 12v operations. I tested it and it has worked without flaw. Pricey, though.
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    Yeah, I was looking at that. The problem was that it doesn't seem to have a 5V supply rail to use with the plug, just the USB devices. I've ordered the P5V and will see what to do once it arrives.

    Gary (-;
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  7. #7
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    I just hooked up my 5V USB hub to my DCDCUSB thingy in parallel with my sheeva. I will power on tonight and let you know if it works. my hub is also 5v @2.3A.
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  8. #8
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    Okay if you follow what I did in my guide for changing the power supply in the sheeva, you'll have all the power you'll need. You won't even need to get the hub its own power.

    Right now, I have a 4 port hub plugged into the USB port. On that hub, I have a verizon 3G stick, the fusion brain, a pen drive, GPS, and a bluetooth dongle. Been running this way since august.

    Your biggest issue is going to be cooling the thing. I put a heat sink on the regulator and took it out of the sheeva plug because it was getting above 110 degrees in there. If you want to keep everything in the plug, consider adding a small fan.
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    OK, So, a full writeup will be on the way, but I wanted to throw some numbers out there. I have, indeed, rewired my plug with a Carnetix P5V. I kept the USB hub external, but I ran a power cable from the PSU to outside the plug so I can power the external hub [or, optionally, remove the hub]. Photographs are on the way, but some numbers:

    1) I measured the temperature of the un-heatsinked PSU to be 65C/149F. Holy hell, paul wasn't kidding that that would be a problem.

    I have a roll of 12g copper wire, I'm thinking I'll make a short piece of that and run it directly from the screw on the PSU to the 2600 pound heatsink it's going to live in... somewhere. For reasons you're about to see, I don't really want to add a fan.

    2) Power! Keep in mind that I attached my ammeter between on the very input-most end of the electricities inside the plug, so we're at 12V. That means that 1/2A is 6 Watts of power. I have a fairly cheap multimeter, so when it comes to amps above 200mA, I only get two decimal places.

    .51A - Plug on, USB hub plugged into the USB and power. GPS [BU353 puck] and OBDII [OBDPro USB] plugged in and actively sampling [This is my intended final setup]
    .48A - Same getup, with the GPS puck unplugged [BU353 => 30mA. Awesome]
    .36A - Same as .48A, but after running "shutdown -h now". Indeed: After turning the OS off in the plug, it's still sucking more than 4W
    .29A - Still shutdown, now with the USB completely removed [unplug the hub from the USB port, and pull the power plug from the USB hub]
    .21A - Pulled the ethernet cord out. Apparently just being plugged into the ethernets draws three times as much power as my GPS puck, even while the OS is down.

    As you might reasonably expect, pulling the SD card from the slot had no measurable effect.

    So, there you have it; after powering down the OS and unplugging *everything* except the power, the plug was still sucking 2.5W, and while cranked up with everything I want, it draws 6W.

    I took pictures as I went and I'll be posting them sooner or later, but I just wanted to post my immediate findings on power-related things since it seems pretty interesting.

    Gary (-;
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  10. #10
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    According to the Carnetix Documention on the topic of heat:
    2.3.1 Heat Dissipation of the Regulator IC

    The P5V can be used as a stand-alone (not installed inside a P1900/P2140) Point of Load (POL) regulator for powering +5V devices. When using the P5V as a stand-alone POL you will need to make sure there is adequate heat dissipation for the regulator IC. If your connected +5V devices consume
    less than 1 amp the P5V can operate without a heat sink. However, if your +5V devices consume greater than 1 amp you will need to attach a heat sink to the mounting tab of the regulator IC. You can either use a small, finned heatsink such as the Aavid/Thermalloy 530613b00000 shown here. This type of heatsink is available from companies such as Radio Shack (276-1363) and DigiKey (HS320-ND).

    Other heatsinks can be used as long as they are rated for 16degC/W or better (lower). This heatsink will allow the P5V to operate at maximum power (3 amps) at an ambient temperature of 60degC. The heatsink will become very hot to the touch at maximum load. Please be careful not to touch it or let it come in contact with plastic or flammable materials.
    Gary (-;
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