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Thread: USB Power

  1. #1


    Member Since
    May 31, 2008
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    USB Power
    I have a classroom set up MacBooks. They are the 2.4 GHz Intel Core 2 Duo with 2 GB 667 MHz DDR2 SDRAM.

    I use science probes manufactured by PASCO. The probes are motion detectors that are hooked up to the USB port and draw their power from the USB port. These probes work perfectly on the Mac G4 laptops. They do not, however, work on the new MacBooks unless we get out the MacBook power supplies and plug the laptops in.

    Does anyone have any advice on how to fix this situation. There are simply not enough outlets available to efficiently run this activity without laptops that will power the probes while running on battery power only.

    I sent a note to PASCO and they replied:

    "Thank you for contacting PASCO Teacher Support. Our PASPort sensors are considered "high-power" USB devices and will only work on USB ports that can supply sufficient current. (The motion sensor requires 28 mA of peak power and link requires 2-10 mA.) It appears that the left port on the new Mac books supplies less power than the units on the right port, so I suggest switching USB ports and contacting Apple about the issue. "

  2. #2

    kevindryer39's Avatar
    Member Since
    Aug 17, 2008
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    Specs:
    Mac mini 1.66 GHz Intel Core Duo / 1GB 667 MHz DDR2 SDRAM / 80GB HD
    Unfortunately, the different port issue was intended in the design of the Macbook in order to lengthen battery life. Your PASCO tech happens to be correct in the fact that only one port is meant to be a high-powered port.

    However, it confuses me that according to USB specifications, low-powered devices are supposed to pull a max of 100mA and high-powered devices are supposed to pull up to 500mA and your tech quoted a max of 28mA.

    An easy way to check how much power is being allocated to your USB device(s) is to go open your System Profiler application (Applications -> Utilities). On the left column there should be a category for USB. From there you can see how much power that device is being allocated.

    I know this isn't a definitive answer, but I hope it points you in the right direction

    good luck!
    "I have nothing to say of my working life, only that a [neck]tie is a noose, and inverted though it is, it will hang a man nonetheless if hes not careful."
    --Yann Martel, Life of Pi

  3. #3


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    Thanks. I have a few more questions. First, when I go to system profiler and click USB, I had expected to see two USB ports displayed as my MacBook has two USB ports. Unfortunately, there are 6 or 8 displayed. How do I tell which of these is associated with a specific port I might plug my science probes into.

    Also, is there any way I can send more power to the port?

    Finally, is there any way I can reduce competing draws of power from the port to allow more power to the science probe?

    It seems that there should be some way to change this as the computer automatically sends more power to the science probe when the computer is plugged into the power adapter.

    PS. Is there anything competing with my trackpad that could be disabled. I have often found that my trackpad will have a bit of a delay before it responds to my finger motions.

  4. #4


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    Would turning off Bluetooth have any effect?

  5. #5


    Member Since
    Nov 05, 2008
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    ^ yes i think so....and turn the airport thingy and any other peripherals that you are not using should aid the battery

  6. #6


    Member Since
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    Its not so much a problem with the battery running down, it is that unless the power adapter is connected, the science probes will not function correctly.

  7. #7

    Aptmunich's Avatar
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    Specs:
    Aluminium Macbook 2.4 Ghz 4GB RAM, SSD 24" Samsung Display, iPhone 4, iPad 2
    You can get "y" adapter cables that allow you to combine the power from both USB ports for one device... some portable harddrives include them:

    Amazon.com: USB Power Adapter Y Cable: Electronics

    Perhaps you can source them at newegg or something and buy one for each device.

  8. #8


    Member Since
    May 31, 2008
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    Thanks, if I can't find some way to reserve more power for the probe, I may try this solution. I still can't figure out why a setup that is only supposed to require 35 mA of power has trouble running on either port on this computer. Any ideas?

  9. #9


    Member Since
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    Pasco verified once again that the probes only draw 35 mA of power..

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