My Macbook Pro (13-inch, mid 2009, Intel Core 2 Duo) has an odd problem with the USB ports. Occasionally, when plugging in, removing or restarting a microcontroller such as the Arudino or Teensy, the computer abruptly turns off and restarts. Afterwards, the computer displays a gray screen that says "Your computer restarted because of a problem... etc."

I'm not quite sure if this is related to a problem with my computer, an issue with the microcontrollers drawing too much current or my battery. I know that microcontrollers are sometimes forced to restart if they are asked to source too much current. eg. powering a servo. However, I would expect that a laptop would be able to source enough current to a bare microcontroller to avoid being shut off.

I also should mention that my battery condition is "replace now". I can still use it for ~30 minutes without the power cord, and as far as my memory goes, my computer was always plugged in when this problem occurs.

I read that one problem might be that my PCU might need to be reset. I believe that I reset it using the "SCOP" keyboard shortcut on start-up but the computer gives no indication of this.


A USB port can only typically source 2.5 watts (5 volts at .5 amps). If you are only programming the microcontroller, you should be OK, but if there are any other things the port would be powering (MOSFETs, LEDs, Servos, motors, ... ), and it exceeded the 2.5 watts, you would typically get the "USB Low Power" alert, and not a catastrophic shutdown.

My guess as to what is happening is one of a couple things.

1) The USB port on the MBP is damaged, which can be check by seeing if the problem exists on all other USB ports, or just this one.

2) Verify that all your wiring is correct on the Arduino board. When a microprocessor is reset, it's typical for a pin to be pulled low to initiate the reset. If the board is improperly wired or setup, when the reset happens, one of the USB data lines could be getting 5v applied to it, or the 5v line could be pulled to ground.

3) Electrostatic Discharge could also be causing these problems. I've had microprocessors (connected via USB programmer) reset when touching the metal on my MBP after walking around the office. You may want to consider some ESD mats and bracelets.

  • The problem exists on both of my USB ports. – wyverniv Nov 20 '14 at 5:34
  • The wiring on the Arduino is most likely not the issue since the reset sometimes happens even when only the Arduino is connected to the USB and no other pins are being used. It's good that you mention that the USB port can only source up to 2.5 W at 0.5A. I think the problem most likely lies in drawing too much current and also having a defective battery. Thanks. – wyverniv Nov 20 '14 at 5:39

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