Arduino fried macbook

I'm a TA for an intro to engineering class and one of my students was programming his arduino with his macbook.

He had the gate of an nmos transistor hooked up to pin 11 and the negative end of a 14.4 volt battery hooked up to one of the ground pins. The positive lead of the battery was not attached to anything yet. He also had the arduino plugged in to the usb port of his computer at the time. He says he looked up at the circuit to double check before uploading a new sketch to the board, and when he looked down, his laptop had turned off.

The arduino's ATmega328 was slightly more than warm to the touch and his macbook would not turn back on. The battery on the laptop is fully charged.

My guess is the battery sank -14.8V and fried the arduino and usb port in the process, effectively ruining something on the mobo of the laptop.

Anyone have any ideas before I tell him to buy another arduino, contact apple care, and hope he isn't out a laptop?

If the macbook doesn't reboot after all is disconnected there may be serious damage. Can be anything but I think the powersupply is the first suspect. Don't know if the macbook has a fuse that can be changed. Otherwise it's time for apple repair man.

The Arduino can be tested just with the led blinking sketch from another PC or Mac. But replacing an Arduino is relatively cheap ...

There should be a fuse on the usb port and a fuse on the Arduino. At worst he should just have a dead usb port and a dead Arduino. Good time to teach them not to work while it's powered though.

The more-than-warm ATmega328 is not a good sign. It suggests it was either sourcing/sinking too much current or, despite the protests of your student, was driven by -14.4V.

Unfortunately the fuse on the USB power line is not enough. With -14.4V applied it is possible the AVR fried, which in turn took out the FT232 device, which in turn allowed 14.4V (or -14.4V) to appear on the USB D+ and D- lines, perhaps even the +5V line which the fuse is supposed to protect, but as a thermal device it takes a "long" time to do its thing (where "long" is relative to the time it takes to destroy electronics that don't expect 14.4V applied).

-- The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, light sensor, potentiometers, pushbuttons

I guess I should also note that when the arduino is taken off the usb port and hooked up to a 9V battery, the LED on the board attached to pin 13 (pin "L") remains on constantly and the green "Power" LED lights up as well, but again, the chip gets warm rather quickly

The positive lead of the battery was not attached to anything yet.

I would say that the evidence (non-functioning MAC and non-functioning and hot Arduino) is that is a untrue statement. Treat the problem as if the 14 volt battery got wired to the Arduino and USB +5vdc power buss. That means major repairs and troublshooting lies ahead, sorry. The thermo fuse on the Arduino protects the PC from over current situations but not overvoltage situations, it's not fast enough for that level of PC protection.

Lefty