Arduino Fried By Its Own Power?

First, check the schematic here: http://cl.ly/0Q070w0v3g2F3f3H0A3Q (this is EVERYTHING connected at that point). It was connected to an Ethernet Shield on the Uno.

Basically I had GND on one end of a 470k/1M voltage divider and I was using an analogRead() to measure the voltage of the battery (which had its + terminal DISCONNECTED at the time of the incident) using the middle point of the divider and doing the math in code. I wired the Arduino’s +5V pin to the end of the voltage divider to test to make sure my code was giving the proper output.

The instant I connected +5 (the wire shown in the schematic as a dashed line) the MacBook Pro powering the Arduino via USB INSTANTANEOUSLY shut down. I confirmed afterward that BOTH USB ports are perfectly fine (no damage to them).

Immediately I disconnected the +5V wire and the USB cable and carefully studied all my connections to ensure I hadn’t missed something. Once I had written down the schematic, I took the Ethernet shield off and plugged the Arduino back into the USB port to check it. The ATMega began to heat up dramatically, clearly fried. Here are the chips I’ve confirmed heat up abnormally when plugged into USB:

  1. ATMega328
  2. ATMega8U2
  3. LM358 Op-Amp (the one to the left of the crystal when viewed with the USB port on top)

The Ethernet Shield attached to it appears to be fine; I need to test it thoroughly to be sure though.

What would cause this to happen? There were no abnormally high voltages attached, and current wouldn’t have been an issue through those high resistor values. I’m completely baffled here.

EDIT: Probably obvious by now, but the serial port for the Uno no longer shows up in the Arduino software. Our other Uno still shows up and works fine (further proving my USB ports are still OK but that the board is fried).

(Attachment below is the same as the file linked to at the top of this post).

Fried.pdf (28.3 KB)

As the drawing is written and the sequence you discribed there is no way to have damaged the board. The most likely situation is that the circuit is/was not as you have drawn or the sequence was actually different and you somehow applied my mistake +12vdc to either the arduino AO pin or the arduino +5vdc pin. As the board shut down I suspect you got +12vdc connected to the arduino/usb +5vdc power bus.

That's not what you probably want to hear, but the fact that the two active semiconductor chips (the 8u2 chip and the 328p are now hot to the touch and nothing functioning, I can think of no other logical failure mechanism.

Lefty

Thanks for the reply. That was my immediate thought when it happened, but the battery had nothing connected to the + terminal, just one wire from -. I went over it thoroughly and what's on the schematic is 100% correct...

jfm429: Thanks for the reply. That was my immediate thought when it happened, but the battery had nothing connected to the + terminal, just one wire from -. I went over it thoroughly and what's on the schematic is 100% correct...

Well then the Arduino Gods must have struck the board down for some past sin you commited. ;)

Lefty

Heh… so far I think that’s the only explanation. :smiley: A friend of mine who works a lot with Arduinos is stumped as well. That’s exactly why I can’t figure this one out, there’s nothing I can see electrically wrong with the circuit, and I know for certain there were no wiring discrepancies.

That and the fact that it also shut down my computer (not like a normal shutdown; it was an instant full power down) but everything is perfectly fine with it. I don’t know where that fits in.

I did notice, though, that the board that fried has a PCB that has a greenish tinge to it, whereas the other one is a deeper blue, which I would think probably indicates they came from different manufacturing batches. Just an observation…

That and the fact that it also shut down my computer (not like a normal shutdown; it was an instant full power down) but everything is perfectly fine with it. I don't know where that fits in.

PCs normally have protection on their USB ports for external faults due to external electrical faults. The Arduino also has a on-board 500ma thermofuse to protect the PC from excess current draw from the PC USB port and so a short circuit on the arduino's +5vdc bus would not normally effect the PC. However having +12vdc somehow shorted to the arduino +5vdc would create a situation of reverse current flow to the PC and is probably what shutdown your PC and cooked your arduino board.

So while you may not be able to recreate the situation in your mind, all evidence points to you somehow getting your +12vdc crossed onto your arduino's +5vdc power.