Accidentally Powered Using USB +12V

I was making a USB supply cable and accidentally powered the USB with +12V. Now the Arduino UNO is not detected on Windows in the device manager.

Does this mean it is hosed?

The UNO schematic shows a fuse at the USB input. But as the electronics blows quicker, I don’t like your chances.

Weedpharma

Normally the delicate electronics blows first to protect the inexpensive fuse.

MorganS: Normally the delicate electronics blows first to protect the inexpensive fuse.

Why do you think the Arduino doesn't have a 5.6v zener from USBVCC to ground? Isn't that the normal design to shunt the extra voltage off if it occurs, cause a large current flow, and give the PTC fuse time to clamp down? They put that PTC there so they know there is a hazard at that point, why not add the diode?

Costs an extra 10 cents per board maybe?

Weedpharma

The don't put a Zener because you would have to include a seriese resistor to drop the load and that would interfere with normal operation.

Anyway it is quite hard to "accedently" connect 12V to the USB power anyone who manages to do so deserved to have their Arduino trashed.

OK now, two things.

Firstly, the polyfuse takes some time to reset, so if you tried to operate it immediately after the accident, it might still be OK - just wait a few hours.

Secondly, recognition of the USB function indicates function of the ATmega16U2 and has nothing to do with the ATmega328. If you had the "blink" sketch loaded and on powering correctly, it blinks, the ATmega328 may still be OK.

12V will almost certainly destroy most of the chips on the board in a matter of microseconds, you don't expect to survive that level of overvoltage as the MOSFET gate oxide will breakdown.

MarkT: 12V will almost certainly destroy most of the chips on the board in a matter of microseconds, you don't expect to survive that level of overvoltage as the MOSFET gate oxide will breakdown.

Am I reading the schematic wrong? It looks like USBVCC goes directly to the Atmel USB front-end uC and a regulator. It doesn't go directly anywhere else. The regulator should be able to survive that. The Atmel IC maybe not.

If you blow the USB interface chip you'll not have a USB interface, making programming tricky!

BASIC RULES OF ELECTRONICS 1. Is it switched off? 2. Is the voltage correct? 3. Is the polarity correct? 4. Redo above check! 5. NEVER CONNECT ACTIVE COMPONENTS!

Always use a digital LED Voltage Readout on your PSU.

Print this out and place in front of you on your work station.

MarkT:
If you blow the USB interface chip you’ll not have a USB interface, making programming tricky!

Essentially what I was saying.

Kudos to Sploddy!

Another rule:

A wire cut to length will be too short.

Weedpharma

On the contrary I find that cut wires are often too long. You try to cut them shorter and then one will be too short, then they go back to being too long again.

MarkT: If you blow the USB interface chip you'll not have a USB interface, making programming tricky!

There is an ISP header on there. Go ahead and buy an Atmel programmer. :)