Tests to perform after having applied inverse power to Vin?

Using Arduino IDE 1.x
1

Hi,

Yes, I did it, like any good n00b, I managed to connect a 9V battery with inverse polarity to the Vin and Gnd pins of my brand new Arduino Uno (r3).

Funny thing is: it still seems to work fine. When I connected it wrongly, no lights lit up, no smoke appeared, nothing. Since the board gave no sign of life, I thought something was wrong and disconnected the battery. So it has only been connected with inverse polarity for a few seconds. I switched around the polarity and my board lit up like normal, the current sketch running nicely.
Afterwards I uploaded new sketches through the USB (no battery power), played around with it a bit. I even reconnected the battery (the correct way) to make sure it was still working on battery power as well.

So all is well I'd think. But then I got worried and started surfing the web and all I found all over was: "if you reverse polarity, you'll fry stuff for sure" (most likely the voltage regulator and/or some capacitors?). So I was wondering why I didn't seem to have any negative effects and how I could check if my entire board is still working properly.

Based on the info I found so far, I'd say I definitely need to measure the Vin, 5V and 3.3V pins to see what the output is (when I have the 9V battery connected through the power jack, I'll be buying that one today, no more messing around with Vin!). Is this correct? If these values turn out normal, can I safely presume my board is unharmed? Are there any other tests / test sketches I need to try to make sure the processors are unharmed? Perhaps the loopback test as described in the forum here, but as I said, the USB seems to respond just fine.

I could have been lucky that no bad effects appeared so far, but to be honest, that would surprise me. Any info on how to make sure my board is 100% ok would be welcome. Thanks!

2

it still seems to work fine

It's normal : there is a protection diode D1
Have a look on the general schematic or on extract I have done

Alim_uno.pdf (35.3 KB)

3

It's fine. Just don't make it a habit. Especially when you start working with external supplies feeding peripherals.

4

Even without the protection diode the processor can still survive reverse voltage for a short time.
Nothing extra to test.

5

Thanks for your replies! I really appreciate it, as I currently only have a little experience in electronics, from my old days at uni.

It's normal : there is a protection diode D1

I understood from all the sources online that the reverse polarity protection diode D1 was bypassed if you use Vin rather than the power jack? I have located it on the schematic and it does seem to be the case that the Vin goes directly to what I presume is the voltage regulator (U1 NCP117ST50T3G on the schematic), without passing the diode. Am I wrong?

Even without the protection diode the processor can still survive reverse voltage for a short time.

What about the voltage regulator? Or did you mean that one with 'processor'?

I'll feel a little more comfortable after testing the voltages on those three pins tonight, but at least your replies have given me some reassurance. Anyone any personal experience with doing this to the Arduino and it surviving?

6

Yes I have personal experience of connecting reverse voltage to a processor. The regulator is as tough as old boots so that is not likely to be damaged. The only delicate part is the USB to serial chip and you seem to have got away with that.