Hi guys just want to know if any have an idea of what happened or what caused this.
I plugged my arduino into my laptop, it didnt want to go on so I hooked up my 12v battery which I have hook up plenty to my Uno through the power jack and (just smoke ) seems to me that thing on top of the board next to the power jack fried .
Regarding the usb power seems my laptop needed a restart because my mouse didnt want to work either.
Thanks...............
that thing on top of the board next to the power jack fried
That would be the voltage regulator. Did the smoke come from the voltage regulator? Did you hook up the 12V power to it with reversed polarity? This will fry the voltage regulator quickly. Have you hooked it back up via the USB connector to see if the board powers up since then?
I fried a voltage regulator this way once on a MEGA 2560, but the board would still run when powered from the USB connector; I replaced the voltage regulator and the board works just like new.
{:0)
Brandon
Okay, so you plugged it into your computer.
It was shorted, and pulled down the +5v on the USB (probably tripping a polyfuse), that's why your mouse stopped working.
What you should have done at that point is be like "omg" and unplug it, and get out your ohm meter and find the short.
Unfortunately, your response was instead to plug in a larger power adapter which could supply enough power for the arduino to fry itself. That was not a good thing to do. Unless you're up for some surface mount rework, you're probably gonna need to buy a new arduino board.
Hi Brandon thanks.
Just tested it via usb, it still works it seems that just the voltage regulator fried.
I really dont think I hooked the polarity up wrong , I mean i did check before I connected the battery and my motor driver was also connected at the same time and that still goes on(dont know if it works but the lights go on).
An arduino can handle 12v right, The battery was standing outside maybe a bit in the sun, could that cause a voltage spike?
I also normally connect the motor driver first and then only do I put the switch on to turn the arduino on.
This time the switch was on when I connected the battery so both went on at the same time.
Drazzy how am i supposed to now about a polyfuse etc haha but I do now thanks.
If it still works off USB, you probably didn't hook up the polarity backwards (assuming it's an uno, or other board with the same power management - the opamp usually dies under reverse polarity, becoming a short)
I think you had power and ground touching somewhere (could even be conductive debris on the table), so when you connected the external adapter, tons of current flowed, so the regulator got really hot and started smoking.
12v should be fine for Arduino, though if you're pulling a lot of current, the regulator will overheat (remember the definition of a watt, and consider that the regulator is dropping 7 volts)
Ye my power jack is cracked a bit maybe it shorted there cant think of any other place it could short.
Will the regulator still work, dont want to plug it in again if its gonna smoke.
No current draw is in the miliamp area so that should be fine, well gonna see if I can fix the power jack and see if that helps.
Thanks Drazzy
Undermentioned:
Hi Brandon thanks.I also normally connect the motor driver first and then only do I put the switch on to turn the arduino on.
This time the switch was on when I connected the battery so both went on at the same time.
It sounds like you had a short .
high current drain will cause the regulator to fail due to overheating
Hi,
What size is the 12V battery?
Do you have a fuse in its lead?
You say you have used the 12V battery before, this quite high for the internal reg to drop to 5V if you are powering a lot of things off the arduino's 5V pin.
I use 9V as my supply to help keep heat dissipation down.
Tom.... 
If you connected the motor shield before you connected the power you could have latched up the arduino. This causes in effect a short on the board which will blow your fuse.
But you said you did it the other way round, which is right.
Hi Tom
The battery is a 12v 32amph, Ye the only reason im using it is because my motors need the big battery and powering everything off one power supply is just easier.
Ive got 3 HC-Sr04, Rf receiver and the motor driver that draws power of of the arduino, but the motor driver has its own supply directly from the battery as well.
And no I dont have a fuse on the leads.
But yes Ive used the battery connected like below plenty.
Yes Mike I normally plug the lead into the battery which is directly connected to the motor driver, then once thats connected I put the switch on to power the arduino, but didnt see the switch was on this time when I connected the battery .
Well everything works fine(via usb) now except I cant power it externally, I must of had a short somewhere, could a short in the power jack cause this or did everything just draw to much current all at once and why this time?
Thanks chaps
If there was a short on the 5V line shouldn't the regulator just shut down ?
If you short your 5V pin to GND would it normally fry the regulator so fast ?
I think it would. Assuming a 12V input, if your power supply can supply a good current, that'll be several watts dissipated in the regulator and a really fast increasing temperature.
My point is those kinds of regulators have fold back current limiting. If if shuts down it shouldn't be dissipating maximum power. If it were NOT a short , but something that draws 1 A I would agree with you
but a dead short should cause it to shut down completely.
Provided it has foldback limiting.
OP has not said where arduino came from.
Other thing is foldback can fail if it is not mounted on a large enough heatsink
Indeed, I don't really know how these foldback are reliable but I won't really count on them 
Guys I got an old pc here I can take a part, there are 2 regulators here a niko p3055ld and a niko p3055ls im not really understanding there datasheets, will either of them work?
Thanks
I found the short I hooked up the motor driver power that it gets from the arduino the wrong way round so the 5v was on gnd and vice versa.
Idiot all these wires get confusing for me sometimes.
Idiot all these wires get confusing for me sometimes.
We all make mistakes but does this scenario sound familiar ?
I witnessed this once when I
was using a 12V, 10A P.S. (because it was the only 12V supply I had with me) to power a 555 timer circuit
and accidently shorted the output pin of the chip. It popped with a bang, started smoking, glowed red, and
ignited the plastic case of the chip and burst into flames.
The moral of the story is when you use a p.s. capable of delivering a lot of current , you have to use a fuse
in series with the power supply , otherwise , if something goes wrong , all that power is available to destroy
anything downstream. The Catch-22 is that if your load requires 2A, you can't use a fuse less than that so
you have to be extra careful how you wire things up. When I am working on circuits with a lot of wires I get
small adhesive labels and label all of them just to be safe. Lesson learned.
What's the damage ?
Ye raschemmel I reckon im going to label them all as well and yes that fuse is a problem because the motors will need about 30A if under load if not they normally run around 10A each so 20A is needed for them both.
Luckly its only the power regulator that burned, Im trying to find a replacement from stuff at home because I stay on a farm not close to any shop so with shipping and all its expensive for it haha
Although my power splits of to the arduino so could put a 1A fuse there .
I would suggest ordering a replacement and waiting.
You could damage the reg by unsoldering even if its suitable.
then damage arduino further by re soldering.
If its working off usb leave it at that until new arrives.
S@@t happens as they say.