What could I have just cooked?

Using Arduino Installation & Troubleshooting
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I have been running an Arduino Uno with a EasyDriver to drive a stepper motor, power supply for this was from a 12Vdc 1A mains supply and everything was fine.

This morning I removed the main supply and used a 12V Car Battery and something inside my project box cooked as there was lots of smoke pouring out so I quickly pulled the supply off but no nothing seems to work.

If I plug in the USB lead the UNO lights come on and if I run the Serial monitor then I can see all the usual debug information showing all the switches works etc.

If I plug in the main supply then the UNO come on and the EasyDriver LED comes on but even though the UNO serial monitor works ok there is no action from the stepper motor.

Do you think it it the UNO or EasyDriver that has cooked. A am leading towards the EasyDriver as the UNO serial monitor does work but would like a little nod if there is a way to check either.

Also, why would it cook the XXXXX when using a Car Battery as my power source?

Thanks

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A am leading towards the EasyDriver as the UNO serial monitor does work but would like a little nod if there is a way to check either.

Using a multimeter you can check the 3V3 and 5V supplies to make sure they are working. You can also use a LED (with current limiting resistor) to check each out of the I/O pins. Without doing some testing it is difficult to say what is or isn't broken. However, your current assessment seems correct.

Also, why would it cook the XXXXX when using a Car Battery as my power source?

The car battery provided significantly more current than your 12V supply. Your 12V supply had a current limit (or capacity) of 1A. It probably provided more. The car battery is capable of suppling significantly more current (10s of Amps).

Are you sure you did not connect the Car Battery backwards? The Uno has a diode to help protect in reverse voltage conditions. The other board probably did not.

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Thanks James for the Advice, I am a novice when it comes to electronics and here in the UK none of the local colleges do electronics course's. Plenty of basket weaving and do wired complementary therapies though!.. I degress.

I shall do what you have suggested and it won't take long to do these and upload some code.

With your suggestion about the car battery connected backwards, I have a positive 2.1mm power jack fitted that plugs into other bit of equipment so reverse poliarty is not a problem there though I did check to make sure.

I have ordered a new EasyDriver as it is only 8GBP here in the UK as I have just noticed that one of the pins (pin 20 Load Supply 1)on the Allegro A3967 driver chip is blackened after checking the board with a magnafying glass.

Pin 20 is the fifth pin from the top left one the piccy above.

To prevent this from happening again, is it as easy as you say about putting in a capacitor in between the supply input connector on my breadboard and the EasyDriver PWR In (top right) to only allow say 1A to pass (not sure if that is right as I just don't know)

Thanks for your help James

PS, on just checking to let you know, the EasyDriver PWR IN can take 7 to 30V and has a 47uf capacitor fitted which is the big round thing on the right marked 47 VZA

The circuit diagram I followed to build the stepper motor is http://4.bp.blogspot.com/_POxG6aoXG3o/TAsyGBniZBI/AAAAAAAABLQ/X6nFqJ1TOAg/s1600/ED4_revised.jpg expect I replaced his 12v .4A regulated supply in his diagram with a 12v 1A regulated supply to test and then I used the 12v car battery when I had no access to mains in the shed. That's when it smoked

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