Ardumoto lost direction

Hello,
My first time here in forum, so forgive me rookie mistakes :wink:
I have been playing for about a year with Arduino and electronics, so basics are ok, but still a lot to learn.

Soo, I have this project where I use Ardumoto connected to Uno. I drove one 12V motor. My mistake, I think, is
that I forgot to use Ardumotos Vin connection for 12V power supply. Instead I used just Unos power jack to
power everything.
Something is broken, because motor is going only one direction (it worked ok, two times), when I use 12V power supply connect to power jack.
But, the strange thing is, when I use just USB connection to Uno, everything works (of course a lot slower)?!?!
Question is, any Idea why it works through USB with 5V and not with 12V through power jack?

We need more information about how this motor is wired up and what motor driver you are using.

Yes, basic Ardumoto shield from Sparkfun with L298 chip.
I don't know whether there is many kind of Ardumoto shields?

Anyway, what is confusing, is that it works with 5V through USB and not with 12V power jack.

Logic here: It worked right two times -> lost one direction with 12V-> still works right with USB powered.
I think that it's no matter how it's wired. Something is broke, but what?

Maybe I should learn more about Ardumoto shield, problem should be there....

Anyway, what is confusing, is that it works with 5V through USB and not with 12V power jack.

Sounds to me like you have not wired the Vin to the shield correctly.
You need to supply this with the 12V from the power jack, you can use the Vin pin on the arduino but the current is limited on that pin to about 1A due to the reverse polarity protection diode.
The shield also needs to be powered with 5V for the logic signals.

Thanks Mike!
I agree, that was my mistake. I didn't power it through vin pin and that's how I broke something.

Now I have to study what is broken, Uno or Ardumoto shield. But what gives me headache, is that it now works right with
USB powered and not right with 12V power jack :0

You need to put a meter to it and measure the voltages at various points to see where the USB power and Power Jack power differ.

So is the 5V pin the same under both power inputs? What is the Vin pin voltage, it should be high with the power jack and some what less than 5V with the USB.
What voltage is on the pins of the shield under these two conditions?
Does the rest of the arduino work correctly from the power jack?