I tried wiring up a new L9110 motor controller to my Uno. It worked fine using the 5V and GND pins from the Uno to power the L9110, but it was slow.
So I tried powering both the Uno and the L9110 from a 12V power brick (1A output). Power went straight from the power supply to the L19110 ground and VCC pins, and to the Uno's GND and VIN pins.
Smoke! The 5V regulator on the uno burnt out! The Uno itself isn't dead (I uploaded Blink to confirm and it's running happily off USB) but it seems I'll have to replace the 5V chip or the complete board.
What could have caused this? I used a voltmeter to confirm I didn't put more than 12V into VIN, and I thought the Uno could handle that much. Was I wrong?
Did you have anything else plugged into the Arduino like the usb cable? Maybe grounds at different potential?
Very long power supply leads can can create a problem with destructive voltage spikes just plugging them in.
What kind of regulator was it, it's not that tricky to desolder and replace.
Regulator is a little 117-5 unit, so although it's a fiddly SMD unit it's still worth the time trying to fix it.
I did have the UNO plugged in via USB, so that might have caused the issue. I had two grounds and two lives coming from the PSU, to the Uno and the motor controller, and the Uno started smoking as soon as I plugged in the VIN wire, so the motor wasn't actually drawing current at that point.
1, check the polarity on your 12V power adapter, Center pin must be +, Outer shell must be -.
2, Make sure your power wall adapter is a regulated power supply. Never use a transformer type power supply that is not regulated.
3, check the current requirements for your motor. Make sure that it does not exceed the current limits of the Arduino. Remember that the Arduino itself and all other components draws power from the Arduino. You must add them all together as well. if in doubt, use a separate power supply for the motor.
4, using a voltmeter, measure the voltage between the - of the power supply and the outer shell of the USB cable. there should be zero voltage potential. just a few millivolts should not be a problem.
Note: Unless you need 12V for something special, it is recommended that you use a 9V power supply with the Arduino. The higher input voltage means you will produce more heat through the regulator, If push too hard, this can cause it to fail.
Better to use the DC socket for 12volt.
The inline diode between DC socket and V-in drops another 0.7volt, and gives reverse voltage protection.
12volt is pushing it if the Arduino has to power something else (3.3 or 5volt).
Leo..