Arduino Uno external power misbehaviour

Official Hardware UNO Family UNO R3
1

Hi there! I hope someone can help me!.

I developed a shield for the UNO to manage input and ouput signal trough optocouplers and relays for a project I´m working on. When I hooked the shield and powered externally the Arduino, the regulator blew off (I didn´t realise the shield was mistakenly connected)...

I repaired the UNO changing the voltage regulator, it works again, but I notice weird things... In the inputs pins i read between 1,5 and 1,8 Volts when the board is powered externally but when I connect the board to the USB port of my computer I read 0V.

Is this normal or there could be something else blown? the power supply I´m using is 12V. I checked the caps in the external PS section and all of them have continuity to ground. I think there´s a short somewhere...

Hope you can give me hand.

Thankyou!

2

It's impossible for anyone on the forum to diagnose what you did wrong from that description. We will need a schematic and links to the specs of all the components you used.

Taking a guess, I imagine you have several 5V relays which are powered from the 5V pin of the Uno, with the Uno powered by 12V this will totally overload the Uno's linear regulator.

It's possible that when the regulator blew, the atmega chip also got damaged.

3

PaulRB is correct. My saying which you appeared to validate is" The Arduino A Power Supply it is Not.