I accidently left a jumper wire connected to the aref pin on my Uno and this touched a 24V DC supply on my breadboard. I get the power on LED on the Uno but nothing else. No outputs and can't connect it to my computer via USB. This is an original Uno from many years ago. Does it have a fuse or something that I've blown or is it a gonner?
AREF pin connected directly to ATmega328 microcontroller. You must have blown up that chip. If it's DIP package, change the microcontroller with new one. If SMD type, you're out of luck. Sorry for you.
DIP so maybe I'm ok. Would this account for not being able to connect via USB as well? I normally hear the telltale ding dong from windows when a device is connected and I'm not getting that. I will order a new chip anyway and see what occurs
I'm using 3 analog inputs and the values shown in serial monitor were not stable until I used aref. Don't know much about it other than it seemed to work until I removed the USB plug then the values seemed to be all over the place again (using LEDs to indicate the values). I unplugged the aref jumper from the breadboard to see if that made a difference and just left it hanging where it touched a 24V input from a voltage regulator. Stupid mistake but still not sure if the aref had anything to do with anything,
Anyway, I've ordered a new Uno (R3) and an atmega328 to try to fix the fried one so we will see what happens
Then it's better to use the internal 1.1V reference (Which is fairly stable) and use a voltage divider to bring down the signals in the measurable range.
Well, it did in the sense that Aref goes directly to the microcontroller as said by @metehoca and putting 24V on any of its pins BY FAR exceeds its maximum ratings. On the upshot your Arduino didn't suffer - she was dead in a heartbeat.
Good luck fixing it; with a little bit of luck you can get a new 328P to work on that board.