So last night I was putting the finishing touches on a project very late into the night and I inadvertently attached a negative from my 12v battery to the positive of my control unit housing my arduino and electronics. So after the tiny spark on the v+ input and the burning smell I proceeded to bang my head on the wall (well, figuratively).
After testing the electronics directly hooked up via FTDI it appears everything does seem to work on the board so that wasn't fried. When I hooked it back up to the 12v battery however the LCD screen lights up slightly but doesn't proceed with bootup. It appears to be getting a very small voltage, which leads me to think the voltage regulator (a 7805) is shot. That sucks but I feel very lucky actually since all I need to do is replace it.
So long story short, I've learned my lesson and plan to add a protection diode before input into the regulator but I'm not quite sure what the best way to do this is. Should I put a diode prior to feeding v+ or on v-? Electron flow direction or current flow??
Any help is much appreciated!