Re: Using 24VAC as an interrupt?
I didn't realize that you could bypass the regulator on an Arduino that didn't have a VCC pin! Drat. I really wanted to finish this project today, and I already wired up the circuit as I had mentioned, minus the final connection to Vin.
It sounds like if the 7805 fails it's a fairly safe device in that it shouldn't create a short or allow unregulated voltage to pass through. I think I'm going to try my luck and see what happens - hopefully the worst case being I'll pick up the buck converter and be able to power it via 5V pins.
Out of curiosity, does the amount of current consumed by the board have an effect on the energy that the 7805 must dissipate? e.g., If the board is asleep for 99% of the time, will the 7805 be running cooler because it's supplying maybe 30mA less power?