Ah I see the short... ok here's a revision...
As far as the 0.5v I guess I was confused by this comment...
@railroader "Arduino off, max 0.5 volt. A really important situation. It's a bad design if the Arduino gets killed at a power loss."
1) Is this 0.5v limitation because the previous design was monitoring the bulb by closing the circuit through the bulb... so THAT design would need to only trickle 0.5 volt... or it would harm the Arduino when the Arduino was off?
Since this circuit has 0 volts when the switch is open, I can allow 5v to the Arduino when the circuit closes? If this is the case and using your 10K suggestion... I came up with a 5.5K resistor for the other side. Based on this drawing... I'm sending the + into the Arduino.
2) Does it matter if I monitor the (+) side vs the (-)?
3) In my drawing 5.5k resistor would be R1 and the 10K would be R2 (closest to ground) does the larger value need to be R1? Does it matter?
On the 5V power supply...
4) Should Not use the barrel connector because 5v is too low?
5) Can I use the 5v pin (leaving the USB empty) so I can plug in my laptop for coding? Or do I need to feed the 5v into the USB and swap plugs when coding?