tocpcs:
What's going on at A1 ?
A1 is a 12 volt source going through a diode and a 750 mA polyfuse for some 12 volt electronics and a motor. Negative terminals are both connected to gnd, left side positive rail has +12.2V supplied by Vin, right positive rail has +4.85V supplied by arduino 5V out.
tocpcs:
You say you are losing 2.5V through the transistor, it's connecting to ground, so are you measuring from the E pin to ground? (after the 5V has passed through the relay coil)..?
I am measuring from Collector to Emitter. I also measured across the relay coil and got about 2.3 - 2.4v
tocpcs:
I wonder if the current to initially pull the relay in is too great? And 42mA is the current to hold it in?
I hadn't thought about the pull-in current, however I measured the coil's resistance to be 121 ohms, which still works out to 5V / 121 = 0.0413 or 41.3 mA. That is just math though, and stupid reality is never as easy. :0 Do relays normally draw more current while pulling in?