As a cheating and somewhat easier solution, you could always just use a 12vdc power source so as to power a charger to a 5vdc battery. then use the battery to power the meter.
I'm not sure how much of a hack that would be, but it would work. __________________ 1997 332ti - Don't even ask. 
2006 330i - ZPP/ZSP/ZCW/6sp/Nav/BT/H&R Sport
2011 E92 M3  |