Hi Rob,
The link I gave you accurately measures the current from .02 amp upto 70 amps and using the ACS758 takes care of the shunt resistor as it is part of the device. The program gives you the actual current as a digital number you can use for anything you wish as well as the voltage. http://www.picbasic.co.uk/forum/showthread.php?t=16387 Best, Ed