A system for determining a position of a medical device within a body is provided that reduces positional error by establishing a reference origin closer to the device and/or simplifies the system by integrating components and functions. In one embodiment, a pair of drive electrodes are affixed to opposed surfaces of the body and create a pathway for transmission of current through a position sensor related to the medical device. A pair of reference electrodes proximate the drive electrodes are coupled to a common reference node outputting a reference signal establishing the reference origin. An electronic control unit determines the position of the medical device responsive to the position signal and the reference signal. In another embodiment, a patch affixed to an external surface of the body has a base layer and multiple devices supported on the base layer, electrically isolated from one another, and configured to perform different functions.