A sweat collection device includes an elongate concave sweat-collecting surface at a face thereof for placement over an iontophoresis-stimulated area of a patient’s skin to collect sweat and pass it through an axial bore in the concavity. The power supply circuit also includes a PWM circuit and output driver that detects a level of an intermediate node potential at a junction point of the high side transistor and the low side transistor after turning \u201coff\u201d the high side transistor, and turning \u201con\u201d the low side transistor when the intermediate node potential becomes below or equal to a predetermined potential. The computing device obtains a data set. Both front unit and base unit magnets are of a similar circumference allowing magnetic forces to secure front unit to base unit.