An apparatus is disclosed that may include a substrate that may have a surface, a channel of a volume that may be defined, at least in part, by the substrate, wherein the channel may have a first end and a second end, a valve may be coupled to the channel at the first end, wherein the valve may be configured to allow a fluid to pass into the channel when the valve is open, and a continuity detector, which may be coupled to the channel at the second end, wherein the continuity detector may be activated when the fluid contacts the continuity detector, wherein the continuity detector may further be configured to provide a signal to close the valve and remove the fluid from the channel. A method for calculating a rate of flow of a fluid collected from a bodily surface into a body-worn device is disclosed.

A charge pumping method includes: generating a first boosted voltage by boosting an input voltage by a boosting mode of a first multiplier; changing the level of a voltage charged in at least one capacitor provided in the inside of a charge pump circuit, in preparation for a change in the boosting mode; and generating a second boosted voltage by boosting the input voltage by a boosting mode of a second multiplier.