A method of fabricating a self-aligned contact is provided. In one illustrative example, a feedback circuit for a switch mode power supply is disclosed that includes two error amplifiers. An electrolyte and a mixture of one or more samples with another electrolyte are added to a microchannel or capillary. A controller receives the signals from the sensors and activates the associated roller for transport mode to assist articles through the conveyor if the path is clear, or if the downstream portion of the conveyor is blocked, to reverse the roller for accumulate mode to hold articles in the segment until the path is cleared.