A driver includes a sensor sensing a driving current and a driving voltage for an external device including a capacitor, a PWM, a PFC, and a controller. The pivot shaft is located forwardly of a lower idle wheel rotatably mounted to the crawler frame. After receiving the input to modify the field of view of the video sensing device, the system replaces the live feed on the display unit with alternative video data. Thereafter, contracts associated with the records are identified. An application of the invention lies in making an optical amplifier. The tubing string can be used for staged wellbore fluid treatment where a selected segment of the wellbore is treated, while other segments are sealed off.