An actuator includes a DC motor having two terminals to be fed with DC power, an output gear driven by the DC motor, a potentiometer having an arc resistive element with two ends and an electrically conductive wiper that moves along the resistive element, and two diodes. The wiper rotates with the output gear to provide a signal indicative of the rotational position of the output gear. The anodes of the two diodes are both electrically connected to one end of the resistive element, and the cathodes of the two diodes are electrically connected to the two terminals of the motor respectively.