A mobile robot that includes a robot body having a forward drive direction, a drive system supporting the robot body above a cleaning surface for maneuvering the robot across the cleaning surface, and a robot controller in communication with the drive system. The robot also includes a bumper movably supported by a forward portion of the robot body and a obstacle sensor system disposed on the bumper. The obstacle sensor system includes at least one contact sensor disposed on the bumper, at least one proximity sensor disposed on the bumper and a auxiliary circuit board disposed on the bumper and in communication with the at least one contact sensor, the at least one proximity sensor, and the robot controller.